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Paolo Carlini 449c480110 lwg-active.html, [...]: Import Revision 45. 
2006-11-05  Paolo Carlini  <pcarlini@suse.de>

	* docs/html/ext/lwg-active.html, lwg-defects.html: Import Revision 45.
	* docs/html/ext/lwg-closed.html: Add.
	* docs/html/ext/howto.html: Adjust.

From-SVN: r118502
2006-11-05 16:17:03 +00:00

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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
<html><head><title>C++ Standard Library Active Issues List</title>
<style>ins {background-color:#FFFFA0}
del {background-color:#FFFFA0}</style></head>
<body bgcolor="#ffffff" text="#000000">
<table>
<tbody><tr>
<td align="left">Doc. no.</td>
<td align="left">N2130=06-0200</td>
</tr>
<tr>
<td align="left">Date:</td>
<td align="left">2006-11-03</td>
</tr>
<tr>
<td align="left">Project:</td>
<td align="left">Programming Language C++</td>
</tr>
<tr>
<td align="left">Reply to:</td>
<td align="left">Howard Hinnant &lt;howard.hinnant@gmail.com&gt;</td>
</tr>
</tbody></table>
<h1>C++ Standard Library Active Issues List (Revision R45)</h1>
<p>Reference ISO/IEC IS 14882:1998(E)</p>
<p>Also see:</p>
<ul>
<li>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-toc.html">Table of Contents</a> for all library issues.</li>
<li>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-index.html">Index by Section</a> for all library issues.</li>
<li>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-status.html">Index by Status</a> for all library issues.</li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html">Library Defect Reports List</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html">Library Closed Issues List</a></li>
</ul>
<p>The purpose of this document is to record the status of issues
which have come before the Library Working Group (LWG) of the ANSI
(J16) and ISO (WG21) C++ Standards Committee. Issues represent
potential defects in the ISO/IEC IS 14882:1998(E) document. Issues
are not to be used to request new features. </p>
<p>This document contains only library issues which are actively being
considered by the Library Working Group. That is, issues which have a
status of <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Ready">Ready</a>, and <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Review">Review</a>. See
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html">Library Defect Reports List</a> for issues considered defects and
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html">Library Closed Issues List</a> for issues considered closed.</p>
<p>The issues in these lists are not necessarily formal ISO Defect
Reports (DR's). While some issues will eventually be elevated to
official Defect Report status, other issues will be disposed of in
other ways. See <a href="#Status">Issue Status</a>.</p>
<p>This document is in an experimental format designed for both
viewing via a world-wide web browser and hard-copy printing. It
is available as an HTML file for browsing or PDF file for
printing.</p>
<p>Prior to Revision 14, library issues lists existed in two slightly
different versions; a Committee Version and a Public
Version. Beginning with Revision 14 the two versions were combined
into a single version.</p>
<p>This document includes <i>[bracketed italicized notes]</i> as a
reminder to the LWG of current progress on issues. Such notes are
strictly unofficial and should be read with caution as they may be
incomplete or incorrect. Be aware that LWG support for a particular
resolution can quickly change if new viewpoints or killer examples are
presented in subsequent discussions.</p>
<p>For the most current official version of this document see
<a href="http://www.open-std.org/jtc1/sc22/wg21/">http://www.open-std.org/jtc1/sc22/wg21/</a>.
Requests for further information about this document should include
the document number above, reference ISO/IEC 14882:1998(E), and be
submitted to Information Technology Industry Council (ITI), 1250 Eye
Street NW, Washington, DC 20005.</p>
<p>Public information as to how to obtain a copy of the C++ Standard,
join the standards committee, submit an issue, or comment on an issue
can be found in the comp.std.c++ FAQ.
Public discussion of C++ Standard related issues occurs on <a href="news://comp.std.c++/">news:comp.std.c++</a>.
</p>
<p>For committee members, files available on the committee's private
web site include the HTML version of the Standard itself. HTML
hyperlinks from this issues list to those files will only work for
committee members who have downloaded them into the same disk
directory as the issues list files. </p>
<h2>Revision History</h2>
<ul>
<li>R45:
2006-11-03 post-Portland mailing.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#520">520</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#521">521</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#530">530</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#535">535</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#537">537</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#538">538</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#540">540</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#541">541</a> to WP.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#504">504</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#512">512</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#516">516</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#544">544</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#549">549</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#554">554</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#555">555</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#558">558</a> to NAD.
Moved issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#569">569</a> to Dup.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#518">518</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#523">523</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#524">524</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#542">542</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#556">556</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#557">557</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#559">559</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#597">597</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#606">606</a> to Open.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#543">543</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#545">545</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#549">549</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#549">549</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#598">598</a> - <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#603">603</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#605">605</a> to Ready.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#531">531</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#551">551</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#604">604</a> to Review.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#593">593</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#609">609</a>.
</li>
<li>R44:
2006-09-08 pre-Portland mailing.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#583">583</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#592">592</a>.
</li>
<li>R43:
2006-06-23 mid-term mailing.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#575">575</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#582">582</a>.
Reopened <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#255">255</a>.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#520">520</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#541">541</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#544">544</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#569">569</a> to Tentatively Ready.
</li>
<li>R42:
2006-04-21 post-Berlin mailing.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#567">567</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#572">572</a>.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#499">499</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#501">501</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#506">506</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#509">509</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#511">511</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#513">513</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#514">514</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#517">517</a> to NAD.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#502">502</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#503">503</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#515">515</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#516">516</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#522">522</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#525">525</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#529">529</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#532">532</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#536">536</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#539">539</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#548">548</a> to Open.
Moved issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#504">504</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#512">512</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#521">521</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#530">530</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#531">531</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#535">535</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#537">537</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#538">538</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#540">540</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#549">549</a> to Ready.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#247">247</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#294">294</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#362">362</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#369">369</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#371">371</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#376">376</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#384">384</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#475">475</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#478">478</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#495">495</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#497">497</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#505">505</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#507">507</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#508">508</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#519">519</a> to WP.
Moved issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#534">534</a> to Review.
</li>
<li>R41:
2006-02-24 pre-Berlin mailing.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#536">536</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#566">566</a>.
Moved <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#342">342</a> from Ready to Open.
Reopened <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#309">309</a>.
</li>
<li>R40:
2005-12-16 mid-term mailing.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#529">529</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#535">535</a>.
</li>
<li>R39:
2005-10-14 post-Mont Tremblant mailing.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#526">526</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#528">528</a>.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#280">280</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#461">461</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#464">464</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#465">465</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#467">467</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#468">468</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#474">474</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#496">496</a> from Ready to WP as per the vote from Mont Tremblant.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#247">247</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#294">294</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#342">342</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#362">362</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#369">369</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#371">371</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#376">376</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#384">384</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#475">475</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#478">478</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#495">495</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#497">497</a> from Review to Ready.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#498">498</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#504">504</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#506">506</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#509">509</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#510">510</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#511">511</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#512">512</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#513">513</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#514">514</a> from New to Open.
Moved issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#505">505</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#507">507</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#508">508</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#519">519</a> from New to Ready.
Moved issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#500">500</a> from New to NAD.
Moved issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#518">518</a> from New to Review.
</li>
<li>R38:
2005-07-03 pre-Mont Tremblant mailing.
Merged open TR1 issues in <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#504">504</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#522">522</a>.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#523">523</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#523">523</a>
</li>
<li>R37:
2005-06 mid-term mailing.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#498">498</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#503">503</a>.
</li>
<li>R36:
2005-04 post-Lillehammer mailing. All issues in "ready" status except
for <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#454">454</a> were moved to "DR" status, and all issues
previously in "DR" status were moved to "WP".
</li>
<li>R35:
2005-03 pre-Lillehammer mailing.
</li>
<li>R34:
2005-01 mid-term mailing. Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#488">488</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#494">494</a>.
</li>
<li>R33:
2004-11 post-Redmond mailing. Reflects actions taken in Redmond.
</li>
<li>R32:
2004-09 pre-Redmond mailing: reflects new proposed resolutions and
new issues received after the 2004-07 mailing. Added
new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#479">479</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#481">481</a>.
</li>
<li>R31:
2004-07 mid-term mailing: reflects new proposed resolutions and
new issues received after the post-Sydney mailing. Added
new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#463">463</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#478">478</a>.
</li>
<li>R30:
Post-Sydney mailing: reflects decisions made at the Sydney meeting.
Voted all "Ready" issues from R29 into the working paper.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#460">460</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#462">462</a>.
</li>
<li>R29:
Pre-Sydney mailing. Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#441">441</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#457">457</a>.
</li>
<li>R28:
Post-Kona mailing: reflects decisions made at the Kona meeting.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#432">432</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#440">440</a>.
</li>
<li>R27:
Pre-Kona mailing. Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#404">404</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#431">431</a>.
</li>
<li>R26:
Post-Oxford mailing: reflects decisions made at the Oxford meeting.
All issues in Ready status were voted into DR status. All issues in
DR status were voted into WP status.
</li>
<li>R25:
Pre-Oxford mailing. Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#390">390</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#402">402</a>.
</li>
<li>R24:
Post-Santa Cruz mailing: reflects decisions made at the Santa Cruz
meeting. All Ready issues from R23 with the exception of <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#253">253</a>, which has been given a new proposed resolution, were
moved to DR status. Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#383">383</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#389">389</a>. (Issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#387">387</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#389">389</a> were discussed
at the meeting.) Made progress on issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#225">225</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#226">226</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#229">229</a>: <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#225">225</a> and <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#229">229</a> have been moved to Ready status, and the only remaining
concerns with <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#226">226</a> involve wording.
</li>
<li>R23:
Pre-Santa Cruz mailing. Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#367">367</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#382">382</a>.
Moved issues in the TC to TC status.
</li>
<li>R22:
Post-Cura<72>ao mailing. Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#362">362</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#366">366</a>.
</li>
<li>R21:
Pre-Cura<72>ao mailing. Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#351">351</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#361">361</a>.
</li>
<li>R20:
Post-Redmond mailing; reflects actions taken in Redmond. Added
new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#336">336</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#350">350</a>, of which issues
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#347">347</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#350">350</a> were added since Redmond, hence
not discussed at the meeting.
All Ready issues were moved to DR status, with the exception of issues
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#284">284</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#241">241</a>, and <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#267">267</a>.
Noteworthy issues discussed at Redmond include
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#120">120</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#202">202</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#226">226</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#233">233</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#270">270</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#253">253</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#254">254</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#323">323</a>.
</li>
<li>R19:
Pre-Redmond mailing. Added new issues
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#323">323</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#335">335</a>.
</li>
<li>R18:
Post-Copenhagen mailing; reflects actions taken in Copenhagen.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#312">312</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#317">317</a>, and discussed
new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#271">271</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#314">314</a>.
Changed status of issues
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#103">103</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#118">118</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#136">136</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#153">153</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#165">165</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#171">171</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#183">183</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#184">184</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#185">185</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#186">186</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#214">214</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#221">221</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#234">234</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#237">237</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#243">243</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#248">248</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#251">251</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#252">252</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#256">256</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#260">260</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#261">261</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#262">262</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#263">263</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#265">265</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#268">268</a>
to DR.
Changed status of issues
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#49">49</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#109">109</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#117">117</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#182">182</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#228">228</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#230">230</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#232">232</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#235">235</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#238">238</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#241">241</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#242">242</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#250">250</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#259">259</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#264">264</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#266">266</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#267">267</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#271">271</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#272">272</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#273">273</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#275">275</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#281">281</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#284">284</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#285">285</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#286">286</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#288">288</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#292">292</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#295">295</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#297">297</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#298">298</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#301">301</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#303">303</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#306">306</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#307">307</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#308">308</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#312">312</a>
to Ready.
Closed issues
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#111">111</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#277">277</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#279">279</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#287">287</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#289">289</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#293">293</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#302">302</a> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#313">313</a>
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#314">314</a>
as NAD.
</li>
<li>R17:
Pre-Copenhagen mailing. Converted issues list to XML. Added proposed
resolutions for issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#49">49</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#76">76</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#91">91</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#235">235</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#250">250</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#267">267</a>.
Added new issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#278">278</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#311">311</a>.
</li>
<li>R16:
post-Toronto mailing; reflects actions taken in Toronto. Added new
issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#265">265</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#277">277</a>. Changed status of issues
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#3">3</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#8">8</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#9">9</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#19">19</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#26">26</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#31">31</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#61">61</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#63">63</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#86">86</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#108">108</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#112">112</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#114">114</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#115">115</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#122">122</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#127">127</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#129">129</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#134">134</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#137">137</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#142">142</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#144">144</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#146">146</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#147">147</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#159">159</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#164">164</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#170">170</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#181">181</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#199">199</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#208">208</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#209">209</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#210">210</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#211">211</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#212">212</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#217">217</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#220">220</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#222">222</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#223">223</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#224">224</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#227">227</a> to "DR". Reopened issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#23">23</a>. Reopened
issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#187">187</a>. Changed issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#2">2</a> and
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#4">4</a> to NAD. Fixed a typo in issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#17">17</a>. Fixed
issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#70">70</a>: signature should be changed both places it
appears. Fixed issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#160">160</a>: previous version didn't fix
the bug in enough places.
</li>
<li>R15:
pre-Toronto mailing. Added issues
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#233">233</a>-<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#264">264</a>. Some small HTML formatting
changes so that we pass Weblint tests.
</li>
<li>R14:
post-Tokyo II mailing; reflects committee actions taken in
Tokyo. Added issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#228">228</a> to <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#232">232</a>. (00-0019R1/N1242)
</li>
<li>R13:
pre-Tokyo II updated: Added issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#212">212</a> to <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#227">227</a>.
</li>
<li>R12:
pre-Tokyo II mailing: Added issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#199">199</a> to
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#211">211</a>. Added "and paragraph 5" to the proposed resolution
of issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#29">29</a>. Add further rationale to issue
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#178">178</a>.
</li>
<li>R11:
post-Kona mailing: Updated to reflect LWG and full committee actions
in Kona (99-0048/N1224). Note changed resolution of issues
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#4">4</a> and <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#38">38</a>. Added issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#196">196</a>
to <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#198">198</a>. Closed issues list split into "defects" and
"closed" documents. Changed the proposed resolution of issue
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#4">4</a> to NAD, and changed the wording of proposed resolution
of issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#38">38</a>.
</li>
<li>R10:
pre-Kona updated. Added proposed resolutions <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#83">83</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#86">86</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#91">91</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#92">92</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#109">109</a>. Added issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#190">190</a> to
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#195">195</a>. (99-0033/D1209, 14 Oct 99)
</li>
<li>R9:
pre-Kona mailing. Added issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#140">140</a> to
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#189">189</a>. Issues list split into separate "active" and
"closed" documents. (99-0030/N1206, 25 Aug 99)
</li>
<li>R8:
post-Dublin mailing. Updated to reflect LWG and full committee actions
in Dublin. (99-0016/N1193, 21 Apr 99)
</li>
<li>R7:
pre-Dublin updated: Added issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#130">130</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#131">131</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#132">132</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#133">133</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#134">134</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#135">135</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#136">136</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#137">137</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#138">138</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#139">139</a> (31 Mar 99)
</li>
<li>R6:
pre-Dublin mailing. Added issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#127">127</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#128">128</a>,
and <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#129">129</a>. (99-0007/N1194, 22 Feb 99)
</li>
<li>R5:
update issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#103">103</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#112">112</a>; added issues
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#114">114</a> to <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#126">126</a>. Format revisions to prepare
for making list public. (30 Dec 98)
</li>
<li>R4:
post-Santa Cruz II updated: Issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#110">110</a>,
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#111">111</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#112">112</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#113">113</a> added, several
issues corrected. (22 Oct 98)
</li>
<li>R3:
post-Santa Cruz II: Issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#94">94</a> to <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#109">109</a>
added, many issues updated to reflect LWG consensus (12 Oct 98)
</li>
<li>R2:
pre-Santa Cruz II: Issues <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#73">73</a> to <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#93">93</a> added,
issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#17">17</a> updated. (29 Sep 98)
</li>
<li>R1:
Correction to issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#55">55</a> resolution, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#60">60</a> code
format, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#64">64</a> title. (17 Sep 98)
</li>
</ul>
<h2>
<a name="Status"></a>Issue Status</h2>
<p><b><a name="New">New</a></b> - The issue has not yet been
reviewed by the LWG. Any <b>Proposed Resolution</b> is purely a
suggestion from the issue submitter, and should not be construed as
the view of LWG.</p>
<p><b><a name="Open">Open</a></b> - The LWG has discussed the issue
but is not yet ready to move the issue forward. There are several
possible reasons for open status:</p>
<ul>
<li>Consensus may have not yet have been reached as to how to deal
with the issue.</li>
<li>Informal consensus may have been reached, but the LWG awaits
exact <b>Proposed Resolution</b> wording for review.</li>
<li>The LWG wishes to consult additional technical experts before
proceeding.</li>
<li>The issue may require further study.</li>
</ul>
<p>A <b>Proposed Resolution</b> for an open issue is still not be
construed as the view of LWG. Comments on the current state of
discussions are often given at the end of open issues in an italic
font. Such comments are for information only and should not be given
undue importance.</p>
<p><b><a name="Dup">Dup</a></b> - The LWG has reached consensus that
the issue is a duplicate of another issue, and will not be further
dealt with. A <b>Rationale</b> identifies the duplicated issue's
issue number. </p>
<p><b><a name="NAD">NAD</a></b> - The LWG has reached consensus that
the issue is not a defect in the Standard, and the issue is ready to
forward to the full committee as a proposed record of response. A
<b>Rationale</b> discusses the LWG's reasoning.</p>
<p><b><a name="Review">Review</a></b> - Exact wording of a
<b>Proposed Resolution</b> is now available for review on an issue
for which the LWG previously reached informal consensus.</p>
<p><b><a name="Tentatively Ready">Tentatively Ready</a></b> - The issue has
been reviewed online, but not in a meeting, and some support has been formed
for the proposed resolution. Tentatively Ready issues may be moved to Ready
and forwarded to full committee within the same meeting. Unlike Ready issues
they will be reviewed in subcommittee prior to forwarding to full committee.</p>
<p><b><a name="Ready">Ready</a></b> - The LWG has reached consensus
that the issue is a defect in the Standard, the <b>Proposed
Resolution</b> is correct, and the issue is ready to forward to the
full committee for further action as a Defect Report (DR).</p>
<p><b><a name="DR">DR</a></b> - (Defect Report) - The full J16
committee has voted to forward the issue to the Project Editor to be
processed as a Potential Defect Report. The Project Editor reviews
the issue, and then forwards it to the WG21 Convenor, who returns it
to the full committee for final disposition. This issues list
accords the status of DR to all these Defect Reports regardless of
where they are in that process.</p>
<p><b><a name="TC">TC</a></b> - (Technical Corrigenda) - The full
WG21 committee has voted to accept the Defect Report's Proposed
Resolution as a Technical Corrigenda. Action on this issue is thus
complete and no further action is possible under ISO rules.</p>
<p><b><a name="WP">WP</a></b> - (Working Paper) - The proposed
resolution has not been accepted as a Technical Corrigendum, but
the full WG21 committee has voted to apply the Defect Report's Proposed
Resolution to the working paper.</p>
<p><b><a name="RR">RR</a></b> - (Record of Response) - The full WG21
committee has determined that this issue is not a defect in the
Standard. Action on this issue is thus complete and no further
action is possible under ISO rules.</p>
<p><b><a name="Future">Future</a></b> - In addition to the regular
status, the LWG believes that this issue should be revisited at the
next revision of the standard. It is usually paired with NAD.</p>
<p>Issues are always given the status of <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a> when
they first appear on the issues list. They may progress to
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a> or <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Review">Review</a> while the LWG
is actively working on them. When the LWG has reached consensus on
the disposition of an issue, the status will then change to
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Dup">Dup</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#NAD">NAD</a>, or <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Ready">Ready</a> as appropriate. Once the full J16 committee votes to
forward Ready issues to the Project Editor, they are given the
status of Defect Report ( <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#DR">DR</a>). These in turn may
become the basis for Technical Corrigenda (<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#TC">TC</a>),
or are closed without action other than a Record of Response
(<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#RR">RR</a> ). The intent of this LWG process is that
only issues which are truly defects in the Standard move to the
formal ISO DR status.
</p>
<h2>Active Issues</h2>
<hr>
<a name="23"><h3>23.&nbsp;Num_get overflow result</h3></a><p><b>Section:</b>&nbsp;22.2.2.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-locales.html#lib.facet.num.get.virtuals"> [lib.facet.num.get.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Nathan Myers&nbsp; <b>Date:</b>&nbsp;6 Aug 1998</p>
<p>The current description of numeric input does not account for the
possibility of overflow. This is an implicit result of changing the
description to rely on the definition of scanf() (which fails to
report overflow), and conflicts with the documented behavior of
traditional and current implementations. </p>
<p>Users expect, when reading a character sequence that results in a
value unrepresentable in the specified type, to have an error
reported. The standard as written does not permit this. </p>
<p><b>Further comments from Dietmar:</b></p>
<p>
I don't feel comfortable with the proposed resolution to issue 23: It
kind of simplifies the issue to much. Here is what is going on:
</p>
<p>
Currently, the behavior of numeric overflow is rather counter intuitive
and hard to trace, so I will describe it briefly:
</p>
<ul>
<li>
According to 22.2.2.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-locales.html#lib.facet.num.get.virtuals"> [lib.facet.num.get.virtuals]</a>
paragraph 11 <tt>failbit</tt> is set if <tt>scanf()</tt> would
return an input error; otherwise a value is converted to the rules
of <tt>scanf</tt>.
</li>
<li>
<tt>scanf()</tt> is defined in terms of <tt>fscanf()</tt>.
</li>
<li>
<tt>fscanf()</tt> returns an input failure if during conversion no
character matching the conversion specification could be extracted
before reaching EOF. This is the only reason for <tt>fscanf()</tt>
to fail due to an input error and clearly does not apply to the case
of overflow.
</li>
<li>
Thus, the conversion is performed according to the rules of
<tt>fscanf()</tt> which basically says that <tt>strtod</tt>,
<tt>strtol()</tt>, etc. are to be used for the conversion.
</li>
<li>
The <tt>strtod()</tt>, <tt>strtol()</tt>, etc. functions consume as
many matching characters as there are and on overflow continue to
consume matching characters but also return a value identical to
the maximum (or minimum for signed types if there was a leading minus)
value of the corresponding type and set <tt>errno</tt> to <tt>ERANGE</tt>.
</li>
<li>
Thus, according to the current wording in the standard, overflows
can be detected! All what is to be done is to check <tt>errno</tt>
after reading an element and, of course, clearing <tt>errno</tt>
before trying a conversion. With the current wording, it can be
detected whether the overflow was due to a positive or negative
number for signed types.
</li>
</ul>
<p><b>Further discussion from Redmond:</b></p>
<p>The basic problem is that we've defined our behavior,
including our error-reporting behavior, in terms of C90. However,
C90's method of reporting overflow in scanf is not technically an
"input error". The <tt>strto_*</tt> functions are more precise.</p>
<p>There was general consensus that <tt>failbit</tt> should be set
upon overflow. We considered three options based on this:</p>
<ol>
<li>Set failbit upon conversion error (including overflow), and
don't store any value.</li>
<li>Set failbit upon conversion error, and also set <tt>errno</tt> to
indicated the precise nature of the error.</li>
<li>Set failbit upon conversion error. If the error was due to
overflow, store +-numeric_limits&lt;T&gt;::max() as an
overflow indication.</li>
</ol>
<p>Straw poll: (1) 5; (2) 0; (3) 8.</p>
<p><b>Proposed resolution:</b></p>
<p>Discussed at Lillehammer. General outline of what we want the
solution to look like: we want to say that overflow is an error, and
provide a way to distinguish overflow from other kinds of errors.
Choose candidate field the same way scanf does, but don't describe
the rest of the process in terms of format. If a finite input field
is too large (positive or negative) to be represented as a finite
value, then set failbit and assign the nearest representable value.
Bill will provide wording.</p>
<hr>
<a name="96"><h3>96.&nbsp;Vector&lt;bool&gt; is not a container</h3></a><p><b>Section:</b>&nbsp;23.2.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.vector"> [lib.vector]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;AFNOR&nbsp; <b>Date:</b>&nbsp;7 Oct 1998</p>
<p><tt>vector&lt;bool&gt;</tt> is not a container as its reference and
pointer types are not references and pointers. </p>
<p>Also it forces everyone to have a space optimization instead of a
speed one.</p>
<p><b>See also:</b> 99-0008 == N1185 Vector&lt;bool&gt; is
Nonconforming, Forces Optimization Choice.</p>
<p><b>Proposed resolution:</b></p>
<p><i>[In Santa Cruz the LWG felt that this was Not A Defect.]</i></p>
<p><i>[In Dublin many present felt that failure to meet Container
requirements was a defect. There was disagreement as to whether
or not the optimization requirements constituted a defect.]</i></p>
<p><i>[The LWG looked at the following resolutions in some detail:
<br>
&nbsp;&nbsp;&nbsp;&nbsp; * Not A Defect.<br>
&nbsp;&nbsp;&nbsp;&nbsp; * Add a note explaining that vector&lt;bool&gt; does not meet
Container requirements.<br>
&nbsp;&nbsp;&nbsp;&nbsp; * Remove vector&lt;bool&gt;.<br>
&nbsp;&nbsp;&nbsp;&nbsp; * Add a new category of container requirements which
vector&lt;bool&gt; would meet.<br>
&nbsp;&nbsp;&nbsp;&nbsp; * Rename vector&lt;bool&gt;.<br>
<br>
No alternative had strong, wide-spread, support and every alternative
had at least one "over my dead body" response.<br>
<br>
There was also mention of a transition scheme something like (1) add
vector_bool and deprecate vector&lt;bool&gt; in the next standard. (2)
Remove vector&lt;bool&gt; in the following standard.]</i></p>
<p><i>[Modifying container requirements to permit returning proxies
(thus allowing container requirements conforming vector&lt;bool&gt;)
was also discussed.]</i></p>
<p><i>[It was also noted that there is a partial but ugly workaround in
that vector&lt;bool&gt; may be further specialized with a customer
allocator.]</i></p>
<p><i>[Kona: Herb Sutter presented his paper J16/99-0035==WG21/N1211,
vector&lt;bool&gt;: More Problems, Better Solutions. Much discussion
of a two step approach: a) deprecate, b) provide replacement under a
new name. LWG straw vote on that: 1-favor, 11-could live with, 2-over
my dead body. This resolution was mentioned in the LWG report to the
full committee, where several additional committee members indicated
over-my-dead-body positions.]</i></p>
<p>Discussed at Lillehammer. General agreement that we should
deprecate vector&lt;bool&gt; and introduce this functionality under
a different name, e.g. bit_vector. This might make it possible to
remove the vector&lt;bool&gt; specialization in the standard that comes
after C++0x. There was also a suggestion that
in C++0x we could additional say that it's implementation defined
whether vector&lt;bool&gt; refers to the specialization or to the
primary template, but there wasn't general agreement that this was a
good idea.</p>
<p>We need a paper for the new bit_vector class.</p>
<hr>
<a name="201"><h3>201.&nbsp;Numeric limits terminology wrong</h3></a><p><b>Section:</b>&nbsp;18.2.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-support.html#lib.limits"> [lib.limits]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Stephen Cleary&nbsp; <b>Date:</b>&nbsp;21 Dec 1999</p>
<p>
In some places in this section, the terms "fundamental types" and
"scalar types" are used when the term "arithmetic types" is intended.
The current usage is incorrect because void is a fundamental type and
pointers are scalar types, neither of which should have
specializations of numeric_limits.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Lillehammer: it remains true that numeric_limits is using
imprecise language. However, none of the proposals for changed
wording are clearer. A redesign of numeric_limits is needed, but this
is more a task than an open issue.]</i></p>
<hr>
<a name="206"><h3>206.&nbsp;operator new(size_t, nothrow) may become unlinked to ordinary operator new if ordinary version replaced</h3></a><p><b>Section:</b>&nbsp;18.5.1.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-support.html#lib.new.delete.single"> [lib.new.delete.single]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Howard Hinnant&nbsp; <b>Date:</b>&nbsp;29 Aug 1999</p>
<p>As specified, the implementation of the nothrow version of operator
new does not necessarily call the ordinary operator new, but may
instead simply call the same underlying allocator and return a null
pointer instead of throwing an exception in case of failure.</p>
<p>Such an implementation breaks code that replaces the ordinary
version of new, but not the nothrow version. If the ordinary version
of new/delete is replaced, and if the replaced delete is not
compatible with pointers returned from the library versions of new,
then when the replaced delete receives a pointer allocated by the
library new(nothrow), crash follows.</p>
<p>The fix appears to be that the lib version of new(nothrow) must
call the ordinary new. Thus when the ordinary new gets replaced, the
lib version will call the replaced ordinary new and things will
continue to work.</p>
<p>An alternative would be to have the ordinary new call
new(nothrow). This seems sub-optimal to me as the ordinary version of
new is the version most commonly replaced in practice. So one would
still need to replace both ordinary and nothrow versions if one wanted
to replace the ordinary version.</p>
<p>Another alternative is to put in clear text that if one version is
replaced, then the other must also be replaced to maintain
compatibility. Then the proposed resolution below would just be a
quality of implementation issue. There is already such text in
paragraph 7 (under the new(nothrow) version). But this nuance is
easily missed if one reads only the paragraphs relating to the
ordinary new.</p>
<p><b>Proposed resolution:</b></p>
<p><b>Rationale:</b></p>
<p>Yes, they may become unlinked, and that is by design. If a user
replaces one, the user should also replace the other.</p>
<p><i>[
Reopened due to a gcc conversation between Howard, Martin and Gaby. Forwarding
or not is visible behavior to the client and it would be useful for the client
to know which behavior it could depend on.
]</i></p>
<hr>
<a name="233"><h3>233.&nbsp;Insertion hints in associative containers</h3></a><p><b>Section:</b>&nbsp;23.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.associative.reqmts"> [lib.associative.reqmts]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Andrew Koenig&nbsp; <b>Date:</b>&nbsp;30 Apr 2000</p>
<p>
If <tt>mm</tt> is a multimap and <tt>p</tt> is an iterator
into the multimap, then <tt>mm.insert(p, x)</tt> inserts
<tt>x</tt> into <tt>mm</tt> with <tt>p</tt> as a hint as
to where it should go. Table 69 claims that the execution time is
amortized constant if the insert winds up taking place adjacent to
<tt>p</tt>, but does not say when, if ever, this is guaranteed to
happen. All it says it that <tt>p</tt> is a hint as to where to
insert.
</p>
<p>
The question is whether there is any guarantee about the relationship
between <tt>p</tt> and the insertion point, and, if so, what it
is.
</p>
<p>
I believe the present state is that there is no guarantee: The user
can supply <tt>p</tt>, and the implementation is allowed to
disregard it entirely.
</p>
<p><b>Additional comments from Nathan:</b><br>
The vote [in Redmond] was on whether to elaborately specify the use of
the hint, or to require behavior only if the value could be inserted
adjacent to the hint. I would like to ensure that we have a chance to
vote for a deterministic treatment: "before, if possible, otherwise
after, otherwise anywhere appropriate", as an alternative to the
proposed "before or after, if possible, otherwise [...]".
</p>
<p><b>Proposed resolution:</b></p>
<p>In table 69 "Associative Container Requirements" in 23.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.associative.reqmts"> [lib.associative.reqmts]</a>, in the row for <tt>a.insert(p, t)</tt>,
change</p>
<blockquote>
iterator p is a hint pointing to where the insert
should start to search.
</blockquote>
<p>to</p>
<blockquote>
insertion adjacent to iterator p is preferred if
more than one insertion point is valid.
</blockquote>
<p>and change</p>
<blockquote>
logarithmic in general, but amortized constant if
t is inserted right after p.
</blockquote>
<p>to</p>
<blockquote>
logarithmic in general, but amortized constant if
t is inserted adjacent to iterator p.
</blockquote>
<p><i>[Toronto: there was general agreement that this is a real defect:
when inserting an element x into a multiset that already contains
several copies of x, there is no way to know whether the hint will be
used. The proposed resolution was that the new element should always
be inserted as close to the hint as possible. So, for example, if
there is a subsequence of equivalent values, then providing a.begin()
as the hint means that the new element should be inserted before the
subsequence even if a.begin() is far away. JC van Winkel supplied
precise wording for this proposed resolution, and also for an
alternative resolution in which hints are only used when they are
adjacent to the insertion point.]</i></p>
<p><i>[Copenhagen: the LWG agreed to the original proposed resolution,
in which an insertion hint would be used even when it is far from the
insertion point. This was contingent on seeing a reference
implementation showing that it is possible to implement this
requirement without loss of efficiency. John Potter provided such a
reference implementation.]</i></p>
<p><i>[Redmond: The LWG was reluctant to adopt the proposal that
emerged from Copenhagen: it seemed excessively complicated, and went
beyond fixing the defect that we identified in Toronto. PJP provided
the new wording described in this issue. Nathan agrees that we
shouldn't adopt the more detailed semantics, and notes: "we know that
you can do it efficiently enough with a red-black tree, but there are
other (perhaps better) balanced tree techniques that might differ
enough to make the detailed semantics hard to satisfy."]</i></p>
<p><i>[Cura<72>ao: Nathan should give us the alternative wording he
suggests so the LWG can decide between the two options.]</i></p>
<p><i>[Lillehammer: The LWG previously rejected the more detailed
semantics, because it seemed more loike a new feature than like
defect fixing. We're now more sympathetic to it, but we (especially
Bill) are still worried about performance. N1780 describes a naive
algorithm, but it's not clear whether there is a non-naive
implementation. Is it possible to implement this as efficently as
the current version of insert?]</i></p>
<p><i>[Post Lillehammer: N1780 updated in post meeting mailing with
feedback from Lillehammer with more information regarding performance.
]</i></p>
<hr>
<a name="254"><h3>254.&nbsp;Exception types in clause 19 are constructed from <tt>std::string</tt>
</h3></a><p><b>Section:</b>&nbsp;19.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-diagnostics.html#lib.std.exceptions"> [lib.std.exceptions]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Dave Abrahams&nbsp; <b>Date:</b>&nbsp;01 Aug 2000</p>
<p>
Many of the standard exception types which implementations are
required to throw are constructed with a const std::string&amp;
parameter. For example:
</p>
<pre> 19.1.5 Class out_of_range [lib.out.of.range]
namespace std {
class out_of_range : public logic_error {
public:
explicit out_of_range(const string&amp; what_arg);
};
}
1 The class out_of_range defines the type of objects thrown as excep-
tions to report an argument value not in its expected range.
out_of_range(const string&amp; what_arg);
Effects:
Constructs an object of class out_of_range.
Postcondition:
strcmp(what(), what_arg.c_str()) == 0.
</pre>
<p>
There are at least two problems with this:
</p>
<ol>
<li>A program which is low on memory may end up throwing
std::bad_alloc instead of out_of_range because memory runs out while
constructing the exception object.</li>
<li>An obvious implementation which stores a std::string data member
may end up invoking terminate() during exception unwinding because the
exception object allocates memory (or rather fails to) as it is being
copied.</li>
</ol>
<p>
There may be no cure for (1) other than changing the interface to
out_of_range, though one could reasonably argue that (1) is not a
defect. Personally I don't care that much if out-of-memory is reported
when I only have 20 bytes left, in the case when out_of_range would
have been reported. People who use exception-specifications might care
a lot, though.
</p>
<p>
There is a cure for (2), but it isn't completely obvious. I think a
note for implementors should be made in the standard. Avoiding
possible termination in this case shouldn't be left up to chance. The
cure is to use a reference-counted "string" implementation
in the exception object. I am not necessarily referring to a
std::string here; any simple reference-counting scheme for a NTBS
would do.
</p>
<p><b>Further discussion, in email:</b></p>
<p>
...I'm not so concerned about (1). After all, a library implementation
can add const char* constructors as an extension, and users don't
<i>need</i> to avail themselves of the standard exceptions, though this is
a lame position to be forced into. FWIW, std::exception and
std::bad_alloc don't require a temporary basic_string.
</p>
<p>
...I don't think the fixed-size buffer is a solution to the problem,
strictly speaking, because you can't satisfy the postcondition
<br>
<tt>&nbsp;&nbsp;strcmp(what(), what_arg.c_str()) == 0</tt>
<br>
For all values of what_arg (i.e. very long values). That means that
the only truly conforming solution requires a dynamic allocation.
</p>
<p><b>Further discussion, from Redmond:</b></p>
<p>The most important progress we made at the Redmond meeting was
realizing that there are two separable issues here: the const
string&amp; constructor, and the copy constructor. If a user writes
something like <tt>throw std::out_of_range("foo")</tt>, the const
string&amp; constructor is invoked before anything gets thrown. The
copy constructor is potentially invoked during stack unwinding.</p>
<p>The copy constructor is a more serious problem, becuase failure
during stack unwinding invokes <tt>terminate</tt>. The copy
constructor must be nothrow. <i>Cura<EFBFBD>ao: Howard thinks this
requirement may already be present.</i></p>
<p>The fundamental problem is that it's difficult to get the nothrow
requirement to work well with the requirement that the exception
objects store a string of unbounded size, particularly if you also try
to make the const string&amp; constructor nothrow. Options discussed
include:</p>
<ul>
<li>Limit the size of a string that exception objects are required to
throw: change the postconditions of 19.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-diagnostics.html#lib.domain.error"> [lib.domain.error]</a> paragraph 3
and 19.1.6 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-diagnostics.html#lib.runtime.error"> [lib.runtime.error]</a> paragraph 3 to something like this:
"strncmp(what(), what_arg._str(), N) == 0, where N is an
implementation defined constant no smaller than 256".</li>
<li>Allow the const string&amp; constructor to throw, but not the
copy constructor. It's the implementor's responsibility to get it
right. (An implementor might use a simple refcount class.)</li>
<li>Compromise between the two: an implementation is not allowed to
throw if the string's length is less than some N, but, if it doesn't
throw, the string must compare equal to the argument.</li>
<li>Add a new constructor that takes a const char*</li>
</ul>
<p>(Not all of these options are mutually exclusive.)</p>
<p><b>Proposed resolution:</b></p>
<p><b>Rationale:</b></p>
<p>Throwing a bad_alloc while trying to construct a message for another
exception-derived class is not necessarily a bad thing. And the
bad_alloc constructor already has a no throw spec on it (18.4.2.1).</p>
<p><b>Future:</b></p>
<p>All involved would like to see const char* constructors added, but
this should probably be done for C++0X as opposed to a DR.</p>
<p>I believe the no throw specs currently decorating these functions
could be improved by some kind of static no throw spec checking
mechanism (in a future C++ language). As they stand, the copy
constructors might fail via a call to unexpected. I think what is
intended here is that the copy constructors can't fail.</p>
<p><i>[Pre-Sydney: reopened at the request of Howard Hinnant.
Post-Redmond: James Kanze noticed that the copy constructors of
exception-derived classes do not have nothrow clauses. Those
classes have no copy constructors declared, meaning the
compiler-generated implicit copy constructors are used, and those
compiler-generated constructors might in principle throw anything.]</i></p>
<hr>
<a name="255"><h3>255.&nbsp;Why do <tt>basic_streambuf&lt;&gt;::pbump()</tt> and <tt>gbump()</tt> take an int?</h3></a><p><b>Section:</b>&nbsp;27.5.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.streambuf"> [lib.streambuf]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;12 Aug 2000</p>
<p>
The basic_streambuf members gbump() and pbump() are specified to take an
int argument. This requirement prevents the functions from effectively
manipulating buffers larger than std::numeric_limits&lt;int&gt;::max()
characters. It also makes the common use case for these functions
somewhat difficult as many compilers will issue a warning when an
argument of type larger than int (such as ptrdiff_t on LLP64
architectures) is passed to either of the function. Since it's often the
result of the subtraction of two pointers that is passed to the
functions, a cast is necessary to silence such warnings. Finally, the
usage of a native type in the functions signatures is inconsistent with
other member functions (such as sgetn() and sputn()) that manipulate the
underlying character buffer. Those functions take a streamsize argument.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change the signatures of these functions in the synopsis of template
class basic_streambuf (27.5.2) and in their descriptions (27.5.2.3.1, p4
and 27.5.2.3.2, p4) to take a streamsize argument.
</p>
<p>
Although this change has the potential of changing the ABI of the
library, the change will affect only platforms where int is different
than the definition of streamsize. However, since both functions are
typically inline (they are on all known implementations), even on such
platforms the change will not affect any user code unless it explicitly
relies on the existing type of the functions (e.g., by taking their
address). Such a possibility is IMO quite remote.
</p>
<p>
Alternate Suggestion from Howard Hinnant, c++std-lib-7780:
</p>
<p>
This is something of a nit, but I'm wondering if streamoff wouldn't be a
better choice than streamsize. The argument to pbump and gbump MUST be
signed. But the standard has this to say about streamsize
(27.4.1/2/Footnote):
</p>
<blockquote>
[Footnote: streamsize is used in most places where ISO C would use
size_t. Most of the uses of streamsize could use size_t, except for
the strstreambuf constructors, which require negative values. It
should probably be the signed type corresponding to size_t (which is
what Posix.2 calls ssize_t). --- end footnote]
</blockquote>
<p>
This seems a little weak for the argument to pbump and gbump. Should we
ever really get rid of strstream, this footnote might go with it, along
with the reason to make streamsize signed.
</p>
<p><b>Rationale:</b></p>
<p>The LWG believes this change is too big for now. We may wish to
reconsider this for a future revision of the standard. One
possibility is overloading pbump, rather than changing the
signature.</p>
<p><i>[
[2006-05-04: Reopened at the request of Chris (Krzysztof ?elechowski)]
]</i></p>
<hr>
<a name="258"><h3>258.&nbsp;Missing allocator requirement</h3></a><p><b>Section:</b>&nbsp;20.1.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.default.con.req"> [lib.default.con.req]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;22 Aug 2000</p>
<p>
From lib-7752:
</p>
<p>
I've been assuming (and probably everyone else has been assuming) that
allocator instances have a particular property, and I don't think that
property can be deduced from anything in Table 32.
</p>
<p>
I think we have to assume that allocator type conversion is a
homomorphism. That is, if x1 and x2 are of type X, where
X::value_type is T, and if type Y is X::template
rebind&lt;U&gt;::other, then Y(x1) == Y(x2) if and only if x1 == x2.
</p>
<p>
Further discussion: Howard Hinnant writes, in lib-7757:
</p>
<p>
I think I can prove that this is not provable by Table 32. And I agree
it needs to be true except for the "and only if". If x1 != x2, I see no
reason why it can't be true that Y(x1) == Y(x2). Admittedly I can't
think of a practical instance where this would happen, or be valuable.
But I also don't see a need to add that extra restriction. I think we
only need:
</p>
<blockquote>
if (x1 == x2) then Y(x1) == Y(x2)
</blockquote>
<p>
If we decide that == on allocators is transitive, then I think I can
prove the above. But I don't think == is necessarily transitive on
allocators. That is:
</p>
<p>
Given x1 == x2 and x2 == x3, this does not mean x1 == x3.
</p>
<p>Example:</p>
<blockquote>
<p>
x1 can deallocate pointers from: x1, x2, x3 <br>
x2 can deallocate pointers from: x1, x2, x4 <br>
x3 can deallocate pointers from: x1, x3 <br>
x4 can deallocate pointers from: x2, x4
</p>
<p>
x1 == x2, and x2 == x4, but x1 != x4
</p>
</blockquote>
<p><b>Proposed resolution:</b></p>
<p><i>[Toronto: LWG members offered multiple opinions. One
opinion is that it should not be required that <tt>x1 == x2</tt>
implies <tt>Y(x1) == Y(x2)</tt>, and that it should not even be
required that <tt>X(x1) == x1</tt>. Another opinion is that
the second line from the bottom in table 32 already implies the
desired property. This issue should be considered in light of
other issues related to allocator instances.]</i></p>
<hr>
<a name="290"><h3>290.&nbsp;Requirements to for_each and its function object</h3></a><p><b>Section:</b>&nbsp;25.1.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-algorithms.html#lib.alg.foreach"> [lib.alg.foreach]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Angelika Langer&nbsp; <b>Date:</b>&nbsp;03 Jan 2001</p>
<p>The specification of the for_each algorithm does not have a
"Requires" section, which means that there are no
restrictions imposed on the function object whatsoever. In essence it
means that I can provide any function object with arbitrary side
effects and I can still expect a predictable result. In particular I
can expect that the function object is applied exactly last - first
times, which is promised in the "Complexity" section.
</p>
<p>I don't see how any implementation can give such a guarantee
without imposing requirements on the function object.
</p>
<p>Just as an example: consider a function object that removes
elements from the input sequence. In that case, what does the
complexity guarantee (applies f exactly last - first times) mean?
</p>
<p>One can argue that this is obviously a nonsensical application and
a theoretical case, which unfortunately it isn't. I have seen
programmers shooting themselves in the foot this way, and they did not
understand that there are restrictions even if the description of the
algorithm does not say so.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Lillehammer: This is more general than for_each. We don't want
the function object in transform invalidiating iterators
either. There should be a note somewhere in clause 17 (17, not 25)
saying that user code operating on a range may not invalidate
iterators unless otherwise specified. Bill will provide wording.]</i></p>
<hr>
<a name="299"><h3>299.&nbsp;Incorrect return types for iterator dereference</h3></a><p><b>Section:</b>&nbsp;24.1.4 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iterators.html#lib.bidirectional.iterators"> [lib.bidirectional.iterators]</a>, 24.1.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iterators.html#lib.random.access.iterators"> [lib.random.access.iterators]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;John Potter&nbsp; <b>Date:</b>&nbsp;22 Jan 2001</p>
<p>
In section 24.1.4 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iterators.html#lib.bidirectional.iterators"> [lib.bidirectional.iterators]</a>,
Table 75 gives the return type of *r-- as convertible to T. This is
not consistent with Table 74 which gives the return type of *r++ as
T&amp;. *r++ = t is valid while *r-- = t is invalid.
</p>
<p>
In section 24.1.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iterators.html#lib.random.access.iterators"> [lib.random.access.iterators]</a>,
Table 76 gives the return type of a[n] as convertible to T. This is
not consistent with the semantics of *(a + n) which returns T&amp; by
Table 74. *(a + n) = t is valid while a[n] = t is invalid.
</p>
<p>
Discussion from the Copenhagen meeting: the first part is
uncontroversial. The second part, operator[] for Random Access
Iterators, requires more thought. There are reasonable arguments on
both sides. Return by value from operator[] enables some potentially
useful iterators, e.g. a random access "iota iterator" (a.k.a
"counting iterator" or "int iterator"). There isn't any obvious way
to do this with return-by-reference, since the reference would be to a
temporary. On the other hand, <tt>reverse_iterator</tt> takes an
arbitrary Random Access Iterator as template argument, and its
operator[] returns by reference. If we decided that the return type
in Table 76 was correct, we would have to change
<tt>reverse_iterator</tt>. This change would probably affect user
code.
</p>
<p>
History: the contradiction between <tt>reverse_iterator</tt> and the
Random Access Iterator requirements has been present from an early
stage. In both the STL proposal adopted by the committee
(N0527==94-0140) and the STL technical report (HPL-95-11 (R.1), by
Stepanov and Lee), the Random Access Iterator requirements say that
operator[]'s return value is "convertible to T". In N0527
reverse_iterator's operator[] returns by value, but in HPL-95-11
(R.1), and in the STL implementation that HP released to the public,
reverse_iterator's operator[] returns by reference. In 1995, the
standard was amended to reflect the contents of HPL-95-11 (R.1). The
original intent for operator[] is unclear.
</p>
<p>
In the long term it may be desirable to add more fine-grained
iterator requirements, so that access method and traversal strategy
can be decoupled. (See "Improved Iterator Categories and
Requirements", N1297 = 01-0011, by Jeremy Siek.) Any decisions
about issue 299 should keep this possibility in mind.
</p>
<p>Further discussion: I propose a compromise between John Potter's
resolution, which requires <tt>T&amp;</tt> as the return type of
<tt>a[n]</tt>, and the current wording, which requires convertible to
<tt>T</tt>. The compromise is to keep the convertible to <tt>T</tt>
for the return type of the expression <tt>a[n]</tt>, but to also add
<tt>a[n] = t</tt> as a valid expression. This compromise "saves" the
common case uses of random access iterators, while at the same time
allowing iterators such as counting iterator and caching file
iterators to remain random access iterators (iterators where the
lifetime of the object returned by <tt>operator*()</tt> is tied to the
lifetime of the iterator).
</p>
<p>
Note that the compromise resolution necessitates a change to
<tt>reverse_iterator</tt>. It would need to use a proxy to support
<tt>a[n] = t</tt>.
</p>
<p>
Note also there is one kind of mutable random access iterator that
will no longer meet the new requirements. Currently, iterators that
return an r-value from <tt>operator[]</tt> meet the requirements for a
mutable random access iterartor, even though the expression <tt>a[n] =
t</tt> will only modify a temporary that goes away. With this proposed
resolution, <tt>a[n] = t</tt> will be required to have the same
operational semantics as <tt>*(a + n) = t</tt>.
</p>
<p><b>Proposed resolution:</b></p>
<p>
In section 24.1.4 [lib.bidirectdional.iterators], change the return
type in table 75 from "convertible to <tt>T</tt>" to
<tt>T&amp;</tt>.
</p>
<p>
In section 24.1.5 [lib.random.access.iterators], change the
operational semantics for <tt>a[n]</tt> to " the r-value of
<tt>a[n]</tt> is equivalent to the r-value of <tt>*(a +
n)</tt>". Add a new row in the table for the expression <tt>a[n] = t</tt>
with a return type of convertible to <tt>T</tt> and operational semantics of
<tt>*(a + n) = t</tt>.
</p>
<p><i>[Lillehammer: Real problem, but should be addressed as part of
iterator redesign]</i></p>
<hr>
<a name="309"><h3>309.&nbsp;Does sentry catch exceptions?</h3></a><p><b>Section:</b>&nbsp;27.6 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.iostream.format"> [lib.iostream.format]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;19 Mar 2001</p>
<p>
The descriptions of the constructors of basic_istream&lt;&gt;::sentry
(27.6.1.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.istream::sentry"> [lib.istream::sentry]</a>) and basic_ostream&lt;&gt;::sentry
(27.6.2.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.ostream::sentry"> [lib.ostream::sentry]</a>) do not explain what the functions do in
case an exception is thrown while they execute. Some current
implementations allow all exceptions to propagate, others catch them
and set ios_base::badbit instead, still others catch some but let
others propagate.
</p>
<p>
The text also mentions that the functions may call setstate(failbit)
(without actually saying on what object, but presumably the stream
argument is meant). That may have been fine for
basic_istream&lt;&gt;::sentry prior to issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#195">195</a>, since
the function performs an input operation which may fail. However,
issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#195">195</a> amends 27.6.1.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.istream::sentry"> [lib.istream::sentry]</a>, p2 to
clarify that the function should actually call setstate(failbit |
eofbit), so the sentence in p3 is redundant or even somewhat
contradictory.
</p>
<p>
The same sentence that appears in 27.6.2.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.ostream::sentry"> [lib.ostream::sentry]</a>, p3
doesn't seem to be very meaningful for basic_istream&lt;&gt;::sentry
which performs no input. It is actually rather misleading since it
would appear to guide library implementers to calling
setstate(failbit) when os.tie()-&gt;flush(), the only called function,
throws an exception (typically, it's badbit that's set in response to
such an event).
</p>
<p><b>Additional comments from Martin, who isn't comfortable with the
current proposed resolution</b> (see c++std-lib-11530)</p>
<p>
The istream::sentry ctor says nothing about how the function
deals with exemptions (27.6.1.1.2, p1 says that the class is
responsible for doing "exception safe"(*) prefix and suffix
operations but it doesn't explain what level of exception
safety the class promises to provide). The mockup example
of a "typical implementation of the sentry ctor" given in
27.6.1.1.2, p6, removed in ISO/IEC 14882:2003, doesn't show
exception handling, either. Since the ctor is not classified
as a formatted or unformatted input function, the text in
27.6.1.1, p1 through p4 does not apply. All this would seem
to suggest that the sentry ctor should not catch or in any
way handle exceptions thrown from any functions it may call.
Thus, the typical implementation of an istream extractor may
look something like [1].
</p>
<p>
The problem with [1] is that while it correctly sets ios::badbit
if an exception is thrown from one of the functions called from
the sentry ctor, if the sentry ctor reaches EOF while extracting
whitespace from a stream that has eofbit or failbit set in
exceptions(), it will cause an ios::failure to be thrown, which
will in turn cause the extractor to set ios::badbit.
</p>
<p>
The only straightforward way to prevent this behavior is to
move the definition of the sentry object in the extractor
above the try block (as suggested by the example in 22.2.8,
p9 and also indirectly supported by 27.6.1.3, p1). See [2].
But such an implementation will allow exceptions thrown from
functions called from the ctor to freely propagate to the
caller regardless of the setting of ios::badbit in the stream
object's exceptions().
</p>
<p>
So since neither [1] nor [2] behaves as expected, the only
possible solution is to have the sentry ctor catch exceptions
thrown from called functions, set badbit, and propagate those
exceptions if badbit is also set in exceptions(). (Another
solution exists that deals with both kinds of sentries, but
the code is non-obvious and cumbersome -- see [3].)
</p>
<p>
Please note that, as the issue points out, current libraries
do not behave consistently, suggesting that implementors are
not quite clear on the exception handling in istream::sentry,
despite the fact that some LWG members might feel otherwise.
(As documented by the parenthetical comment here:
http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1480.html#309)
</p>
<p>
Also please note that those LWG members who in Copenhagen
felt that "a sentry's constructor should not catch exceptions,
because sentries should only be used within (un)formatted input
functions and that exception handling is the responsibility of
those functions, not of the sentries," as noted here
http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2001/n1310.html#309
would in effect be either arguing for the behavior described
in [1] or for extractors implemented along the lines of [3].
</p>
<p>
The original proposed resolution (Revision 25 of the issues
list) clarifies the role of the sentry ctor WRT exception
handling by making it clear that extractors (both library
or user-defined) should be implemented along the lines of
[2] (as opposed to [1]) and that no exception thrown from
the callees should propagate out of either function unless
badbit is also set in exceptions().
</p>
<p>[1] Extractor that catches exceptions thrown from sentry:</p>
<blockquote>
<pre>struct S { long i; };
istream&amp; operator&gt;&gt; (istream &amp;strm, S &amp;s)
{
ios::iostate err = ios::goodbit;
try {
const istream::sentry guard (strm, false);
if (guard) {
use_facet&lt;num_get&lt;char&gt; &gt;(strm.getloc ())
.get (istreambuf_iterator&lt;char&gt;(strm),
istreambuf_iterator&lt;char&gt;(),
strm, err, s.i);
}
}
catch (...) {
bool rethrow;
try {
strm.setstate (ios::badbit);
rethrow = false;
}
catch (...) {
rethrow = true;
}
if (rethrow)
throw;
}
if (err)
strm.setstate (err);
return strm;
}
</pre>
</blockquote>
<p>[2] Extractor that propagates exceptions thrown from sentry:</p>
<blockquote>
<pre>istream&amp; operator&gt;&gt; (istream &amp;strm, S &amp;s)
{
istream::sentry guard (strm, false);
if (guard) {
ios::iostate err = ios::goodbit;
try {
use_facet&lt;num_get&lt;char&gt; &gt;(strm.getloc ())
.get (istreambuf_iterator&lt;char&gt;(strm),
istreambuf_iterator&lt;char&gt;(),
strm, err, s.i);
}
catch (...) {
bool rethrow;
try {
strm.setstate (ios::badbit);
rethrow = false;
}
catch (...) {
rethrow = true;
}
if (rethrow)
throw;
}
if (err)
strm.setstate (err);
}
return strm;
}
</pre>
</blockquote>
<p>
[3] Extractor that catches exceptions thrown from sentry
but doesn't set badbit if the exception was thrown as a
result of a call to strm.clear().
</p>
<blockquote>
<pre>istream&amp; operator&gt;&gt; (istream &amp;strm, S &amp;s)
{
const ios::iostate state = strm.rdstate ();
const ios::iostate except = strm.exceptions ();
ios::iostate err = std::ios::goodbit;
bool thrown = true;
try {
const istream::sentry guard (strm, false);
thrown = false;
if (guard) {
use_facet&lt;num_get&lt;char&gt; &gt;(strm.getloc ())
.get (istreambuf_iterator&lt;char&gt;(strm),
istreambuf_iterator&lt;char&gt;(),
strm, err, s.i);
}
}
catch (...) {
if (thrown &amp;&amp; state &amp; except)
throw;
try {
strm.setstate (ios::badbit);
thrown = false;
}
catch (...) {
thrown = true;
}
if (thrown)
throw;
}
if (err)
strm.setstate (err);
return strm;
}
</pre>
</blockquote>
<p>
[Pre-Berlin] Reopened at the request of Paolo Carlini and Steve Clamage.
</p>
<p>
[Pre-Portland] A relevant newsgroup post:
</p>
<p>
The current proposed resolution of issue #309
(http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#309) is
unacceptable. I write commerical software and coding around this
makes my code ugly, non-intuitive, and requires comments referring
people to this very issue. Following is the full explanation of my
experience.
</p>
<p>
In the course of writing software for commercial use, I constructed
std::ifstream's based on user-supplied pathnames on typical POSIX
systems.
</p>
<p>
It was expected that some files that opened successfully might not read
successfully -- such as a pathname which actually refered to a
directory. Intuitively, I expected the streambuffer underflow() code
to throw an exception in this situation, and recent implementations of
libstdc++'s basic_filebuf do just that (as well as many of my own
custom streambufs).
</p>
<p>
I also intuitively expected that the istream code would convert these
exceptions to the "badbit' set on the stream object, because I had not
requested exceptions. I refer to 27.6.1.1. P4.
</p>
<p>
However, this was not the case on at least two implementations -- if
the first thing I did with an istream was call operator&gt;&gt;( T&amp; ) for T
among the basic arithmetic types and std::string. Looking further I
found that the sentry's constructor was invoking the exception when it
pre-scanned for whitespace, and the extractor function (operator&gt;&gt;())
was not catching exceptions in this situation.
</p>
<p>
So, I was in a situation where setting 'noskipws' would change the
istream's behavior even though no characters (whitespace or not) could
ever be successfully read.
</p>
<p>
Also, calling .peek() on the istream before calling the extractor()
changed the behavior (.peek() had the effect of setting the badbit
ahead of time).
</p>
<p>
I found this all to be so inconsistent and inconvenient for me and my
code design, that I filed a bugzilla entry for libstdc++. I was then
told that the bug cannot be fixed until issue #309 is resolved by the
committee.
</p>
<p><b>Proposed resolution:</b></p>
<p><b>Rationale:</b></p>
<p>The LWG agrees there is minor variation between implementations,
but believes that it doesn't matter. This is a rarely used corner
case. There is no evidence that this has any commercial importance
or that it causes actual portability problems for customers trying
to write code that runs on multiple implementations.</p>
<hr>
<a name="342"><h3>342.&nbsp;seek and eofbit</h3></a><p><b>Section:</b>&nbsp;27.6.1.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.istream.unformatted"> [lib.istream.unformatted]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Howard Hinnant&nbsp; <b>Date:</b>&nbsp;09 Oct 2001</p>
<p>I think we have a defect.</p>
<p>According to lwg issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#60">60</a> which is now a dr, the
description of seekg in 27.6.1.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.istream.unformatted"> [lib.istream.unformatted]</a> paragraph 38 now looks
like:</p>
<blockquote>
Behaves as an unformatted input function (as described in 27.6.1.3,
paragraph 1), except that it does not count the number of characters
extracted and does not affect the value returned by subsequent calls to
gcount(). After constructing a sentry object, if fail() != true,
executes rdbuf()<29>&gt;pubseekpos( pos).
</blockquote>
<p>And according to lwg issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#243">243</a> which is also now a dr,
27.6.1.3, paragraph 1 looks like:</p>
<blockquote>
Each unformatted input function begins execution by constructing an
object of class sentry with the default argument noskipws (second)
argument true. If the sentry object returns true, when converted to a
value of type bool, the function endeavors to obtain the requested
input. Otherwise, if the sentry constructor exits by throwing an
exception or if the sentry object returns false, when converted to a
value of type bool, the function returns without attempting to obtain
any input. In either case the number of extracted characters is set to
0; unformatted input functions taking a character array of non-zero
size as an argument shall also store a null character (using charT())
in the first location of the array. If an exception is thrown during
input then ios::badbit is turned on in *this'ss error state. If
(exception()&amp;badbit)!= 0 then the exception is rethrown. It also counts
the number of characters extracted. If no exception has been thrown it
ends by storing the count in a member object and returning the value
specified. In any event the sentry object is destroyed before leaving
the unformatted input function.
</blockquote>
<p>And finally 27.6.1.1.2/5 says this about sentry:</p>
<blockquote>
If, after any preparation is completed, is.good() is true, ok_ != false
otherwise, ok_ == false.
</blockquote>
<p>
So although the seekg paragraph says that the operation proceeds if
!fail(), the behavior of unformatted functions says the operation
proceeds only if good(). The two statements are contradictory when only
eofbit is set. I don't think the current text is clear which condition
should be respected.
</p>
<p><b>Further discussion from Redmond:</b></p>
<p>PJP: It doesn't seem quite right to say that <tt>seekg</tt> is
"unformatted". That makes specific claims about sentry that
aren't quite appropriate for seeking, which has less fragile failure
modes than actual input. If we do really mean that it's unformatted
input, it should behave the same way as other unformatted input. On
the other hand, "principle of least surprise" is that seeking from EOF
ought to be OK.</p>
<p>
Pre-Berlin: Paolo points out several problems with the proposed resolution in
Ready state:
</p>
<ul>
<li>It should apply to both overloads of seekg.</li>
<li>tellg has similar issues, except that it should not call clear().</li>
<li>The point about clear() seems to apply to seekp().</li>
<li>Depending on the outcome of
<a href="file:///Volumes/Data/lwg/lwg-active.html#419">419</a> if the sentry
sets <tt>failbit</tt> when it finds <tt>eofbit</tt> already set, then
you can never seek away from the end of stream.</li>
</ul>
<p><b>Proposed resolution:</b></p>
<p>Change 27.6.1.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.istream.unformatted"> [lib.istream.unformatted]</a> to:</p>
<blockquote>
Behaves as an unformatted input function (as described in 27.6.1.3,
paragraph 1), except that it does not count the number of characters
extracted, does not affect the value returned by subsequent calls to
gcount(), and does not examine the value returned by the sentry
object. After constructing a sentry object, if <tt>fail() !=
true</tt>, executes <tt>rdbuf()-&gt;pubseekpos(pos)</tt>. In
case of success, the function calls clear().
In case of failure, the function calls <tt>setstate(failbit)</tt>
(which may throw <tt>ios_base::failure</tt>).
</blockquote>
<p><i>[Lillehammer: Matt provided wording.]</i></p>
<p><b>Rationale:</b></p>
<p>In C, fseek does clear EOF. This is probably what most users would
expect. We agree that having eofbit set should not deter a seek,
and that a successful seek should clear eofbit. Note
that <tt>fail()</tt> is true only if <tt>failbit</tt>
or <tt>badbit</tt> is set, so using <tt>!fail()</tt>, rather
than <tt>good()</tt>, satisfies this goal.</p>
<hr>
<a name="382"></a><h3><a name="382">382.&nbsp;codecvt do_in/out result</a></h3><p><b>Section:</b>&nbsp;22.2.1.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-locales.html#lib.locale.codecvt.byname"> [lib.locale.codecvt.byname]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;30 Aug 2002</p>
<p>
It seems that the descriptions of codecvt do_in() and do_out() leave
sufficient room for interpretation so that two implementations of
codecvt may not work correctly with the same filebuf. Specifically,
the following seems less than adequately specified:
</p>
<ol>
<li>
the conditions under which the functions terminate
</li>
<li>
precisely when the functions return ok
</li>
<li>
precisely when the functions return partial
</li>
<li>
the full set of conditions when the functions return error
</li>
</ol>
<ol>
<li>
<font color="red">22.2.1.5.2</font>, p2 says this about the effects of the
function: ...Stops if it encounters a character it cannot
convert... This assumes that there *is* a character to
convert. What happens when there is a sequence that doesn't form a
valid source character, such as an unassigned or invalid UNICODE
character, or a sequence that cannot possibly form a character
(e.g., the sequence "\xc0\xff" in UTF-8)?
</li>
<li>
Table 53 says that the function returns codecvt_base::ok
to indicate that the function(s) "completed the conversion."
Suppose that the source sequence is "\xc0\x80" in UTF-8,
with from pointing to '\xc0' and (from_end==from + 1).
It is not clear whether the return value should be ok
or partial (see below).
</li>
<li>
Table 53 says that the function returns codecvt_base::partial
if "not all source characters converted." With the from pointers
set up the same way as above, it is not clear whether the return
value should be partial or ok (see above).
</li>
<li>
Table 53, in the row describing the meaning of error mistakenly
refers to a "from_type" character, without the symbol from_type
having been defined. Most likely, the word "source" character
is intended, although that is not sufficient. The functions
may also fail when they encounter an invalid source sequence
that cannot possibly form a valid source character (e.g., as
explained in bullet 1 above).
</li>
</ol>
<p>
Finally, the conditions described at the end of <font color="red">22.2.1.5.2</font>, p4 don't seem to be possible:
</p>
<blockquote>
"A return value of partial, if (from_next == from_end),
indicates that either the destination sequence has not
absorbed all the available destination elements, or that
additional source elements are needed before another
destination element can be produced."
</blockquote>
<p>
If the value is partial, it's not clear to me that (from_next
==from_end) could ever hold if there isn't enough room
in the destination buffer. In order for (from_next==from_end) to
hold, all characters in that range must have been successfully
converted (according to <font color="red">22.2.1.5.2</font>, p2) and since there are no
further source characters to convert, no more room in the
destination buffer can be needed.
</p>
<p>
It's also not clear to me that (from_next==from_end) could ever
hold if additional source elements are needed to produce another
destination character (not element as incorrectly stated in the
text). partial is returned if "not all source characters have
been converted" according to Table 53, which also implies that
(from_next==from) does NOT hold.
</p>
<p>
Could it be that the intended qualifying condition was actually
(from_next != from_end), i.e., that the sentence was supposed
to read
</p>
<blockquote>
"A return value of partial, if (from_next != from_end),..."
</blockquote>
<p>
which would make perfect sense, since, as far as I understand it,
partial can only occur if (from_next != from_end)?
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Lillehammer: Defer for the moment, but this really needs to be
fixed. Right now, the description of codecvt is too vague for it to
be a useful contract between providers and clients of codecvt
facets. (Note that both vendors and users can be both providers and
clients of codecvt facets.) The major philosophical issue is whether
the standard should only describe mappings that take a single wide
character to multiple narrow characters (and vice versa), or whether
it should describe fully general N-to-M conversions. When the
original standard was written only the former was contemplated, but
today, in light of the popularity of utf8 and utf16, that doesn't
seem sufficient for C++0x. Bill supports general N-to-M conversions;
we need to make sure Martin and Howard agree.]</i></p>
<hr>
<a name="385"><h3>385.&nbsp;Does call by value imply the CopyConstructible requirement?</h3></a><p><b>Section:</b>&nbsp;17 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-intro.html#lib.library"> [lib.library]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;23 Oct 2002</p>
<p>
Many function templates have parameters that are passed by value;
a typical example is <tt>find_if</tt>'s <i>pred</i> parameter in
25.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-algorithms.html#lib.alg.find"> [lib.alg.find]</a>. Are the corresponding template parameters
(<tt>Predicate</tt> in this case) implicitly required to be
CopyConstructible, or does that need to be spelled out explicitly?
</p>
<p>
This isn't quite as silly a question as it might seem to be at first
sight. If you call <tt>find_if</tt> in such a way that template
argument deduction applies, then of course you'll get call by value
and you need to provide a copy constructor. If you explicitly provide
the template arguments, however, you can force call by reference by
writing something like <tt>find_if&lt;my_iterator,
my_predicate&amp;&gt;</tt>. The question is whether implementation
are required to accept this, or whether this is ill-formed because
my_predicate&amp; is not CopyConstructible.
</p>
<p>
The scope of this problem, if it is a problem, is unknown. Function
object arguments to generic algorithms in clauses 25 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-algorithms.html#lib.algorithms"> [lib.algorithms]</a>
and 26 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.numerics"> [lib.numerics]</a> are obvious examples. A review of the whole
library is necessary.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[
This is really two issues. First, predicates are typically passed by
value but we don't say they must be Copy Constructible. They should
be. Second: is specialization allowed to transform value arguments
into references? References aren't copy constructible, so this should
not be allowed.
]</i></p>
<hr>
<a name="387"><h3>387.&nbsp;std::complex over-encapsulated</h3></a><p><b>Section:</b>&nbsp;26.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.complex.numbers"> [lib.complex.numbers]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Gabriel Dos Reis&nbsp; <b>Date:</b>&nbsp;8 Nov 2002</p>
<p>
The absence of explicit description of std::complex&lt;T&gt; layout
makes it imposible to reuse existing software developed in traditional
languages like Fortran or C with unambigous and commonly accepted
layout assumptions. There ought to be a way for practitioners to
predict with confidence the layout of std::complex&lt;T&gt; whenever T
is a numerical datatype. The absence of ways to access individual
parts of a std::complex&lt;T&gt; object as lvalues unduly promotes
severe pessimizations. For example, the only way to change,
independently, the real and imaginary parts is to write something like
</p>
<pre>complex&lt;T&gt; z;
// ...
// set the real part to r
z = complex&lt;T&gt;(r, z.imag());
// ...
// set the imaginary part to i
z = complex&lt;T&gt;(z.real(), i);
</pre>
<p>
At this point, it seems appropriate to recall that a complex number
is, in effect, just a pair of numbers with no particular invariant to
maintain. Existing practice in numerical computations has it that a
complex number datatype is usually represented by Cartesian
coordinates. Therefore the over-encapsulation put in the specification
of std::complex&lt;&gt; is not justified.
</p>
<p><b>Proposed resolution:</b></p>
<p>Add the following requirements to 26.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.complex.numbers"> [lib.complex.numbers]</a> as 26.3/4:</p>
<blockquote>
<p>If z is an lvalue expression of type cv std::complex&lt;T&gt; then</p>
<ul>
<li>the expression reinterpret_cast&lt;cv T(&amp;)[2]&gt;(z)
is well-formed; and</li>
<li>reinterpret_cast&lt;cvT(&amp;)[2]&gt;(z)[0]designates the
real part of z; and</li>
<li>reinterpret_cast&lt;cvT(&amp;)[2]&gt;(z)[1]designates the
imaginary part of z.</li>
</ul>
<p>
Moreover, if a is an expression of pointer type cv complex&lt;T&gt;*
and the expression a[i] is well-defined for an integer expression
i then:
</p>
<ul>
<li>reinterpret_cast&lt;cvT*&gt;(a)[2+i] designates the real
part of a[i]; and</li>
<li>reinterpret_cast&lt;cv T*&gt;(a)[2+i+1] designates the
imaginary part of a[i].</li>
</ul>
</blockquote>
<p>In the header synopsis in 26.3.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.complex.synopsis"> [lib.complex.synopsis]</a>, replace</p>
<pre> template&lt;class T&gt; T real(const complex&lt;T&gt;&amp;);
template&lt;class T&gt; T imag(const complex&lt;T&gt;&amp;);
</pre>
<p>with</p>
<pre> template&lt;class T&gt; const T&amp; real(const complex&lt;T&gt;&amp;);
template&lt;class T&gt; T&amp; real( complex&lt;T&gt;&amp;);
template&lt;class T&gt; const T&amp; imag(const complex&lt;T&gt;&amp;);
template&lt;class T&gt; T&amp; imag( complex&lt;T&gt;&amp;);
</pre>
<p>In 26.3.7 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.complex.value.ops"> [lib.complex.value.ops]</a> paragraph 1, change</p>
<pre> template&lt;class T&gt; T real(const complex&lt;T&gt;&amp;);
</pre>
<p>to</p>
<pre> template&lt;class T&gt; const T&amp; real(const complex&lt;T&gt;&amp;);
template&lt;class T&gt; T&amp; real( complex&lt;T&gt;&amp;);
</pre>
<p>and change the <b>Returns</b> clause to "<b>Returns:</b> The real
part of <i>x</i></p>.
<p>In 26.3.7 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.complex.value.ops"> [lib.complex.value.ops]</a> paragraph 2, change</p>
<pre> template&lt;class T&gt; T imag(const complex&lt;T&gt;&amp;);
</pre>
<p>to</p>
<pre> template&lt;class T&gt; const T&amp; imag(const complex&lt;T&gt;&amp;);
template&lt;class T&gt; T&amp; imag( complex&lt;T&gt;&amp;);
</pre>
<p>and change the <b>Returns</b> clause to "<b>Returns:</b> The imaginary
part of <i>x</i></p>.
<p><i>[Kona: The layout guarantee is absolutely necessary for C
compatibility. However, there was disagreement about the other part
of this proposal: retrieving elements of the complex number as
lvalues. An alternative: continue to have real() and imag() return
rvalues, but add set_real() and set_imag(). Straw poll: return
lvalues - 2, add setter functions - 5. Related issue: do we want
reinterpret_cast as the interface for converting a complex to an
array of two reals, or do we want to provide a more explicit way of
doing it? Howard will try to resolve this issue for the next
meeting.]</i></p>
<p><i>[pre-Sydney: Howard summarized the options in n1589.]</i></p>
<p><b>Rationale:</b></p>
<p>The LWG believes that C99 compatibility would be enough
justification for this change even without other considerations. All
existing implementations already have the layout proposed here.</p>
<hr>
<a name="394"><h3>394.&nbsp;behavior of formatted output on failure</h3></a><p><b>Section:</b>&nbsp;27.6.2.5.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.ostream.formatted.reqmts"> [lib.ostream.formatted.reqmts]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;27 Dec 2002</p>
<p>
There is a contradiction in Formatted output about what bit is
supposed to be set if the formatting fails. On sentence says it's
badbit and another that it's failbit.
</p>
<p>
27.6.2.5.1, p1 says in the Common Requirements on Formatted output
functions:
</p><pre> ... If the generation fails, then the formatted output function
does setstate(ios::failbit), which might throw an exception.
</pre>
<p></p>
<p>
27.6.2.5.2, p1 goes on to say this about Arithmetic Inserters:
</p>
<p>
... The formatting conversion occurs as if it performed the
following code fragment:
</p>
<p>
</p><pre> bool failed =
use_facet&lt;num_put&lt;charT,ostreambuf_iterator&lt;charT,traits&gt;
&gt; &gt;
(getloc()).put(*this, *this, fill(), val). failed();
... If failed is true then does setstate(badbit) ...
</pre>
<p></p>
<p>
The original intent of the text, according to Jerry Schwarz (see
c++std-lib-10500), is captured in the following paragraph:
</p>
<p>
In general "badbit" should mean that the stream is unusable because
of some underlying failure, such as disk full or socket closure;
"failbit" should mean that the requested formatting wasn't possible
because of some inconsistency such as negative widths. So typically
if you clear badbit and try to output something else you'll fail
again, but if you clear failbit and try to output something else
you'll succeed.
</p>
<p>
In the case of the arithmetic inserters, since num_put cannot
report failure by any means other than exceptions (in response
to which the stream must set badbit, which prevents the kind of
recoverable error reporting mentioned above), the only other
detectable failure is if the iterator returned from num_put
returns true from failed().
</p>
<p>
Since that can only happen (at least with the required iostream
specializations) under such conditions as the underlying failure
referred to above (e.g., disk full), setting badbit would seem
to be the appropriate response (indeed, it is required in
27.6.2.5.2, p1). It follows that failbit can never be directly
set by the arithmetic (it can only be set by the sentry object
under some unspecified conditions).
</p>
<p>
The situation is different for other formatted output functions
which can fail as a result of the streambuf functions failing
(they may do so by means other than exceptions), and which are
then required to set failbit.
</p>
<p>
The contradiction, then, is that ostream::operator&lt;&lt;(int) will
set badbit if the disk is full, while operator&lt;&lt;(ostream&amp;,
char) will set failbit under the same conditions. To make the behavior
consistent, the Common requirements sections for the Formatted output
functions should be changed as proposed below.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Kona: There's agreement that this is a real issue. What we
decided at Kona: 1. An error from the buffer (which can be detected
either directly from streambuf's member functions or by examining a
streambuf_iterator) should always result in badbit getting set.
2. There should never be a circumstance where failbit gets set.
That represents a formatting error, and there are no circumstances
under which the output facets are specified as signaling a
formatting error. (Even more so for string output that for numeric
because there's nothing to format.) If we ever decide to make it
possible for formatting errors to exist then the facets can signal
the error directly, and that should go in clause 22, not clause 27.
3. The phrase "if generation fails" is unclear and should be
eliminated. It's not clear whether it's intended to mean a buffer
error (e.g. a full disk), a formatting error, or something else.
Most people thought it was supposed to refer to buffer errors; if
so, we should say so. Martin will provide wording.]</i></p>
<p><b>Rationale:</b></p>
<hr>
<a name="396"><h3>396.&nbsp;what are characters zero and one</h3></a><p><b>Section:</b>&nbsp;23.3.5.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.bitset.cons"> [lib.bitset.cons]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;5 Jan 2003</p>
<p>
23.3.5.1, p6 [lib.bitset.cons] talks about a generic character
having the value of 0 or 1 but there is no definition of what
that means for charT other than char and wchar_t. And even for
those two types, the values 0 and 1 are not actually what is
intended -- the values '0' and '1' are. This, along with the
converse problem in the description of to_string() in 23.3.5.2,
p33, looks like a defect remotely related to DR 303.
</p>
<p>
http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-defects.html#303
</p>
<pre>23.3.5.1:
-6- An element of the constructed string has value zero if the
corresponding character in str, beginning at position pos,
is 0. Otherwise, the element has the value one.
</pre>
<pre>23.3.5.2:
-33- Effects: Constructs a string object of the appropriate
type and initializes it to a string of length N characters.
Each character is determined by the value of its
corresponding bit position in *this. Character position N
?- 1 corresponds to bit position zero. Subsequent decreasing
character positions correspond to increasing bit positions.
Bit value zero becomes the character 0, bit value one becomes
the character 1.
</pre>
<p>
Also note the typo in 23.3.5.1, p6: the object under construction
is a bitset, not a string.
</p>
<p><b>Proposed resolution:</b></p>
<p>Change the constructor's function declaration immediately before
23.3.5.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.bitset.cons"> [lib.bitset.cons]</a> p3 to:</p>
<pre> template &lt;class charT, class traits, class Allocator&gt;
explicit
bitset(const basic_string&lt;charT, traits, Allocator&gt;&amp; str,
typename basic_string&lt;charT, traits, Allocator&gt;::size_type pos = 0,
typename basic_string&lt;charT, traits, Allocator&gt;::size_type n =
basic_string&lt;charT, traits, Allocator&gt;::npos,
charT zero = charT('0'), charT one = charT('1'))
</pre>
<p>Change the first two sentences of 23.3.5.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.bitset.cons"> [lib.bitset.cons]</a> p6 to: "An
element of the constructed string has value 0 if the corresponding
character in <i>str</i>, beginning at position <i>pos</i>,
is <i>zero</i>. Otherwise, the element has the value 1.</p>
<p>Change the text of the second sentence in 23.3.5.1, p5 to read:
"The function then throws invalid_argument if any of the rlen
characters in str beginning at position pos is other than <i>zero</i>
or <i>one</i>. The function uses traits::eq() to compare the character
values."
</p>
<p>Change the declaration of the <tt>to_string</tt> member function
immediately before 23.3.5.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.bitset.members"> [lib.bitset.members]</a> p33 to:</p>
<pre> template &lt;class charT, class traits, class Allocator&gt;
basic_string&lt;charT, traits, Allocator&gt;
to_string(charT zero = charT('0'), charT one = charT('1')) const;
</pre>
<p>Change the last sentence of 23.3.5.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.bitset.members"> [lib.bitset.members]</a> p33 to: "Bit
value 0 becomes the character <tt><i>zero</i></tt>, bit value 1 becomes the
character <tt><i>one</i></tt>.</p>
<p>Change 23.3.5.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.bitset.operators"> [lib.bitset.operators]</a> p8 to:</p>
<p><b>Returns</b>:</p>
<pre> os &lt;&lt; x.template to_string&lt;charT,traits,allocator&lt;charT&gt; &gt;(
use_facet&lt;ctype&lt;charT&gt; &gt;(<i>os</i>.getloc()).widen('0'),
use_facet&lt;ctype&lt;charT&gt; &gt;(<i>os</i>.getloc()).widen('1'));
</pre>
<p><b>Rationale:</b></p>
<p>There is a real problem here: we need the character values of '0'
and '1', and we have no way to get them since strings don't have
imbued locales. In principle the "right" solution would be to
provide an extra object, either a ctype facet or a full locale,
which would be used to widen '0' and '1'. However, there was some
discomfort about using such a heavyweight mechanism. The proposed
resolution allows those users who care about this issue to get it
right.</p>
<p>We fix the inserter to use the new arguments. Note that we already
fixed the analogous problem with the extractor in issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#303">303</a>.</p>
<hr>
<a name="397"><h3>397.&nbsp;ostream::sentry dtor throws exceptions</h3></a><p><b>Section:</b>&nbsp;27.6.2.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.ostream::sentry"> [lib.ostream::sentry]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;5 Jan 2003</p>
<p>
17.4.4.8, p3 prohibits library dtors from throwing exceptions.
</p>
<p>
27.6.2.3, p4 says this about the ostream::sentry dtor:
</p>
<pre> -4- If ((os.flags() &amp; ios_base::unitbuf) &amp;&amp; !uncaught_exception())
is true, calls os.flush().
</pre>
<p>
27.6.2.6, p7 that describes ostream::flush() says:
</p>
<pre> -7- If rdbuf() is not a null pointer, calls rdbuf()-&gt;pubsync().
If that function returns ?-1 calls setstate(badbit) (which
may throw ios_base::failure (27.4.4.3)).
</pre>
<p>
That seems like a defect, since both pubsync() and setstate() can
throw an exception.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[
The contradiction is real. Clause 17 says destructors may never
throw exceptions, and clause 27 specifies a destructor that does
throw. In principle we might change either one. We're leaning
toward changing clause 17: putting in an "unless otherwise specified"
clause, and then putting in a footnote saying the sentry destructor
is the only one that can throw. PJP suggests specifying that
sentry::~sentry() should internally catch any exceptions it might cause.
]</i></p>
<hr>
<a name="398"><h3>398.&nbsp;effects of end-of-file on unformatted input functions</h3></a><p><b>Section:</b>&nbsp;27.6.2.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.ostream::sentry"> [lib.ostream::sentry]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;5 Jan 2003</p>
<p>
While reviewing unformatted input member functions of istream
for their behavior when they encounter end-of-file during input
I found that the requirements vary, sometimes unexpectedly, and
in more than one case even contradict established practice (GNU
libstdc++ 3.2, IBM VAC++ 6.0, STLPort 4.5, SunPro 5.3, HP aCC
5.38, Rogue Wave libstd 3.1, and Classic Iostreams).
</p>
<p>
The following unformatted input member functions set eofbit if they
encounter an end-of-file (this is the expected behavior, and also
the behavior of all major implementations):
</p>
<p>
</p><pre> basic_istream&lt;charT, traits&gt;&amp;
get (char_type*, streamsize, char_type);
</pre>
<p></p>
<p>
Also sets failbit if it fails to extract any characters.
</p>
<p>
</p><pre> basic_istream&lt;charT, traits&gt;&amp;
get (char_type*, streamsize);
</pre>
<p></p>
<p>
Also sets failbit if it fails to extract any characters.
</p>
<p>
</p><pre> basic_istream&lt;charT, traits&gt;&amp;
getline (char_type*, streamsize, char_type);
</pre>
<p></p>
<p>
Also sets failbit if it fails to extract any characters.
</p>
<p>
</p><pre> basic_istream&lt;charT, traits&gt;&amp;
getline (char_type*, streamsize);
</pre>
<p></p>
<p>
Also sets failbit if it fails to extract any characters.
</p>
<p>
</p><pre> basic_istream&lt;charT, traits&gt;&amp;
ignore (int, int_type);
</pre>
<p></p>
<p>
</p><pre> basic_istream&lt;charT, traits&gt;&amp;
read (char_type*, streamsize);
</pre>
<p></p>
<p>
Also sets failbit if it encounters end-of-file.
</p>
<p>
</p><pre> streamsize readsome (char_type*, streamsize);
</pre>
<p></p>
<p>
The following unformated input member functions set failbit but
not eofbit if they encounter an end-of-file (I find this odd
since the functions make it impossible to distinguish a general
failure from a failure due to end-of-file; the requirement is
also in conflict with all major implementation which set both
eofbit and failbit):
</p>
<p>
</p><pre> int_type get();
</pre>
<p></p>
<p>
</p><pre> basic_istream&lt;charT, traits&gt;&amp;
get (char_type&amp;);
</pre>
<p></p>
<p>
These functions only set failbit of they extract no characters,
otherwise they don't set any bits, even on failure (I find this
inconsistency quite unexpected; the requirement is also in
conflict with all major implementations which set eofbit
whenever they encounter end-of-file):
</p>
<p>
</p><pre> basic_istream&lt;charT, traits&gt;&amp;
get (basic_streambuf&lt;charT, traits&gt;&amp;, char_type);
</pre>
<p></p>
<p>
</p><pre> basic_istream&lt;charT, traits&gt;&amp;
get (basic_streambuf&lt;charT, traits&gt;&amp;);
</pre>
<p></p>
<p>
This function sets no bits (all implementations except for
STLport and Classic Iostreams set eofbit when they encounter
end-of-file):
</p>
<p>
</p><pre> int_type peek ();
</pre>
<p></p>
<p><b>Proposed resolution:</b></p>
<p>Informally, what we want is a global statement of intent saying
that eofbit gets set if we trip across EOF, and then we can take
away the specific wording for individual functions. A full review
is necessary. The wording currently in the standard is a mishmash,
and changing it on an individual basis wouldn't make things better.
Dietmar will do this work.</p>
<hr>
<a name="401"><h3>401.&nbsp; incorrect type casts in table 32 in lib.allocator.requirements</h3></a><p><b>Section:</b>&nbsp;20.1.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.default.con.req"> [lib.default.con.req]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Markus Mauhart&nbsp; <b>Date:</b>&nbsp;27 Feb 2003</p>
<p>
I think that in par2 of 20.1.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.default.con.req"> [lib.default.con.req]</a> the last two
lines of table 32 contain two incorrect type casts. The lines are ...
</p>
<pre> a.construct(p,t) Effect: new((void*)p) T(t)
a.destroy(p) Effect: ((T*)p)?-&gt;~T()
</pre>
<p>
.... with the prerequisits coming from the preceding two paragraphs, especially
from table 31:
</p>
<pre> alloc&lt;T&gt; a ;// an allocator for T
alloc&lt;T&gt;::pointer p ;// random access iterator
// (may be different from T*)
alloc&lt;T&gt;::reference r = *p;// T&amp;
T const&amp; t ;
</pre>
<p>
For that two type casts ("(void*)p" and "(T*)p") to be well-formed
this would require then conversions to T* and void* for all
alloc&lt;T&gt;::pointer, so it would implicitely introduce extra
requirements for alloc&lt;T&gt;::pointer, additionally to the only
current requirement (being a random access iterator).
</p>
<p><b>Proposed resolution:</b></p>
<p>
"(void*)p" should be replaced with "(void*)&amp;*p" and that
"((T*)p)?-&gt;" should be replaced with "(*p)." or with
"(&amp;*p)-&gt;".
</p>
<p>
Note: Actually I would prefer to replace "((T*)p)?-&gt;dtor_name" with
"p?-&gt;dtor_name", but AFAICS this is not possible cause of an omission
in 13.5.6 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/over.html#over.ref"> [over.ref]</a> (for which I have filed another DR on 29.11.2002).
</p>
<p><i>[Kona: The LWG thinks this is somewhere on the border between
Open and NAD. The intend is clear: <tt>construct</tt> constructs an
object at the location <i>p</i>. It's reading too much into the
description to think that literally calling <tt>new</tt> is
required. Tweaking this description is low priority until we can do
a thorough review of allocators, and, in particular, allocators with
non-default pointer types.]</i></p>
<hr>
<a name="408"><h3>408.&nbsp;Is vector&lt;reverse_iterator&lt;char*&gt; &gt; forbidden?</h3></a><p><b>Section:</b>&nbsp;24.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iterators.html#lib.iterator.requirements"> [lib.iterator.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Nathan Myers&nbsp; <b>Date:</b>&nbsp;3 June 2003</p>
<p>
I've been discussing iterator semantics with Dave Abrahams, and a
surprise has popped up. I don't think this has been discussed before.
</p>
<p>
24.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iterators.html#lib.iterator.requirements"> [lib.iterator.requirements]</a> says that the only operation that can be performed on "singular"
iterator values is to assign a non-singular value to them. (It
doesn't say they can be destroyed, and that's probably a defect.)
Some implementations have taken this to imply that there is no need
to initialize the data member of a reverse_iterator&lt;&gt; in the default
constructor. As a result, code like
</p>
<blockquote>
std::vector&lt;std::reverse_iterator&lt;char*&gt; &gt; v(7);
v.reserve(1000);
</blockquote>
<p>
invokes undefined behavior, because it must default-initialize the
vector elements, and then copy them to other storage. Of course many
other vector operations on these adapters are also left undefined,
and which those are is not reliably deducible from the standard.
</p>
<p>
I don't think that 24.1 was meant to make standard-library iterator
types unsafe. Rather, it was meant to restrict what operations may
be performed by functions which take general user- and standard
iterators as arguments, so that raw pointers would qualify as
iterators. However, this is not clear in the text, others have come
to the opposite conclusion.
</p>
<p>
One question is whether the standard iterator adaptors have defined
copy semantics. Another is whether they have defined destructor
semantics: is
</p>
<blockquote>
{ std::vector&lt;std::reverse_iterator&lt;char*&gt; &gt; v(7); }
</blockquote>
<p>
undefined too?
</p>
<p>
Note this is not a question of whether algorithms are allowed to
rely on copy semantics for arbitrary iterators, just whether the
types we actually supply support those operations. I believe the
resolution must be expressed in terms of the semantics of the
adapter's argument type. It should make clear that, e.g., the
reverse_iterator&lt;T&gt; constructor is actually required to execute
T(), and so copying is defined if the result of T() is copyable.
</p>
<p>
Issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#235">235</a>, which defines reverse_iterator's default
constructor more precisely, has some relevance to this issue.
However, it is not the whole story.
</p>
<p>
The issue was whether
</p>
<blockquote>
reverse_iterator() { }
</blockquote>
<p>
is allowed, vs.
</p>
<blockquote>
reverse_iterator() : current() { }
</blockquote>
<p>
The difference is when T is char*, where the first leaves the member
uninitialized, and possibly equal to an existing pointer value, or
(on some targets) may result in a hardware trap when copied.
</p>
<p>
8.5 paragraph 5 seems to make clear that the second is required to
satisfy DR <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#235">235</a>, at least for non-class Iterator argument
types.
</p>
<p>
But that only takes care of reverse_iterator, and doesn't establish
a policy for all iterators. (The reverse iterator adapter was just
an example.) In particular, does my function
</p>
<blockquote>
template &lt;typename Iterator&gt;
void f() { std::vector&lt;Iterator&gt; v(7); }
</blockquote>
<p>
evoke undefined behavior for some conforming iterator definitions?
I think it does, now, because vector&lt;&gt; will destroy those singular
iterator values, and that's explicitly disallowed.
</p>
<p>
24.1 shouldn't give blanket permission to copy all singular iterators,
because then pointers wouldn't qualify as iterators. However, it
should allow copying of that subset of singular iterator values that
are default-initialized, and it should explicitly allow destroying any
iterator value, singular or not, default-initialized or not.
</p>
<p>Related issue: <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#407">407</a></p>
<p><b>Proposed resolution:</b></p>
<p><i>[
We don't want to require all singular iterators to be copyable,
because that is not the case for pointers. However, default
construction may be a special case. Issue: is it really default
construction we want to talk about, or is it something like value
initialization? We need to check with core to see whether default
constructed pointers are required to be copyable; if not, it would be
wrong to impose so strict a requirement for iterators.
]</i></p>
<hr>
<a name="416"><h3>416.&nbsp;definitions of XXX_MIN and XXX_MAX macros in climits</h3></a><p><b>Section:</b>&nbsp;18.2.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-support.html#lib.c.limits"> [lib.c.limits]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;18 Sep 2003</p>
<p>
Given two overloads of the function foo(), one taking an argument of type
int and the other taking a long, which one will the call foo(LONG_MAX)
resolve to? The expected answer should be foo(long), but whether that
is true depends on the #defintion of the LONG_MAX macro, specifically
its type. This issue is about the fact that the type of these macros
is not actually required to be the same as the the type each respective
limit.
<br>
Section 18.2.2 of the C++ Standard does not specify the exact types of
the XXX_MIN and XXX_MAX macros #defined in the &lt;climits&gt; and &lt;limits.h&gt;
headers such as INT_MAX and LONG_MAX and instead defers to the C standard.
<br>
Section 5.2.4.2.1, p1 of the C standard specifies that "The values [of
these constants] shall be replaced by constant expressions suitable for use
in #if preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX,
the following shall be replaced by expressions that have the same type as
would an expression that is an object of the corresponding type converted
according to the integer promotions."
<br>
The "corresponding type converted according to the integer promotions" for
LONG_MAX is, according to 6.4.4.1, p5 of the C standard, the type of long
converted to the first of the following set of types that can represent it:
int, long int, long long int. So on an implementation where (sizeof(long)
== sizeof(int)) this type is actually int, while on an implementation where
(sizeof(long) &gt; sizeof(int)) holds this type will be long.
<br>
This is not an issue in C since the type of the macro cannot be detected
by any conforming C program, but it presents a portability problem in C++
where the actual type is easily detectable by overload resolution.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Kona: the LWG does not believe this is a defect. The C macro
definitions are what they are; we've got a better
mechanism, <tt>std::numeric_limits</tt>, that is specified more
precisely than the C limit macros. At most we should add a
nonnormative note recommending that users who care about the exact
types of limit quantities should use &lt;limits&gt; instead of
&lt;climits&gt;.]</i></p>
<hr>
<a name="417"><h3>417.&nbsp;what does ctype::do_widen() return on failure</h3></a><p><b>Section:</b>&nbsp;22.2.1.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-locales.html#lib.locale.ctype.virtuals"> [lib.locale.ctype.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;18 Sep 2003</p>
<p>
The Effects and Returns clauses of the do_widen() member function of
the ctype facet fail to specify the behavior of the function on failure.
That the function may not be able to simply cast the narrow character
argument to the type of the result since doing so may yield the wrong value
for some wchar_t encodings. Popular implementations of ctype&lt;wchar_t&gt; that
use mbtowc() and UTF-8 as the native encoding (e.g., GNU glibc) will fail
when the argument's MSB is set. There is no way for the the rest of locale
and iostream to reliably detect this failure.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Kona: This is a real problem. Widening can fail. It's unclear
what the solution should be. Returning WEOF works for the wchar_t
specialization, but not in general. One option might be to add a
default, like <i>narrow</i>. But that's an incompatible change.
Using <i>traits::eof</i> might seem like a good idea, but facets
don't have access to traits (a recurring problem). We could
have <i>widen</i> throw an exception, but that's a scary option;
existing library components aren't written with the assumption
that <i>widen</i> can throw.]</i></p>
<hr>
<a name="418"><h3>418.&nbsp;exceptions thrown during iostream cleanup</h3></a><p><b>Section:</b>&nbsp;27.4.2.1.6 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.ios::Init"> [lib.ios::Init]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;18 Sep 2003</p>
<p>
The dtor of the ios_base::Init object is supposed to call flush() on the
6 standard iostream objects cout, cerr, clog, wcout, wcerr, and wclog.
This call may cause an exception to be thrown.
</p>
<p>
17.4.4.8, p3 prohibits all library destructors from throwing exceptions.
</p>
<p>
The question is: What should this dtor do if one or more of these calls
to flush() ends up throwing an exception? This can happen quite easily
if one of the facets installed in the locale imbued in the iostream
object throws.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Kona: We probably can't do much better than what we've got, so
the LWG is leaning toward NAD. At the point where the standard
stream objects are being cleaned up, the usual error reporting
mechanism are all unavailable. And exception from flush at this
point will definitely cause problems. A quality implementation
might reasonably swallow the exception, or call abort, or do
something even more drastic.]</i></p>
<hr>
<a name="419"><h3>419.&nbsp;istream extractors not setting failbit if eofbit is already set</h3></a><p><b>Section:</b>&nbsp;27.6.1.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.istream::sentry"> [lib.istream::sentry]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;18 Sep 2003</p>
<p>
27.6.1.1.2, p2 says that istream::sentry ctor prepares for input if is.good()
is true. p4 then goes on to say that the ctor sets the sentry::ok_ member to
true if the stream state is good after any preparation. 27.6.1.2.1, p1 then
says that a formatted input function endeavors to obtain the requested input
if the sentry's operator bool() returns true.
Given these requirements, no formatted extractor should ever set failbit if
the initial stream rdstate() == eofbit. That is contrary to the behavior of
all implementations I tested. The program below prints out
eof = 1, fail = 0
eof = 1, fail = 1
on all of them.
</p>
<pre>
#include &lt;sstream&gt;
#include &lt;cstdio&gt;
int main()
{
std::istringstream strm ("1");
int i = 0;
strm &gt;&gt; i;
std::printf ("eof = %d, fail = %d\n",
!!strm.eof (), !!strm.fail ());
strm &gt;&gt; i;
std::printf ("eof = %d, fail = %d\n",
!!strm.eof (), !!strm.fail ());
}
</pre>
<p>
<br>
Comments from Jerry Schwarz (c++std-lib-11373):
<br>
Jerry Schwarz wrote:
<br>
I don't know where (if anywhere) it says it in the standard, but the
formatted extractors are supposed to set failbit if they don't extract
any characters. If they didn't then simple loops like
<br>
while (cin &gt;&gt; x);
<br>
would loop forever.
<br>
Further comments from Martin Sebor:
<br>
The question is which part of the extraction should prevent this from happening
by setting failbit when eofbit is already set. It could either be the sentry
object or the extractor. It seems that most implementations have chosen to
set failbit in the sentry [...] so that's the text that will need to be
corrected.
</p>
<p>
Pre Berlin: This issue is related to
<a href="file:///Volumes/Data/lwg/lwg-active.html#342">342</a>. If the sentry
sets <tt>failbit</tt> when it finds <tt>eofbit</tt> already set, then
you can never seek away from the end of stream.
</p>
<p><b>Proposed resolution:</b></p>
<p>Kona: Possibly NAD. If eofbit is set then good() will return false. We
then set <i>ok</i> to false. We believe that the sentry's
constructor should always set failbit when <i>ok</i> is false, and
we also think the standard already says that. Possibly it could be
clearer.</p>
<hr>
<a name="421"><h3>421.&nbsp;is basic_streambuf copy-constructible?</h3></a><p><b>Section:</b>&nbsp;27.5.2.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.streambuf.cons"> [lib.streambuf.cons]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;18 Sep 2003</p>
<p>
The reflector thread starting with c++std-lib-11346 notes that the class
template basic_streambuf, along with basic_stringbuf and basic_filebuf,
is copy-constructible but that the semantics of the copy constructors
are not defined anywhere. Further, different implementations behave
differently in this respect: some prevent copy construction of objects
of these types by declaring their copy ctors and assignment operators
private, others exhibit undefined behavior, while others still give
these operations well-defined semantics.
</p>
<p>
Note that this problem doesn't seem to be isolated to just the three
types mentioned above. A number of other types in the library section
of the standard provide a compiler-generated copy ctor and assignment
operator yet fail to specify their semantics. It's believed that the
only types for which this is actually a problem (i.e. types where the
compiler-generated default may be inappropriate and may not have been
intended) are locale facets. See issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-closed.html#439">439</a>.
</p>
<p><b>Proposed resolution:</b></p>
<p>
27.5.2 [lib.streambuf]: Add into the synopsis, public section, just above the destructor declaration:
</p>
<blockquote>
<pre>basic_streambuf(const basic_streambuf&amp; sb);
basic_streambuf&amp; operator=(const basic_streambuf&amp; sb);
</pre>
</blockquote>
<p>Insert after 27.5.2.1, paragraph 2:</p>
<blockquote>
<pre>basic_streambuf(const basic_streambuf&amp; sb);
</pre>
<p>Constructs a copy of sb.</p>
<p>Postcondtions:</p>
<pre> eback() == sb.eback()
gptr() == sb.gptr()
egptr() == sb.egptr()
pbase() == sb.pbase()
pptr() == sb.pptr()
epptr() == sb.epptr()
getloc() == sb.getloc()
</pre>
<pre>basic_streambuf&amp; operator=(const basic_streambuf&amp; sb);
</pre>
<p>Assigns the data members of sb to this.</p>
<p>Postcondtions:</p>
<pre> eback() == sb.eback()
gptr() == sb.gptr()
egptr() == sb.egptr()
pbase() == sb.pbase()
pptr() == sb.pptr()
epptr() == sb.epptr()
getloc() == sb.getloc()
</pre>
<p>Returns: *this.</p>
</blockquote>
<p>27.7.1 [lib.stringbuf]:</p>
<b>Option A:</b>
<blockquote>
<p>Insert into the basic_stringbuf synopsis in the private section:</p>
<pre>basic_stringbuf(const basic_stringbuf&amp;); // not defined
basic_stringbuf&amp; operator=(const basic_stringbuf&amp;); // not defined
</pre>
</blockquote>
<b>Option B:</b>
<blockquote>
<p>Insert into the basic_stringbuf synopsis in the public section:</p>
<pre>basic_stringbuf(const basic_stringbuf&amp; sb);
basic_stringbuf&amp; operator=(const basic_stringbuf&amp; sb);
</pre>
<p>27.7.1.1, insert after paragraph 4:</p>
<pre>basic_stringbuf(const basic_stringbuf&amp; sb);</pre>
<p>
Constructs an independent copy of sb as if with sb.str(), and with the openmode that sb was constructed with.
</p>
<p>Postcondtions: </p>
<pre> str() == sb.str()
gptr() - eback() == sb.gptr() - sb.eback()
egptr() - eback() == sb.egptr() - sb.eback()
pptr() - pbase() == sb.pptr() - sb.pbase()
getloc() == sb.getloc()
</pre>
<p>
Note: The only requirement on epptr() is that it point beyond the
initialized range if an output sequence exists. There is no requirement
that epptr() - pbase() == sb.epptr() - sb.pbase().
</p>
<pre>basic_stringbuf&amp; operator=(const basic_stringbuf&amp; sb);</pre>
<p>After assignment the basic_stringbuf has the same state as if it
were initially copy constructed from sb, except that the
basic_stringbuf is allowed to retain any excess capacity it might have,
which may in turn effect the value of epptr().
</p>
</blockquote>
<p>27.8.1.1 [lib.filebuf]</p>
<p>Insert at the bottom of the basic_filebuf synopsis:</p>
<blockquote>
<pre>private:
basic_filebuf(const basic_filebuf&amp;); // not defined
basic_filebuf&amp; operator=(const basic_filebuf&amp;); // not defined
</pre>
</blockquote>
<p><i>[Kona: this is an issue for basic_streambuf itself and for its
derived classes. We are leaning toward allowing basic_streambuf to
be copyable, and specifying its precise semantics. (Probably the
obvious: copying the buffer pointers.) We are less sure whether
the streambuf derived classes should be copyable. Howard will
write up a proposal.]</i></p>
<p><i>[Sydney: Dietmar presented a new argument against basic_streambuf
being copyable: it can lead to an encapsulation violation. Filebuf
inherits from streambuf. Now suppose you inhert a my_hijacking_buf
from streambuf. You can copy the streambuf portion of a filebuf to a
my_hijacking_buf, giving you access to the pointers into the
filebuf's internal buffer. Perhaps not a very strong argument, but
it was strong enough to make people nervous. There was weak
preference for having streambuf not be copyable. There was weak
preference for having stringbuf not be copyable even if streambuf
is. Move this issue to open for now.
]</i></p>
<p><b>Rationale:</b></p>
<p>
27.5.2 [lib.streambuf]: The proposed basic_streambuf copy constructor
and assignment operator are the same as currently implied by the lack
of declarations: public and simply copies the data members. This
resolution is not a change but a clarification of the current
standard.
</p>
<p>
27.7.1 [lib.stringbuf]: There are two reasonable options: A) Make
basic_stringbuf not copyable. This is likely the status-quo of
current implementations. B) Reasonable copy semantics of
basic_stringbuf can be defined and implemented. A copyable
basic_streambuf is arguably more useful than a non-copyable one. This
should be considered as new functionality and not the fixing of a
defect. If option B is chosen, ramifications from issue 432 are taken
into account.
</p>
<p>
27.8.1.1 [lib.filebuf]: There are no reasonable copy semantics for
basic_filebuf.
</p>
<hr>
<a name="422"><h3>422.&nbsp;explicit specializations of member functions of class templates</h3></a><p><b>Section:</b>&nbsp;17.4.3.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-intro.html#lib.reserved.names"> [lib.reserved.names]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;18 Sep 2003</p>
<p>
It has been suggested that 17.4.3.1, p1 may or may not allow programs to
explicitly specialize members of standard templates on user-defined types.
The answer to the question might have an impact where library requirements
are given using the "as if" rule. I.e., if programs are allowed to specialize
member functions they will be able to detect an implementation's strict
conformance to Effects clauses that describe the behavior of the function
in terms of the other member function (the one explicitly specialized by
the program) by relying on the "as if" rule.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Add the following sentence immediately after the text of 17.4.3.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-intro.html#lib.reserved.names"> [lib.reserved.names]</a>, p1:
</p>
<blockquote>
The behavior of a program that declares explicit specializations
of any members of class templates or explicit specializations of
any member templates of classes or class templates defined in
this library is undefined.
</blockquote>
<p><i>[Kona: straw poll was 6-1 that user programs should not be
allowed to specialize individual member functions of standard
library class templates, and that doing so invokes undefined
behavior. Post-Kona: Martin provided wording.]</i></p>
<p><i>[Sydney: The LWG agrees that the standard shouldn't permit users
to specialize individual member functions unless they specialize the
whole class, but we're not sure these words say what we want them to;
they could be read as prohibiting the specialization of any standard
library class templates. We need to consult with CWG to make sure we
use the right wording.]</i></p>
<hr>
<a name="423"><h3>423.&nbsp;effects of negative streamsize in iostreams</h3></a><p><b>Section:</b>&nbsp;27 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.input.output"> [lib.input.output]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;18 Sep 2003</p>
<p>
A third party test suite tries to exercise istream::ignore(N) with
a negative value of N and expects that the implementation will treat
N as if it were 0. Our implementation asserts that (N &gt;= 0) holds and
aborts the test.
</p>
<p>
I can't find anything in section 27 that prohibits such values but I don't
see what the effects of such calls should be, either (this applies to
a number of unformatted input functions as well as some member functions
of the basic_streambuf template).
</p>
<p><b>Proposed resolution:</b></p>
<p>
I propose that we add to each function in clause 27 that takes an argument,
say N, of type streamsize a Requires clause saying that "N &gt;= 0." The intent
is to allow negative streamsize values in calls to precision() and width()
but disallow it in calls to streambuf::sgetn(), istream::ignore(), or
ostream::write().
</p>
<p><i>[Kona: The LWG agreed that this is probably what we want. However, we
need a review to find all places where functions in clause 27 take
arguments of type streamsize that shouldn't be allowed to go
negative. Martin will do that review.]</i></p>
<hr>
<a name="424"><h3>424.&nbsp;normative notes</h3></a><p><b>Section:</b>&nbsp;17.3.1.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-intro.html#lib.structure.summary"> [lib.structure.summary]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;18 Sep 2003</p>
<p>
The text in 17.3.1.1, p1 says:
<br>
"Paragraphs labelled "Note(s):" or "Example(s):" are informative, other
paragraphs are normative."
<br>
The library section makes heavy use of paragraphs labeled "Notes(s),"
some of which are clearly intended to be normative (see list 1), while
some others are not (see list 2). There are also those where the intent
is not so clear (see list 3).
<br>
List 1 -- Examples of (presumably) normative Notes:
<br>
20.4.1.1, p3, 20.4.1.1, p10, 21.3.1, p11, 22.1.1.2, p11, 23.2.1.3, p2,
25.3.7, p3, 26.2.6, p14a, 27.5.2.4.3, p7.
<br>
List 2 -- Examples of (presumably) informative Notes:
<br>
18.4.1.3, p3, 21.3.5.6, p14, 22.2.1.5.2, p3, 25.1.1, p4, 26.2.5, p1,
27.4.2.5, p6.
<br>
List 3 -- Examples of Notes that are not clearly either normative
or informative:
<br>
22.1.1.2, p8, 22.1.1.5, p6, 27.5.2.4.5, p4.
<br>
None of these lists is meant to be exhaustive.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Definitely a real problem. The big problem is there's material
that doesn't quite fit any of the named paragraph categories
(e.g. <b>Effects</b>). Either we need a new kind of named
paragraph, or we need to put more material in unnamed paragraphs
jsut after the signature. We need to talk to the Project Editor
about how to do this.
]</i></p>
<hr>
<a name="427"><h3>427.&nbsp;stage 2 and rationale of DR 221</h3></a><p><b>Section:</b>&nbsp;22.2.2.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-locales.html#lib.facet.num.get.virtuals"> [lib.facet.num.get.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;18 Sep 2003</p>
<p>
The requirements specified in Stage 2 and reiterated in the rationale
of DR 221 (and echoed again in DR 303) specify that num_get&lt;charT&gt;::
do_get() compares characters on the stream against the widened elements
of "012...abc...ABCX+-"
</p>
<p>
An implementation is required to allow programs to instantiate the num_get
template on any charT that satisfies the requirements on a user-defined
character type. These requirements do not include the ability of the
character type to be equality comparable (the char_traits template must
be used to perform tests for equality). Hence, the num_get template cannot
be implemented to support any arbitrary character type. The num_get template
must either make the assumption that the character type is equality-comparable
(as some popular implementations do), or it may use char_traits&lt;charT&gt; to do
the comparisons (some other popular implementations do that). This diversity
of approaches makes it difficult to write portable programs that attempt to
instantiate the num_get template on user-defined types.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Kona: the heart of the problem is that we're theoretically
supposed to use traits classes for all fundamental character
operations like assignment and comparison, but facets don't have
traits parameters. This is a fundamental design flaw and it
appears all over the place, not just in this one place. It's not
clear what the correct solution is, but a thorough review of facets
and traits is in order. The LWG considered and rejected the
possibility of changing numeric facets to use narrowing instead of
widening. This may be a good idea for other reasons (see issue
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#459">459</a>), but it doesn't solve the problem raised by this
issue. Whether we use widen or narrow the <tt>num_get</tt> facet
still has no idea which traits class the user wants to use for
the comparison, because only streams, not facets, are passed traits
classes. The standard does not require that two different
traits classes with the same <tt>char_type</tt> must necessarily
have the same behavior.]</i></p>
<p>Informally, one possibility: require that some of the basic
character operations, such as <tt>eq</tt>, <tt>lt</tt>,
and <tt>assign</tt>, must behave the same way for all traits classes
with the same <tt>char_type</tt>. If we accept that limitation on
traits classes, then the facet could reasonably be required to
use <tt>char_traits&lt;charT&gt;</tt></p>.
<hr>
<a name="430"><h3>430.&nbsp;valarray subset operations</h3></a><p><b>Section:</b>&nbsp;26.5.2.4 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.valarray.sub"> [lib.valarray.sub]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;18 Sep 2003</p>
<p>
The standard fails to specify the behavior of valarray::operator[](slice)
and other valarray subset operations when they are passed an "invalid"
slice object, i.e., either a slice that doesn't make sense at all (e.g.,
slice (0, 1, 0) or one that doesn't specify a valid subset of the valarray
object (e.g., slice (2, 1, 1) for a valarray of size 1).
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Kona: the LWG believes that invalid slices should invoke
undefined behavior. Valarrays are supposed to be designed for high
performance, so we don't want to require specific checking. We
need wording to express this decision.]</i></p>
<hr>
<a name="431"><h3>431.&nbsp;Swapping containers with unequal allocators</h3></a><p><b>Section:</b>&nbsp;20.1.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.default.con.req"> [lib.default.con.req]</a>, 25 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-algorithms.html#lib.algorithms"> [lib.algorithms]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;20 Sep 2003</p>
<p>Clause 20.1.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.default.con.req"> [lib.default.con.req]</a> paragraph 4 says that implementations
are permitted to supply containers that are unable to cope with
allocator instances and that container implementations may assume
that all instances of an allocator type compare equal. We gave
implementers this latitude as a temporary hack, and eventually we
want to get rid of it. What happens when we're dealing with
allocators that <i>don't</i> compare equal?
</p>
<p>In particular: suppose that <tt>v1</tt> and <tt>v2</tt> are both
objects of type <tt>vector&lt;int, my_alloc&gt;</tt> and that
<tt>v1.get_allocator() != v2.get_allocator()</tt>. What happens if
we write <tt>v1.swap(v2)</tt>? Informally, three possibilities:</p>
<p>1. This operation is illegal. Perhaps we could say that an
implementation is required to check and to throw an exception, or
perhaps we could say it's undefined behavior.</p>
<p>2. The operation performs a slow swap (i.e. using three
invocations of <tt>operator=</tt>, leaving each allocator with its
original container. This would be an O(N) operation.</p>
<p>3. The operation swaps both the vectors' contents and their
allocators. This would be an O(1) operation. That is:</p>
<blockquote>
<pre> my_alloc a1(...);
my_alloc a2(...);
assert(a1 != a2);
vector&lt;int, my_alloc&gt; v1(a1);
vector&lt;int, my_alloc&gt; v2(a2);
assert(a1 == v1.get_allocator());
assert(a2 == v2.get_allocator());
v1.swap(v2);
assert(a1 == v2.get_allocator());
assert(a2 == v1.get_allocator());
</pre>
</blockquote>
<p><b>Proposed resolution:</b></p>
<p><i>[Kona: This is part of a general problem. We need a paper
saying how to deal with unequal allocators in general.]</i></p>
<p><i>[pre-Sydney: Howard argues for option 3 in n1599.]</i></p>
<hr>
<a name="446"><h3>446.&nbsp;Iterator equality between different containers</h3></a><p><b>Section:</b>&nbsp;24.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iterators.html#lib.iterator.requirements"> [lib.iterator.requirements]</a>, 23.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Andy Koenig&nbsp; <b>Date:</b>&nbsp;16 Dec 2003</p>
<p>
What requirements does the standard place on equality comparisons between
iterators that refer to elements of different containers. For example, if
v1 and v2 are empty vectors, is v1.end() == v2.end() allowed to yield true?
Is it allowed to throw an exception?
</p>
<p>
The standard appears to be silent on both questions.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Sydney: The intention is that comparing two iterators from
different containers is undefined, but it's not clear if we say that,
or even whether it's something we should be saying in clause 23 or in
clause 24. Intuitively we might want to say that equality is defined
only if one iterator is reachable from another, but figuring out how
to say it in any sensible way is a bit tricky: reachability is defined
in terms of equality, so we can't also define equality in terms of
reachability.
]</i></p>
<hr>
<a name="454"><h3>454.&nbsp;basic_filebuf::open should accept wchar_t names</h3></a><p><b>Section:</b>&nbsp;27.8.1.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.filebuf.members"> [lib.filebuf.members]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Bill Plauger&nbsp; <b>Date:</b>&nbsp;30 Jan 2004</p>
<pre> basic_filebuf *basic_filebuf::open(const char *, ios_base::open_mode);
</pre>
<p>should be supplemented with the overload:</p>
<pre> basic_filebuf *basic_filebuf::open(const wchar_t *, ios_base::open_mode);
</pre>
<p>
Depending on the operating system, one of these forms is fundamental and
the other requires an implementation-defined mapping to determine the
actual filename.
</p>
<p><i>[Sydney: Yes, we want to allow wchar_t filenames. Bill will
provide wording.]</i></p>
<p><b>Proposed resolution:</b></p>
<p>Change from:</p>
<blockquote>
<pre>basic_filebuf&lt;charT,traits&gt;* open(
const char* s,
ios_base::openmode mode );
</pre>
<p>
Effects: If is_open() != false, returns a null pointer.
Otherwise, initializes the filebuf as required. It then
opens a file, if possible, whose name is the NTBS s ("as if"
by calling std::fopen(s,modstr)).</p>
</blockquote>
<p>to:</p>
<blockquote>
<pre>basic_filebuf&lt;charT,traits&gt;* open(
const char* s,
ios_base::openmode mode );
basic_filebuf&lt;charT,traits&gt;* open(
const wchar_t* ws,
ios_base::openmode mode );
</pre>
<p>
Effects: If is_open() != false, returns a null pointer.
Otherwise, initializes the filebuf as required. It then
opens a file, if possible, whose name is the NTBS s ("as if"
by calling std::fopen(s,modstr)).
For the second signature, the NTBS s is determined from the
WCBS ws in an implementation-defined manner.
</p>
<p>
(NOTE: For a system that "naturally" represents a filename
as a WCBS, the NTBS s in the first signature may instead
be mapped to a WCBS; if so, it follows the same mapping
rules as the first argument to open.)
</p>
</blockquote>
<p><b>Rationale:</b></p>
<p>
Slightly controversial, but by a 7-1 straw poll the LWG agreed to move
this to Ready. The controversy was because the mapping between wide
names and files in a filesystem is implementation defined. The
counterargument, which most but not all LWG members accepted, is that
the mapping between narrow files names and files is also
implemenation defined.</p>
<p><i>[Lillehammer: Moved back to "open" status, at Beman's urging.
(1) Why just basic_filebuf, instead of also basic_fstream (and
possibly other things too). (2) Why not also constructors that take
std::basic_string? (3) We might want to wait until we see Beman's
filesystem library; we might decide that it obviates this.]</i></p>
<hr>
<a name="456"><h3>456.&nbsp;Traditional C header files are overspecified</h3></a><p><b>Section:</b>&nbsp;17.4.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-intro.html#lib.headers"> [lib.headers]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Bill Plauger&nbsp; <b>Date:</b>&nbsp;30 Jan 2004</p>
<p>The C++ Standard effectively requires that the traditional C headers
(of the form &lt;xxx.h&gt;) be defined in terms of the newer C++
headers (of the form &lt;cxxx&gt;). Clauses 17.4.1.2/4 and D.5 combine
to require that:</p>
<ul>
<li>Including the header &lt;cxxx&gt; declares a C name in namespace std.</li>
<li> Including the header &lt;xxx.h&gt; declares a C name in namespace std
(effectively by including &lt;cxxx&gt;), then imports it into the global
namespace with an individual using declaration.</li>
</ul>
<p>
The rules were left in this form despited repeated and heated objections
from several compiler vendors. The C headers are often beyond the direct
control of C++ implementors. In some organizations, it's all they can do
to get a few #ifdef __cplusplus tests added. Third-party library vendors
can perhaps wrap the C headers. But neither of these approaches supports
the drastic restructuring required by the C++ Standard. As a result, it is
still widespread practice to ignore this conformance requirement, nearly
seven years after the committee last debated this topic. Instead, what is
often implemented is:
</p>
<ul>
<li> Including the header &lt;xxx.h&gt; declares a C name in the
global namespace.</li>
<li> Including the header &lt;cxxx&gt; declares a C name in the
global namespace (effectively by including &lt;xxx.h&gt;), then
imports it into namespace std with an individual using declaration.</li>
</ul>
<p>
The practical benefit for implementors with the second approach is that
they can use existing C library headers, as they are pretty much obliged
to do. The practical cost for programmers facing a mix of implementations
is that they have to assume weaker rules:</p>
<ul>
<li> If you want to assuredly declare a C name in the global
namespace, include &lt;xxx.h&gt;. You may or may not also get the
declaration in namespace std.</li>
<li> If you want to assuredly declare a C name in namespace std,
include &lt;cxxx.h&gt;. You may or may not also get the declaration in
the global namespace.</li>
</ul>
<p>
There also exists the <i>possibility</i> of subtle differences due to
Koenig lookup, but there are so few non-builtin types defined in the C
headers that I've yet to see an example of any real problems in this
area.
</p>
<p>
It is worth observing that the rate at which programmers fall afoul of
these differences has remained small, at least as measured by newsgroup
postings and our own bug reports. (By an overwhelming margin, the
commonest problem is still that programmers include &lt;string&gt; and can't
understand why the typename string isn't defined -- this a decade after
the committee invented namespace std, nominally for the benefit of all
programmers.)
</p>
<p>
We should accept the fact that we made a serious mistake and rectify it,
however belatedly, by explicitly allowing either of the two schemes for
declaring C names in headers.
</p>
<p><i>[Sydney: This issue has been debated many times, and will
certainly have to be discussed in full committee before any action
can be taken. However, the preliminary sentiment of the LWG was in
favor of the change. (6 yes, 0 no, 2 abstain) Robert Klarer
suggests that we might also want to undeprecate the
C-style <tt>.h</tt> headers.]</i></p>
<p><b>Proposed resolution:</b></p>
<hr>
<a name="458"><h3>458.&nbsp;24.1.5 contains unintented limitation for operator-</h3></a><p><b>Section:</b>&nbsp;24.1.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iterators.html#lib.random.access.iterators"> [lib.random.access.iterators]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Daniel Frey&nbsp; <b>Date:</b>&nbsp;27 Feb 2004</p>
<p>
In 24.1.5 [lib.random.access.iterators], table 76 the operational
semantics for the expression "r -= n" are defined as "return r += -n".
This means, that the expression -n must be valid, which is not the case
for unsigned types.
</p>
<p><i>[
Sydney: Possibly not a real problem, since difference type is required
to be a signed integer type. However, the wording in the standard may
be less clear than we would like.
]</i></p>
<p><b>Proposed resolution:</b></p>
<p>
To remove this limitation, I suggest to change the
operational semantics for this column to:
</p>
<code>
{ Distance m = n;
if (m &gt;= 0)
while (m--) --r;
else
while (m++) ++r;
return r; }
</code>
<hr>
<a name="459"><h3>459.&nbsp;Requirement for widening in stage 2 is overspecification</h3></a><p><b>Section:</b>&nbsp;22.2.2.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-locales.html#lib.facet.num.get.virtuals"> [lib.facet.num.get.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;16 Mar 2004</p>
<p>When parsing strings of wide-character digits, the standard
requires the library to widen narrow-character "atoms" and compare
the widened atoms against the characters that are being parsed.
Simply narrowing the wide characters would be far simpler, and
probably more efficient. The two choices are equivalent except in
convoluted test cases, and many implementations already ignore the
standard and use narrow instead of widen.</p>
<p>
First, I disagree that using narrow() instead of widen() would
necessarily have unfortunate performance implications. A possible
implementation of narrow() that allows num_get to be implemented
in a much simpler and arguably comparably efficient way as calling
widen() allows, i.e. without making a virtual call to do_narrow every
time, is as follows:
</p>
<pre> inline char ctype&lt;wchar_t&gt;::narrow (wchar_t wc, char dflt) const
{
const unsigned wi = unsigned (wc);
if (wi &gt; UCHAR_MAX)
return typeid (*this) == typeid (ctype&lt;wchar_t&gt;) ?
dflt : do_narrow (wc, dflt);
if (narrow_ [wi] &lt; 0) {
const char nc = do_narrow (wc, dflt);
if (nc == dflt)
return dflt;
narrow_ [wi] = nc;
}
return char (narrow_ [wi]);
}
</pre>
<p>
Second, I don't think the change proposed in the issue (i.e., to use
narrow() instead of widen() during Stage 2) would be at all
drastic. Existing implementations with the exception of libstdc++
currently already use narrow() so the impact of the change on programs
would presumably be isolated to just a single implementation. Further,
since narrow() is not required to translate alternate wide digit
representations such as those mentioned in issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#303">303</a> to
their narrow equivalents (i.e., the portable source characters '0'
through '9'), the change does not necessarily imply that these
alternate digits would be treated as ordinary digits and accepted as
part of numbers during parsing. In fact, the requirement in 22.2.1.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-locales.html#lib.locale.ctype.virtuals"> [lib.locale.ctype.virtuals]</a>, p13 forbids narrow() to translate an alternate
digit character, wc, to an ordinary digit in the basic source
character set unless the expression
(ctype&lt;charT&gt;::is(ctype_base::digit, wc) == true) holds. This in
turn is prohibited by the C standard (7.25.2.1.5, 7.25.2.1.5, and
5.2.1, respectively) for charT of either char or wchar_t.
</p>
<p><i>[Sydney: To a large extent this is a nonproblem. As long as
you're only trafficking in char and wchar_t we're only dealing with a
stable character set, so you don't really need either 'widen' or
'narrow': can just use literals. Finally, it's not even clear whether
widen-vs-narrow is the right question; arguably we should be using
codecvt instead.]</i></p>
<p><b>Proposed resolution:</b></p>
<p>Change stage 2 so that implementations are permitted to use either
technique to perform the comparison:</p>
<ol>
<li> call widen on the atoms and compare (either by using
operator== or char_traits&lt;charT&gt;::eq) the input with
the widened atoms, or</li>
<li> call narrow on the input and compare the narrow input
with the atoms</li>
<li> do (1) or (2) only if charT is not char or wchar_t,
respectively; i.e., avoid calling widen or narrow
if it the source and destination types are the same</li>
</ol>
<hr>
<a name="462"><h3>462.&nbsp;Destroying objects with static storage duration</h3></a><p><b>Section:</b>&nbsp;3.6.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/basic.html#basic.start.term"> [basic.start.term]</a>, 18.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-support.html#lib.cstdint"> [lib.cstdint]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Bill Plauger&nbsp; <b>Date:</b>&nbsp;23 Mar 2004</p>
<p>
3.6.3 Termination spells out in detail the interleaving of static
destructor calls and calls to functions registered with atexit. To
match this behavior requires intimate cooperation between the code
that calls destructors and the exit/atexit machinery. The former
is tied tightly to the compiler; the latter is a primitive mechanism
inherited from C that traditionally has nothing to do with static
construction and destruction. The benefits of intermixing destructor
calls with atexit handler calls is questionable at best, and <i>very</i>
difficult to get right, particularly when mixing third-party C++
libraries with different third-party C++ compilers and C libraries
supplied by still other parties.
</p>
<p>
I believe the right thing to do is defer all static destruction
until after all atexit handlers are called. This is a change in
behavior, but one that is likely visible only to perverse test
suites. At the very least, we should <i>permit</i> deferred destruction
even if we don't require it.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[If this is to be changed, it should probably be changed by CWG.
At this point, however, the LWG is leaning toward NAD. Implementing
what the standard says is hard work, but it's not impossible and
most vendors went through that pain years ago. Changing this
behavior would be a user-visible change, and would break at least
one real application.]</i></p>
<p>
</p>
<hr>
<a name="463"><h3>463.&nbsp;auto_ptr usability issues</h3></a><p><b>Section:</b>&nbsp;20.4.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.meta.unary"> [lib.meta.unary]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Rani Sharoni&nbsp; <b>Date:</b>&nbsp;7 Dec 2003</p>
<p>
TC1 CWG DR #84 effectively made the template&lt;class Y&gt; operator auto_ptr&lt;Y&gt;()
member of auto_ptr (20.4.5.3/4) obsolete.
</p>
<p>
The sole purpose of this obsolete conversion member is to enable copy
initialization base from r-value derived (or any convertible types like
cv-types) case:
</p>
<pre>#include &lt;memory&gt;
using std::auto_ptr;
struct B {};
struct D : B {};
auto_ptr&lt;D&gt; source();
int sink(auto_ptr&lt;B&gt;);
int x1 = sink( source() ); // #1 EDG - no suitable copy constructor
</pre>
<p>
The excellent analysis of conversion operations that was given in the final
auto_ptr proposal
(http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/1997/N1128.pdf)
explicitly specifies this case analysis (case 4). DR #84 makes the analysis
wrong and actually comes to forbid the loophole that was exploited by the
auto_ptr designers.
</p>
<p>
I didn't encounter any compliant compiler (e.g. EDG, GCC, BCC and VC) that
ever allowed this case. This is probably because it requires 3 user defined
conversions and in fact current compilers conform to DR #84.
</p>
<p>
I was surprised to discover that the obsolete conversion member actually has
negative impact of the copy initialization base from l-value derived
case:</p>
<pre>auto_ptr&lt;D&gt; dp;
int x2 = sink(dp); // #2 EDG - more than one user-defined conversion applies
</pre>
<p>
I'm sure that the original intention was allowing this initialization using
the template&lt;class Y&gt; auto_ptr(auto_ptr&lt;Y&gt;&amp; a) constructor (20.4.5.1/4) but
since in this copy initialization it's merely user defined conversion (UDC)
and the obsolete conversion member is UDC with the same rank (for the early
overloading stage) there is an ambiguity between them.
</p>
<p>
Removing the obsolete member will have impact on code that explicitly
invokes it:
</p>
<pre>int y = sink(source().operator auto_ptr&lt;B&gt;());
</pre>
<p>
IMHO no one ever wrote such awkward code and the reasonable workaround for
#1 is:
</p>
<pre>int y = sink( auto_ptr&lt;B&gt;(source()) );
</pre>
<p>
I was even more surprised to find out that after removing the obsolete
conversion member the initialization was still ill-formed:
int x3 = sink(dp); // #3 EDG - no suitable copy constructor
</p>
<p>
This copy initialization semantically requires copy constructor which means
that both template conversion constructor and the auto_ptr_ref conversion
member (20.4.5.3/3) are required which is what was explicitly forbidden in
DR #84. This is a bit amusing case in which removing ambiguity results with
no candidates.
</p>
<p>
I also found exception safety issue with auto_ptr related to auto_ptr_ref:
</p>
<pre>int f(auto_ptr&lt;B&gt;, std::string);
auto_ptr&lt;B&gt; source2();
// string constructor throws while auto_ptr_ref
// "holds" the pointer
int x4 = f(source2(), "xyz"); // #4
</pre>
<p>
The theoretic execution sequence that will cause a leak:
</p>
<ol>
<li>call auto_ptr&lt;B&gt;::operator auto_ptr_ref&lt;B&gt;()</li>
<li>call string::string(char const*) and throw</li>
</ol>
<p>
According to 20.4.5.3/3 and 20.4.5/2 the auto_ptr_ref conversion member
returns auto_ptr_ref&lt;Y&gt; that holds *this and this is another defect since
the type of *this is auto_ptr&lt;X&gt; where X might be different from Y. Several
library vendors (e.g. SGI) implement auto_ptr_ref&lt;Y&gt; with Y* as member which
is much more reasonable. Other vendor implemented auto_ptr_ref as
defectively required and it results with awkward and catastrophic code:
int oops = sink(auto_ptr&lt;B&gt;(source())); // warning recursive on all control
paths
</p>
<p>
Dave Abrahams noticed that there is no specification saying that
auto_ptr_ref copy constructor can't throw.
</p>
<p>
My proposal comes to solve all the above issues and significantly simplify
auto_ptr implementation. One of the fundamental requirements from auto_ptr
is that it can be constructed in an intuitive manner (i.e. like ordinary
pointers) but with strict ownership semantics which yield that source
auto_ptr in initialization must be non-const. My idea is to add additional
constructor template with sole propose to generate ill-formed, diagnostic
required, instance for const auto_ptr arguments during instantiation of
declaration. This special constructor will not be instantiated for other
types which is achievable using 14.8.2/2 (SFINAE). Having this constructor
in hand makes the constructor template&lt;class Y&gt; auto_ptr(auto_ptr&lt;Y&gt; const&amp;)
legitimate since the actual argument can't be const yet non const r-value
are acceptable.
</p>
<p>
This implementation technique makes the "private auxiliary class"
auto_ptr_ref obsolete and I found out that modern C++ compilers (e.g. EDG,
GCC and VC) consume the new implementation as expected and allow all
intuitive initialization and assignment cases while rejecting illegal cases
that involve const auto_ptr arguments.
</p>
<p>The proposed auto_ptr interface:</p>
<pre>namespace std {
template&lt;class X&gt; class auto_ptr {
public:
typedef X element_type;
// 20.4.5.1 construct/copy/destroy:
explicit auto_ptr(X* p=0) throw();
auto_ptr(auto_ptr&amp;) throw();
template&lt;class Y&gt; auto_ptr(auto_ptr&lt;Y&gt; const&amp;) throw();
auto_ptr&amp; operator=(auto_ptr&amp;) throw();
template&lt;class Y&gt; auto_ptr&amp; operator=(auto_ptr&lt;Y&gt;) throw();
~auto_ptr() throw();
// 20.4.5.2 members:
X&amp; operator*() const throw();
X* operator-&gt;() const throw();
X* get() const throw();
X* release() throw();
void reset(X* p=0) throw();
private:
template&lt;class U&gt;
auto_ptr(U&amp; rhs, typename
unspecified_error_on_const_auto_ptr&lt;U&gt;::type = 0);
};
}
</pre>
<p>
One compliant technique to implement the unspecified_error_on_const_auto_ptr
helper class is using additional private auto_ptr member class template like
the following:
</p>
<pre>template&lt;typename T&gt; struct unspecified_error_on_const_auto_ptr;
template&lt;typename T&gt;
struct unspecified_error_on_const_auto_ptr&lt;auto_ptr&lt;T&gt; const&gt;
{ typedef typename auto_ptr&lt;T&gt;::const_auto_ptr_is_not_allowed type; };
</pre>
<p>
There are other techniques to implement this helper class that might work
better for different compliers (i.e. better diagnostics) and therefore I
suggest defining its semantic behavior without mandating any specific
implementation. IMO, and I didn't found any compiler that thinks otherwise,
14.7.1/5 doesn't theoretically defeat the suggested technique but I suggest
verifying this with core language experts.
</p>
<p><b>Further changes in standard text:</b></p>
<p>Remove section 20.4.5.3</p>
<p>Change 20.4.5/2 to read something like:
Initializing auto_ptr&lt;X&gt; from const auto_ptr&lt;Y&gt; will result with unspecified
ill-formed declaration that will require unspecified diagnostic.</p>
<p>Change 20.4.5.1/4,5,6 to read:</p>
<pre>template&lt;class Y&gt; auto_ptr(auto_ptr&lt;Y&gt; const&amp; a) throw();</pre>
<p> 4 Requires: Y* can be implicitly converted to X*.</p>
<p> 5 Effects: Calls const_cast&lt;auto_ptr&lt;Y&gt;&amp;&gt;(a).release().</p>
<p> 6 Postconditions: *this holds the pointer returned from a.release().</p>
<p>Change 20.4.5.1/10</p>
<pre>template&lt;class Y&gt; auto_ptr&amp; operator=(auto_ptr&lt;Y&gt; a) throw();
</pre>
<p>
10 Requires: Y* can be implicitly converted to X*. The expression delete
get() is well formed.
</p>
<p>LWG TC DR #127 is obsolete.</p>
<p>
Notice that the copy constructor and copy assignment operator should remain
as before and accept non-const auto_ptr&amp; since they have effect on the form
of the implicitly declared copy constructor and copy assignment operator of
class that contains auto_ptr as member per 12.8/5,10:
</p>
<pre>struct X {
// implicit X(X&amp;)
// implicit X&amp; operator=(X&amp;)
auto_ptr&lt;D&gt; aptr_;
};
</pre>
<p>
In most cases this indicates about sloppy programming but preserves the
current auto_ptr behavior.
</p>
<p>
Dave Abrahams encouraged me to suggest fallback implementation in case that
my suggestion that involves removing of auto_ptr_ref will not be accepted.
In this case removing the obsolete conversion member to auto_ptr&lt;Y&gt; and
20.4.5.3/4,5 is still required in order to eliminate ambiguity in legal
cases. The two constructors that I suggested will co exist with the current
members but will make auto_ptr_ref obsolete in initialization contexts.
auto_ptr_ref will be effective in assignment contexts as suggested in DR
#127 and I can't see any serious exception safety issues in those cases
(although it's possible to synthesize such). auto_ptr_ref&lt;X&gt; semantics will
have to be revised to say that it strictly holds pointer of type X and not
reference to an auto_ptr for the favor of cases in which auto_ptr_ref&lt;Y&gt; is
constructed from auto_ptr&lt;X&gt; in which X is different from Y (i.e. assignment
from r-value derived to base).
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Redmond: punt for the moment. We haven't decided yet whether we
want to fix auto_ptr for C++-0x, or remove it and replace it with
move_ptr and unique_ptr.]</i></p>
<hr>
<a name="466"><h3>466.&nbsp;basic_string ctor should prevent null pointer error</h3></a><p><b>Section:</b>&nbsp;21.3.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-strings.html#lib.string.cons"> [lib.string.cons]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Daniel Frey&nbsp; <b>Date:</b>&nbsp;10 Jun 2004</p>
<p>
Today, my colleagues and me wasted a lot of time. After some time, I
found the problem. It could be reduced to the following short example:
</p>
<pre> #include &lt;string&gt;
int main() { std::string( 0 ); }
</pre>
<p>The problem is that the tested compilers (GCC 2.95.2, GCC 3.3.1 and
Comeau online) compile the above without errors or warnings! The
programs (at least for the GCC) resulted in a SEGV.</p>
<p>I know that the standard explicitly states that the ctor of string
requires a char* which is not zero. STLs could easily detect the above
case with a private ctor for basic_string which takes a single 'int'
argument. This would catch the above code at compile time and would not
ambiguate any other legal ctors.</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Redmond: No great enthusiasm for doing this. If we do,
however, we want to do it for all places that take <tt>charT*</tt>
pointers, not just the single-argument constructor. The other
question is whether we want to catch this at compile time (in which
case we catch the error of a literal 0, but not an expression whose
value is a null pointer), at run time, or both.]</i></p>
<hr>
<a name="470"><h3>470.&nbsp;accessing containers from their elements' special functions</h3></a><p><b>Section:</b>&nbsp;23 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.containers"> [lib.containers]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;28 Jun 2004</p>
<p>
The standard doesn't prohibit the destructors (or any other special
functions) of containers' elements invoked from a member function
of the container from "recursively" calling the same (or any other)
member function on the same container object, potentially while the
container is in an intermediate state, or even changing the state
of the container object while it is being modified. This may result
in some surprising (i.e., undefined) behavior.
</p>
<p>Read email thread starting with c++std-lib-13637 for more.</p>
<p><b>Proposed resolution:</b></p>
<p>Add to Container Requirements the following new paragraph:</p>
<pre> Unless otherwise specified, the behavior of a program that
invokes a container member function f from a member function
g of the container's value_type on a container object c that
called g from its mutating member function h, is undefined.
I.e., if v is an element of c, directly or indirectly calling
c.h() from v.g() called from c.f(), is undefined.
</pre>
<p><i>[Redmond: This is a real issue, but it's probably a clause 17
issue, not clause 23. We get the same issue, for example, if we
try to destroy a stream from one of the stream's callback functions.]</i></p>
<hr>
<a name="471"><h3>471.&nbsp;result of what() implementation-defined</h3></a><p><b>Section:</b>&nbsp;18.6.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-support.html#lib.type.info"> [lib.type.info]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;28 Jun 2004</p>
<p>[lib.exception] specifies the following:</p>
<pre> exception (const exception&amp;) throw();
exception&amp; operator= (const exception&amp;) throw();
-4- Effects: Copies an exception object.
-5- Notes: The effects of calling what() after assignment
are implementation-defined.
</pre>
<p>
First, does the Note only apply to the assignment operator? If so,
what are the effects of calling what() on a copy of an object? Is
the returned pointer supposed to point to an identical copy of
the NTBS returned by what() called on the original object or not?
</p>
<p>
Second, is this Note intended to extend to all the derived classes
in section 19? I.e., does the standard provide any guarantee for
the effects of what() called on a copy of any of the derived class
described in section 19?
</p>
<p>
Finally, if the answer to the first question is no, I believe it
constitutes a defect since throwing an exception object typically
implies invoking the copy ctor on the object. If the answer is yes,
then I believe the standard ought to be clarified to spell out
exactly what the effects are on the copy (i.e., after the copy
ctor was called).
</p>
<p><i>[Redmond: Yes, this is fuzzy. The issue of derived classes is
fuzzy too.]</i></p>
<p><b>Proposed resolution:</b></p>
<hr>
<a name="473"><h3>473.&nbsp;underspecified ctype calls</h3></a><p><b>Section:</b>&nbsp;22.2.1.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-locales.html#lib.locale.ctype"> [lib.locale.ctype]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;1 Jul 2004</p>
<p>
Most ctype member functions come in two forms: one that operates
on a single character at a time and another form that operates
on a range of characters. Both forms are typically described by
a single Effects and/or Returns clause.
</p>
<p>
The Returns clause of each of the single-character non-virtual forms
suggests that the function calls the corresponding single character
virtual function, and that the array form calls the corresponding
virtual array form. Neither of the two forms of each virtual member
function is required to be implemented in terms of the other.
</p>
<p>
There are three problems:
</p>
<p>
1. One is that while the standard does suggest that each non-virtual
member function calls the corresponding form of the virtual function,
it doesn't actually explicitly require it.
</p>
<p>
Implementations that cache results from some of the virtual member
functions for some or all values of their arguments might want to
call the array form from the non-array form the first time to fill
the cache and avoid any or most subsequent virtual calls. Programs
that rely on each form of the virtual function being called from
the corresponding non-virtual function will see unexpected behavior
when using such implementations.
</p>
<p>
2. The second problem is that either form of each of the virtual
functions can be overridden by a user-defined function in a derived
class to return a value that is different from the one produced by
the virtual function of the alternate form that has not been
overriden.
</p>
<p>
Thus, it might be possible for, say, ctype::widen(c) to return one
value, while for ctype::widen(&amp;c, &amp;c + 1, &amp;wc) to set
wc to another value. This is almost certainly not intended. Both
forms of every function should be required to return the same result
for the same character, otherwise the same program using an
implementation that calls one form of the functions will behave
differently than when using another implementation that calls the
other form of the function "under the hood."
</p>
<p>
3. The last problem is that the standard text fails to specify whether
one form of any of the virtual functions is permitted to be implemented
in terms of the other form or not, and if so, whether it is required
or permitted to call the overridden virtual function or not.
</p>
<p>
Thus, a program that overrides one of the virtual functions so that
it calls the other form which then calls the base member might end
up in an infinite loop if the called form of the base implementation
of the function in turn calls the other form.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Lillehammer: Part of this isn't a real problem. We already talk about
caching. 22.1.1/6 But part is a real problem. ctype virtuals may call
each other, so users don't know which ones to override to avoid avoid
infinite loops.</p>
<p>This is a problem for all facet virtuals, not just ctype virtuals,
so we probably want a blanket statement in clause 22 for all
facets. The LWG is leaning toward a blanket prohibition, that a
facet's virtuals may never call each other. We might want to do that
in clause 27 too, for that matter. A review is necessary. Bill will
provide wording.</p>
<hr>
<a name="479"><h3>479.&nbsp;Container requirements and placement new</h3></a><p><b>Section:</b>&nbsp;23.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Herb Sutter&nbsp; <b>Date:</b>&nbsp;1 Aug 2004</p>
<p>Nothing in the standard appears to make this program ill-formed:</p>
<pre> struct C {
void* operator new( size_t s ) { return ::operator new( s ); }
// NOTE: this hides in-place and nothrow new
};
int main() {
vector&lt;C&gt; v;
v.push_back( C() );
}
</pre>
<p>Is that intentional? We should clarify whether or not we intended
to require containers to support types that define their own special
versions of <tt>operator new</tt>.</p>
<p><i>[
Lillehammer: A container will definitely never use this overridden
operator new, but whether it will fail to compile is unclear from the
standard. Are containers supposed to use qualified or unqualified
placement new? 20.4.1.1 is somewhat relevant, but the standard
doesn't make it completely clear whether containers have to use
Allocator::construct(). If containers don't use it, the details of how
containers use placement new are unspecified. That is the real bug,
but it needs to be fixed as part of the allocator overhaul. Weak
support that the eventual solution should make this code well formed.
]</i></p>
<p><b>Proposed resolution:</b></p>
<hr>
<a name="482"><h3>482.&nbsp;Swapping pairs</h3></a><p><b>Section:</b>&nbsp;20.2.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.pairs"> [lib.pairs]</a>, 25.2.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-algorithms.html#lib.alg.swap"> [lib.alg.swap]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Andrew Koenig&nbsp; <b>Date:</b>&nbsp;14 Sep 2004</p>
<p>(Based on recent comp.std.c++ discussion)</p>
<p>Pair (and tuple) should specialize std::swap to work in terms of
std::swap on their components. For example, there's no obvious reason
why swapping two objects of type pair&lt;vector&lt;int&gt;,
list&lt;double&gt; &gt; should not take O(1).</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Lillehammer: We agree it should be swappable. Howard will
provide wording.]</i></p>
<hr>
<a name="484"><h3>484.&nbsp;Convertible to T</h3></a><p><b>Section:</b>&nbsp;24.1.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iterators.html#lib.input.iterators"> [lib.input.iterators]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Chris Jefferson&nbsp; <b>Date:</b>&nbsp;16 Sep 2004</p>
<p>From comp.std.c++:</p>
<p>
I note that given an input iterator a for type T,
then *a only has to be "convertable to T", not actually of type T.
</p>
<p>Firstly, I can't seem to find an exact definition of "convertable to T".
While I assume it is the obvious definition (an implicit conversion), I
can't find an exact definition. Is there one?</p>
<p>Slightly more worryingly, there doesn't seem to be any restriction on
the this type, other than it is "convertable to T". Consider two input
iterators a and b. I would personally assume that most people would
expect *a==*b would perform T(*a)==T(*b), however it doesn't seem that
the standard requires that, and that whatever type *a is (call it U)
could have == defined on it with totally different symantics and still
be a valid inputer iterator.</p>
<p>Is this a correct reading? When using input iterators should I write
T(*a) all over the place to be sure that the object i'm using is the
class I expect?</p>
<p>This is especially a nuisance for operations that are defined to be
"convertible to bool". (This is probably allowed so that
implementations could return say an int and avoid an unnessary
conversion. However all implementations I have seen simply return a
bool anyway. Typical implemtations of STL algorithms just write
things like <tt>while(a!=b &amp;&amp; *a!=0)</tt>. But strictly
speaking, there are lots of types that are convertible to T but
that also overload the appropriate operators so this doesn't behave
as expected.</p>
<p>If we want to make code like this legal (which most people seem to
expect), then we'll need to tighten up what we mean by "convertible
to T".</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Lillehammer: The first part is NAD, since "convertible" is
well-defined in core. The second part is basically about pathological
overloads. It's a minor problem but a real one. So leave open for
now, hope we solve it as part of iterator redesign.]</i></p>
<hr>
<a name="485"><h3>485.&nbsp;output iterator insufficently constrained</h3></a><p><b>Section:</b>&nbsp;24.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iterators.html#lib.output.iterators"> [lib.output.iterators]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Chris Jefferson&nbsp; <b>Date:</b>&nbsp;13 Oct 2004</p>
<p>
The note on 24.1.2 Output iterators insufficently limits what can be
performed on output iterators. While it requires that each iterator is
progressed through only once and that each iterator is written to only
once, it does not require the following things:</p>
<p>Note: Here it is assumed that x is an output iterator of type X which
has not yet been assigned to.</p>
<p>a) That each value of the output iterator is written to:
The standard allows:
++x; ++x; ++x;
</p>
<p>
b) That assignments to the output iterator are made in order
X a(x); ++a; *a=1; *x=2; is allowed
</p>
<p>
c) Chains of output iterators cannot be constructed:
X a(x); ++a; X b(a); ++b; X c(b); ++c; is allowed, and under the current
wording (I believe) x,a,b,c could be written to in any order.
</p>
<p>I do not believe this was the intension of the standard?</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Lillehammer: Real issue. There are lots of constraints we
intended but didn't specify. Should be solved as part of iterator
redesign.]</i></p>
<hr>
<a name="488"><h3>488.&nbsp;rotate throws away useful information</h3></a><p><b>Section:</b>&nbsp;25.2.10 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-algorithms.html#lib.alg.rotate"> [lib.alg.rotate]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Howard Hinnant&nbsp; <b>Date:</b>&nbsp;22 Nov 2004</p>
<p>
rotate takes 3 iterators: first, middle and last which point into a
sequence, and rearranges the sequence such that the subrange [middle,
last) is now at the beginning of the sequence and the subrange [first,
middle) follows. The return type is void.
</p>
<p>
In many use cases of rotate, the client needs to know where the
subrange [first, middle) starts after the rotate is performed. This
might look like:
</p>
<pre> rotate(first, middle, last);
Iterator i = advance(first, distance(middle, last));
</pre>
<p>
Unless the iterators are random access, the computation to find the
start of the subrange [first, middle) has linear complexity. However,
it is not difficult for rotate to return this information with
negligible additional computation expense. So the client could code:
</p>
<pre> Iterator i = rotate(first, middle, last);
</pre>
<p>
and the resulting program becomes significantly more efficient.
</p>
<p>
While the backwards compatibility hit with this change is not zero, it
is very small (similar to that of lwg <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#130">130</a>), and there is
a significant benefit to the change.
</p>
<p><b>Proposed resolution:</b></p>
<p>In 25p2, change:</p>
<pre> template&lt;class ForwardIterator&gt;
void rotate(ForwardIterator first, ForwardIterator middle,
ForwardIterator last);
</pre>
<p>to:</p>
<pre> template&lt;class ForwardIterator&gt;
ForwardIterator rotate(ForwardIterator first, ForwardIterator middle,
ForwardIterator last);
</pre>
<p>In 25.2.10, change:</p>
<pre> template&lt;class ForwardIterator&gt;
void rotate(ForwardIterator first, ForwardIterator middle,
ForwardIterator last);
</pre>
<p>to:</p>
<pre> template&lt;class ForwardIterator&gt;
ForwardIterator rotate(ForwardIterator first, ForwardIterator middle,
ForwardIterator last);
</pre>
<p>In 25.2.10 insert a new paragraph after p1:</p>
<blockquote>
<p><b>Returns</b>: <tt>first + (last - middle)</tt>.</p>
</blockquote>
<p><i>[
The LWG agrees with this idea, but has one quibble: we want to make
sure not to give the impression that the function "advance" is
actually called, just that the nth iterator is returned. (Calling
advance is observable behavior, since users can specialize it for
their own iterators.) Howard will provide wording.
]</i></p>
<p><i>[Howard provided wording for mid-meeting-mailing Jun. 2005.]</i></p>
<hr>
<a name="492"><h3>492.&nbsp;Invalid iterator arithmetic expressions</h3></a><p><b>Section:</b>&nbsp;23 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.containers"> [lib.containers]</a>, 24 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iterators.html#lib.iterators"> [lib.iterators]</a>, 25 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-algorithms.html#lib.algorithms"> [lib.algorithms]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Thomas Mang&nbsp; <b>Date:</b>&nbsp;12 Dec 2004</p>
<p>Various clauses other than clause 25 make use of iterator arithmetic not
supported by the iterator category in question.
Algorithms in clause 25 are exceptional because of 25 [lib.algorithms],
paragraph 9, but this paragraph does not provide semantics to the
expression "iterator - n", where n denotes a value of a distance type
between iterators.</p>
<p>1) Examples of current wording:</p>
<p>Current wording outside clause 25:</p>
<p>
23.2.2.4 [lib.list.ops], paragraphs 19-21: "first + 1", "(i - 1)",
"(last - first)"
23.3.1.1 [lib.map.cons], paragraph 4: "last - first"
23.3.2.1 [lib.multimap.cons], paragraph 4: "last - first"
23.3.3.1 [lib.set.cons], paragraph 4: "last - first"
23.3.4.1 [lib.multiset.cons], paragraph 4: "last - first"
24.4.1 [lib.reverse.iterators], paragraph 1: "(i - 1)"
</p>
<p>
[Important note: The list is not complete, just an illustration. The
same issue might well apply to other paragraphs not listed here.]</p>
<p>None of these expressions is valid for the corresponding iterator
category.</p>
<p>Current wording in clause 25:</p>
<p>
25.1.1 [lib.alg.foreach], paragraph 1: "last - 1"
25.1.3 [lib.alg.find.end], paragraph 2: "[first1, last1 -
(last2-first2))"
25.2.8 [lib.alg.unique], paragraph 1: "(i - 1)"
25.2.8 [lib.alg.unique], paragraph 5: "(i - 1)"
</p>
<p>
However, current wording of 25 [lib.algorithms], paragraph 9 covers
neither of these four cases:</p>
<p>Current wording of 25 [lib.algorithms], paragraph 9:</p>
<p>
"In the description of the algorithms operator + and - are used for some
of the iterator categories for which they do not have to be defined. In
these cases the semantics of a+n is the same as that of</p>
<pre>{X tmp = a;
advance(tmp, n);
return tmp;
}
</pre>
<p>and that of b-a is the same as of return distance(a, b)"</p>
<p>
This paragrpah does not take the expression "iterator - n" into account,
where n denotes a value of a distance type between two iterators [Note:
According to current wording, the expression "iterator - n" would be
resolved as equivalent to "return distance(n, iterator)"]. Even if the
expression "iterator - n" were to be reinterpreted as equivalent to
"iterator + -n" [Note: This would imply that "a" and "b" were
interpreted implicitly as values of iterator types, and "n" as value of
a distance type], then 24.3.4/2 interfers because it says: "Requires: n
may be negative only for random access and bidirectional iterators.",
and none of the paragraphs quoted above requires the iterators on which
the algorithms operate to be of random access or bidirectional category.
</p>
<p>2) Description of intended behavior:</p>
<p>
For the rest of this Defect Report, it is assumed that the expression
"iterator1 + n" and "iterator1 - iterator2" has the semantics as
described in current 25 [lib.algorithms], paragraph 9, but applying to
all clauses. The expression "iterator1 - n" is equivalent to an
result-iterator for which the expression "result-iterator + n" yields an
iterator denoting the same position as iterator1 does. The terms
"iterator1", "iterator2" and "result-iterator" shall denote the value of
an iterator type, and the term "n" shall denote a value of a distance
type between two iterators.</p>
<p>
All implementations known to the author of this Defect Report comply
with these assumptions.
No impact on current code is expected.</p>
<p>3) Proposed fixes:</p>
<p>Change 25 [lib.algorithms], paragraph 9 to:</p>
<p>
"In the description of the algorithms operator + and - are used for some
of the iterator categories for which they do not have to be defined. In
this paragraph, a and b denote values of an iterator type, and n denotes
a value of a distance type between two iterators. In these cases the
semantics of a+n is the same as that of</p>
<pre>{X tmp = a;
advance(tmp, n);
return tmp;
}
</pre>
<p>,the semantics of a-n denotes the value of an iterator i for which the
following condition holds:
advance(i, n) == a,
and that of b-a is the same as of
return distance(a, b)".
</p>
<p>Comments to the new wording:</p>
<p>
a) The wording " In this paragraph, a and b denote values of an iterator
type, and n denotes a value of a distance type between two iterators."
was added so the expressions "b-a" and "a-n" are distinguished regarding
the types of the values on which they operate.
b) The wording ",the semantics of a-n denotes the value of an iterator i
for which the following condition holds: advance(i, n) == a" was added
to cover the expression 'iterator - n'. The wording "advance(i, n) == a"
was used to avoid a dependency on the semantics of a+n, as the wording
"i + n == a" would have implied. However, such a dependency might well
be deserved.
c) DR 225 is not considered in the new wording.
</p>
<p>
Proposed fixes regarding invalid iterator arithmetic expressions outside
clause 25:</p>
<p>
Either
a) Move modified 25 [lib.algorithms], paragraph 9 (as proposed above)
before any current invalid iterator arithmetic expression. In that case,
the first sentence of 25 [lib.algorithms], paragraph 9, need also to be
modified and could read: "For the rest of this International Standard,
...." / "In the description of the following clauses including this
...." / "In the description of the text below ..." etc. - anyways
substituting the wording "algorithms", which is a straight reference to
clause 25.
In that case, 25 [lib.algorithms] paragraph 9 will certainly become
obsolete.
Alternatively,
b) Add an appropiate paragraph similar to resolved 25 [lib.algorithms],
paragraph 9, to the beginning of each clause containing invalid iterator
arithmetic expressions.
Alternatively,
c) Fix each paragraph (both current wording and possible resolutions of
DRs) containing invalid iterator arithmetic expressions separately.
</p>
<p>5) References to other DRs:</p>
<p>
See DR 225.
See DR 237. The resolution could then also read "Linear in last -
first".
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[Lillehammer: Minor issue, but real. We have a blanket statement
about this in 25/11. But (a) it should be in 17, not 25; and (b) it's
not quite broad enough, because there are some arithmetic expressions
it doesn't cover. Bill will provide wording.]</i></p>
<hr>
<a name="498"><h3>498.&nbsp;Requirements for partition() and stable_partition() too strong</h3></a><p><b>Section:</b>&nbsp;25.2.12 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-algorithms.html#lib.alg.partitions"> [lib.alg.partitions]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Sean Parent, Joe Gottman&nbsp; <b>Date:</b>&nbsp;4 May 2005</p>
<p>
Problem:
The iterator requirements for partition() and stable_partition() [25.2.12]
are listed as BidirectionalIterator, however, there are efficient algorithms
for these functions that only require ForwardIterator that have been known
since before the standard existed. The SGI implementation includes these (see
<a href="http://www.sgi.com/tech/stl/partition.html">http://www.sgi.com/tech/stl/partition.html</a>
and
<a href="http://www.sgi.com/tech/stl/stable_partition.html">http://www.sgi.com/tech/stl/stable_partition.html</a>).
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change 25.2.12 from </p>
<blockquote><pre>template&lt;class BidirectionalIterator, class Predicate&gt;
BidirectionalIterator partition(BidirectionalIterato r first,
BidirectionalIterator last,
Predicate pred);
</pre></blockquote>
<p>to </p>
<blockquote><pre>template&lt;class ForwardIterator, class Predicate&gt;
ForwardIterator partition(ForwardIterator first,
ForwardIterator last,
Predicate pred);
</pre></blockquote>
<p>Change the complexity from </p>
<blockquote><p>
At most (last - first)/2 swaps are done. Exactly (last - first)
applications of the predicate are done.
</p></blockquote>
<p>to </p>
<blockquote><p>
If ForwardIterator is a bidirectional_iterator, at most (last - first)/2
swaps are done; otherwise at most (last - first) swaps are done. Exactly
(last - first) applications of the predicate are done.
</p></blockquote>
<p><b>Rationale:</b></p>
Partition is a "foundation" algorithm useful in many contexts (like sorting
as just one example) - my motivation for extending it to include forward
iterators is slist - without this extension you can't partition an slist
(without writing your own partition). Holes like this in the standard
library weaken the argument for generic programming (ideally I'd be able
to provide a library that would refine std::partition() to other concepts
without fear of conflicting with other libraries doing the same - but
that is a digression). I consider the fact that partition isn't defined
to work for ForwardIterator a minor embarrassment.
<p><i>[Mont Tremblant: Moved to Open, request motivation and use cases
by next meeting. Sean provided further rationale by post-meeting
mailing.]</i></p>
<hr>
<a name="502"><h3>502.&nbsp;Proposition: Clarification of the interaction between a facet and an iterator</h3></a><p><b>Section:</b>&nbsp;22.1.1.1.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-locales.html#lib.locale.category"> [lib.locale.category]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Christopher Conrade Zseleghovski&nbsp; <b>Date:</b>&nbsp;7 Jun 2005</p>
<p>
Motivation:
</p>
<p>
This requirement seems obvious to me, it is the essence of code modularity.
I have complained to Mr. Plauger that the Dinkumware library does not
observe this principle but he objected that this behaviour is not covered in
the standard.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Append the following point to 22.1.1.1.1:
</p>
<p>
6. The implementation of a facet of Table 52 parametrized with an
InputIterator/OutputIterator should use that iterator only as character
source/sink respectively.
For a *_get facet, it means that the value received depends only on the
sequence of input characters and not on how they are accessed.
For a *_put facet, it means that the sequence of characters output depends
only on the value to be formatted and not of how the characters are stored.
</p>
<p><i>[
Berlin: Moved to Open, Need to clean up this area to make it clear
locales don't have to contain open ended sets of facets. Jack, Howard,
Bill.
]</i></p>
<hr>
<a name="503"><h3>503.&nbsp;more on locales</h3></a><p><b>Section:</b>&nbsp;22.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-locales.html#lib.locale.categories"> [lib.locale.categories]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;P.J. Plauger&nbsp; <b>Date:</b>&nbsp;20 Jun 2005</p>
<p>
a) In 22.2.1.1 para. 2 we refer to "the instantiations required in Table
51" to refer to the facet *objects* associated with a locale. And we
almost certainly mean just those associated with the default or "C"
locale. Otherwise, you can't switch to a locale that enforces a different
mapping between narrow and wide characters, or that defines additional
uppercase characters.
</p>
<p>
b) 22.2.1.5 para. 3 (codecvt) has the same issues.
</p>
<p>
c) 22.2.1.5.2 (do_unshift) is even worse. It *forbids* the generation of
a homing sequence for the basic character set, which might very well need
one.
</p>
<p>
d) 22.2.1.5.2 (do_length) likewise dictates that the default mapping
between wide and narrow characters be taken as one-for-one.
</p>
<p>
e) 22.2.2 para. 2 (num_get/put) is both muddled and vacuous, as far as
I can tell. The muddle is, as before, calling Table 51 a list of
instantiations. But the constraint it applies seems to me to cover
*all* defined uses of num_get/put, so why bother to say so?
</p>
<p>
f) 22.2.3.1.2 para. 1(do_decimal_point) says "The required instantiations
return '.' or L'.'.) Presumably this means "as appropriate for the
character type. But given the vague definition of "required" earlier,
this overrules *any* change of decimal point for non "C" locales.
Surely we don't want to do that.
</p>
<p>
g) 22.2.3.1.2 para. 2 (do_thousands_sep) says "The required instantiations
return ',' or L','.) As above, this probably means "as appropriate for the
character type. But this overrules the "C" locale, which requires *no*
character ('\0') for the thousands separator. Even if we agree that we
don't mean to block changes in decimal point or thousands separator,
we should also eliminate this clear incompatibility with C.
</p>
<p>
h) 22.2.3.1.2 para. 2 (do_grouping) says "The required instantiations
return the empty string, indicating no grouping." Same considerations
as for do_decimal_point.
</p>
<p>
i) 22.2.4.1 para. 1 (collate) refers to "instantiations required in Table
51". Same bad jargon.
</p>
<p>
j) 22.2.4.1.2 para. 1 (do_compare) refers to "instantiations required
in Table 51". Same bad jargon.
</p>
<p>
k) 22.2.5 para. 1 (time_get/put) uses the same muddled and vacuous
as num_get/put.
</p>
<p>
l) 22.2.6 para. 2 (money_get/put) uses the same muddled and vacuous
as num_get/put.
</p>
<p>
m) 22.2.6.3.2 (do_pos/neg_format) says "The instantiations required
in Table 51 ... return an object of type pattern initialized to
{symbol, sign, none, value}." This once again *overrides* the "C"
locale, as well as any other locale."
</p>
<p>
3) We constrain the use_facet calls that can be made by num_get/put,
so why don't we do the same for money_get/put? Or for any of the
other facets, for that matter?
</p>
<p>
4) As an almost aside, we spell out when a facet needs to use the ctype
facet, but several also need to use a codecvt facet and we don't say so.
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<p><i>[
Berlin: Bill to provide wording.
]</i></p>
<hr>
<a name="515"><h3>515.&nbsp;Random number engine traits</h3></a><p><b>Section:</b>&nbsp;TR1 5.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.rand.synopsis"> [tr.rand.synopsis]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Walter Brown&nbsp; <b>Date:</b>&nbsp;3 Jul 2005</p>
<p>
To accompany the concept of a pseudo-random number engine as defined in Table 17,
we propose and recommend an adjunct template, engine_traits, to be declared in
[tr.rand.synopsis] as:
</p>
<blockquote><pre>template&lt; class PSRE &gt;
class engine_traits;
</pre></blockquote>
<p>
This template<74>s primary purpose would be as an aid to generic programming involving
pseudo-random number engines. Given only the facilities described in tr1, it would
be very difficult to produce any algorithms involving the notion of a generic engine.
The intent of this proposal is to provide, via engine_traits&lt;&gt;, sufficient
descriptive information to allow an algorithm to employ a pseudo-random number engine
without regard to its exact type, i.e., as a template parameter.
</p>
<p>
For example, today it is not possible to write an efficient generic function that
requires any specific number of random bits. More specifically, consider a
cryptographic application that internally needs 256 bits of randomness per call:
</p>
<blockquote><pre>template&lt; class Eng, class InIter, class OutIter &gt;
void crypto( Eng&amp; e, InIter in, OutIter out );
</pre></blockquote>
<p>
Without knowning the number of bits of randomness produced per call to a provided
engine, the algorithm has no means of determining how many times to call the engine.
</p>
<p>
In a new section [tr.rand.eng.traits], we proposed to define the engine_traits
template as:
</p>
<blockquote><pre>template&lt; class PSRE &gt;
class engine_traits
{
static std::size_t bits_of_randomness = 0u;
static std::string name() { return "unknown_engine"; }
// TODO: other traits here
};
</pre></blockquote>
<p>
Further, each engine described in [tr.rand.engine] would be accompanied by a
complete specialization of this new engine_traits template.
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<p><i>[
Berlin: Walter: While useful for implementation per TR1, N1932 has no need for this
feature.
]</i></p>
<hr>
<a name="518"><h3>518.&nbsp;Are insert and erase stable for unordered_multiset and unordered_multimap?</h3></a><p><b>Section:</b>&nbsp;TR1 6.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.hash"> [tr.hash]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;3 Jul 2005</p>
<p>
Issue 371 deals with stability of multiset/multimap under insert and erase
(i.e. do they preserve the relative order in ranges of equal elements).
The same issue applies to unordered_multiset and unordered_multimap.
</p>
<p><b>Proposed resolution:</b></p>
<p><i>[
Moved to open (from review): There is no resolution.
]</i></p>
<p>
</p>
<hr>
<a name="522"><h3>522.&nbsp;Tuple doesn't define swap</h3></a><p><b>Section:</b>&nbsp;TR1 6.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.tuple"> [tr.tuple]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Andy Koenig&nbsp; <b>Date:</b>&nbsp;3 Jul 2005</p>
<p>
Tuple doesn't define swap(). It should.
</p>
<p><i>[
Berlin: Doug to provide wording.
]</i></p>
<p><b>Proposed resolution:</b></p>
<hr>
<a name="523"><h3>523.&nbsp;regex case-insensitive character ranges are unimplementable as specified</h3></a><p><b>Section:</b>&nbsp;TR1 7 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.re"> [tr.re]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Eric Niebler&nbsp; <b>Date:</b>&nbsp;1 Jul 2005</p>
<p>
A problem with TR1 regex is currently being discussed on the Boost
developers list. It involves the handling of case-insensitive matching
of character ranges such as [Z-a]. The proper behavior (according to the
ECMAScript standard) is unimplementable given the current specification
of the TR1 regex_traits&lt;&gt; class template. John Maddock, the author of
the TR1 regex proposal, agrees there is a problem. The full discussion
can be found at http://lists.boost.org/boost/2005/06/28850.php (first
message copied below). We don't have any recommendations as yet.
</p>
<p>
-- Begin original message --
</p>
<p>
The situation of interest is described in the ECMAScript specification
(ECMA-262), section 15.10.2.15:
</p>
<p>
"Even if the pattern ignores case, the case of the two ends of a range
is significant in determining which characters belong to the range.
Thus, for example, the pattern /[E-F]/i matches only the letters E, F,
e, and f, while the pattern /[E-f]/i matches all upper and lower-case
ASCII letters as well as the symbols [, \, ], ^, _, and `."
</p>
<p>
A more interesting case is what should happen when doing a
case-insentitive match on a range such as [Z-a]. It should match z, Z,
a, A and the symbols [, \, ], ^, _, and `. This is not what happens with
Boost.Regex (it throws an exception from the regex constructor).
</p>
<p>
The tough pill to swallow is that, given the specification in TR1, I
don't think there is any effective way to handle this situation.
According to the spec, case-insensitivity is handled with
regex_traits&lt;&gt;::translate_nocase(CharT) -- two characters are equivalent
if they compare equal after both are sent through the translate_nocase
function. But I don't see any way of using this translation function to
make character ranges case-insensitive. Consider the difficulty of
detecting whether "z" is in the range [Z-a]. Applying the transformation
to "z" has no effect (it is essentially std::tolower). And we're not
allowed to apply the transformation to the ends of the range, because as
ECMA-262 says, "the case of the two ends of a range is significant."
</p>
<p>
So AFAICT, TR1 regex is just broken, as is Boost.Regex. One possible fix
is to redefine translate_nocase to return a string_type containing all
the characters that should compare equal to the specified character. But
this function is hard to implement for Unicode, and it doesn't play nice
with the existing ctype facet. What a mess!
</p>
<p>
-- End original message --
</p>
<p><i>[
John Maddock adds:
]</i></p>
<p>
One small correction, I have since found that ICU's regex package does
implement this correctly, using a similar mechanism to the current
TR1.Regex.
</p>
<p>
Given an expression [c1-c2] that is compiled as case insensitive it:
</p>
<p>
Enumerates every character in the range c1 to c2 and converts it to it's
case folded equivalent. That case folded character is then used a key to a
table of equivalence classes, and each member of the class is added to the
list of possible matches supported by the character-class. This second step
isn't possible with our current traits class design, but isn't necessary if
the input text is also converted to a case-folded equivalent on the fly.
</p>
<p>
ICU applies similar brute force mechanisms to character classes such as
[[:lower:]] and [[:word:]], however these are at least cached, so the impact
is less noticeable in this case.
</p>
<p>
Quick and dirty performance comparisons show that expressions such as
"[X-\\x{fff0}]+" are indeed very slow to compile with ICU (about 200 times
slower than a "normal" expression). For an application that uses a lot of
regexes this could have a noticeable performance impact. ICU also has an
advantage in that it knows the range of valid characters codes: code points
outside that range are assumed not to require enumeration, as they can not
be part of any equivalence class. I presume that if we want the TR1.Regex
to work with arbitrarily large character sets enumeration really does become
impractical.
</p>
<p>
Finally note that Unicode has:
</p>
<p>
Three cases (upper, lower and title).
One to many, and many to one case transformations.
Character that have context sensitive case translations - for example an
uppercase sigma has two different lowercase forms - the form chosen depends
on context(is it end of a word or not), a caseless match for an upper case
sigma should match either of the lower case forms, which is why case folding
is often approximated by tolower(toupper(c)).
</p>
<p>
Probably we need some way to enumerate character equivalence classes,
including digraphs (either as a result or an input), and some way to tell
whether the next character pair is a valid digraph in the current locale.
</p>
<p>
Hoping this doesn't make this even more complex that it was already,
</p>
<p><i>[
Portland: Alisdair: Detect as invalid, throw an exception.
Pete: Possible general problem with case insensitive ranges.
]</i></p>
<p><b>Proposed resolution:</b></p>
<hr>
<a name="524"><h3>524.&nbsp;regex named character classes and case-insensitivity don't mix</h3></a><p><b>Section:</b>&nbsp;TR1 7 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.re"> [tr.re]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Eric Niebler&nbsp; <b>Date:</b>&nbsp;1 Jul 2005</p>
<p>
This defect is also being discussed on the Boost developers list. The
full discussion can be found here:
http://lists.boost.org/boost/2005/07/29546.php
</p>
<p>
-- Begin original message --
</p>
<p>
Also, I may have found another issue, closely related to the one under
discussion. It regards case-insensitive matching of named character
classes. The regex_traits&lt;&gt; provides two functions for working with
named char classes: lookup_classname and isctype. To match a char class
such as [[:alpha:]], you pass "alpha" to lookup_classname and get a
bitmask. Later, you pass a char and the bitmask to isctype and get a
bool yes/no answer.
</p>
<p>
But how does case-insensitivity work in this scenario? Suppose we're
doing a case-insensitive match on [[:lower:]]. It should behave as if it
were [[:lower:][:upper:]], right? But there doesn't seem to be enough
smarts in the regex_traits interface to do this.
</p>
<p>
Imagine I write a traits class which recognizes [[:fubar:]], and the
"fubar" char class happens to be case-sensitive. How is the regex engine
to know that? And how should it do a case-insensitive match of a
character against the [[:fubar:]] char class? John, can you confirm this
is a legitimate problem?
</p>
<p>
I see two options:
</p>
<p>
1) Add a bool icase parameter to lookup_classname. Then,
lookup_classname( "upper", true ) will know to return lower|upper
instead of just upper.
</p>
<p>
2) Add a isctype_nocase function
</p>
<p>
I prefer (1) because the extra computation happens at the time the
pattern is compiled rather than when it is executed.
</p>
<p>
-- End original message --
</p>
<p>
For what it's worth, John has also expressed his preference for option
(1) above.
</p>
<p><b>Proposed resolution:</b></p>
<hr>
<a name="525"><h3>525.&nbsp;type traits definitions not clear</h3></a><p><b>Section:</b>&nbsp;TR1 4.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.meta.unary"> [tr.meta.unary]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Robert Klarer&nbsp; <b>Date:</b>&nbsp;11 Jul 2005</p>
<p>
It is not completely clear how the primary type traits deal with
cv-qualified types. And several of the secondary type traits
seem to be lacking a definition.
</p>
<p><i>[
Berlin: Howard to provide wording.
]</i></p>
<p><b>Proposed resolution:</b></p>
<hr>
<a name="526"><h3>526.&nbsp;Is it undefined if a function in the standard changes in parameters?</h3></a><p><b>Section:</b>&nbsp;23.1.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.sequence.reqmts"> [lib.sequence.reqmts]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Chris Jefferson&nbsp; <b>Date:</b>&nbsp;14 Sep 2005</p>
<p>
Problem: There are a number of places in the C++ standard library where
it is possible to write what appear to be sensible ways of calling
functions, but which can cause problems in some (or all)
implementations, as they cause the values given to the function to be
changed in a way not specified in standard (and therefore not coded to
correctly work). These fall into two similar categories.
</p>
<p>
1) Parameters taken by const reference can be changed during execution
of the function
</p>
<p>
Examples:
</p>
<p>
Given std::vector&lt;int&gt; v:
</p>
<p>
v.insert(v.begin(), v[2]);
</p>
<p>
v[2] can be changed by moving elements of vector
</p>
<p>
Given std::list&lt;int&gt; l:
</p>
<p>
l.remove(*l.begin());
</p>
<p>
Will delete the first element, and then continue trying to access it.
This is particularily vicious, as it will appear to work in almost all
cases.
</p>
<p>
2) A range is given which changes during the execution of the function:
Similarly,
</p>
<p>
v.insert(v.begin(), v.begin()+4, v.begin()+6);
</p>
<p>
This kind of problem has been partly covered in some cases. For example
std::copy(first, last, result) states that result cannot be in the range
[first, last). However, does this cover the case where result is a
reverse_iterator built from some iterator in the range [first, last)?
Also, std::copy would still break if result was reverse_iterator(last +
1), yet this is not forbidden by the standard
</p>
<p>
Solution:
</p>
<p>
One option would be to try to more carefully limit the requirements of
each function. There are many functions which would have to be checked.
However as has been shown in the std::copy case, this may be difficult.
A simpler, more global option would be to somewhere insert text similar to:
</p>
<p>
If the execution of any function would change either any values passed
by reference or any value in any range passed to a function in a way not
defined in the definition of that function, the result is undefined.
</p>
<p>
Such code would have to at least cover chapters 23 and 25 (the sections
I read through carefully). I can see no harm on applying it to much of
the rest of the standard.
</p>
<p>
Some existing parts of the standard could be improved to fit with this,
for example the requires for 25.2.1 (Copy) could be adjusted to:
</p>
<p>
Requires: For each non-negative integer n &lt; (last - first), assigning to
*(result + n) must not alter any value in the range [first + n, last).
</p>
<p>
However, this may add excessive complication.
</p>
<p>
One other benefit of clearly introducing this text is that it would
allow a number of small optimisations, such as caching values passed
by const reference.
</p>
<p>
Matt Austern adds that this issue also exists for the <tt>insert</tt> and
<tt>erase</tt> members of the ordered and unordered associative containers.
</p>
<p><i>[
Berlin: Lots of controversey over how this should be solved. Lots of confusion
as to whether we're talking about self referencing iterators or references.
Needs a good survey as to the cases where this matters, for which
implementations, and how expensive it is to fix each case.
]</i></p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="527"><h3>527.&nbsp;tr1::bind has lost its Throws clause</h3></a><p><b>Section:</b>&nbsp;TR1 3.6.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.func.bind.bind"> [tr.func.bind.bind]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Peter Dimov&nbsp; <b>Date:</b>&nbsp;01 Oct 2005</p>
<p>
The original bind proposal gives the guarantee that tr1::bind(f, t1,
..., tN) does not throw when the copy constructors of f, t1, ..., tN
don't.
</p>
<p>
This guarantee is not present in the final version of TR1.
</p>
<p>
I'm pretty certain that we never removed it on purpose. Editorial omission? :-)
</p>
<p><i>[
Berlin: not quite editorial, needs proposed wording.
]</i></p>
<p><b>Proposed resolution:</b></p>
<p>
In 20.5.10.1.3 [lib.func.bind.bind] ([tr.func.bind.bind]), add a new paragraph after p2:
</p>
<blockquote>
<i>Throws:</i> Nothing unless one of the copy constructors of <tt>f, t1, t2, ..., tN</tt>
throws an exception.
</blockquote>
<p>
Add a new paragraph after p4:
</p>
<blockquote>
<i>Throws:</i> nothing unless one of the copy constructors of <tt>f, t1, t2, ..., tN</tt>
throws an exception.
</blockquote>
<hr>
<a name="528"><h3>528.&nbsp;TR1: issue 6.19 vs 6.3.4.3/2 (and 6.3.4.5/2)</h3></a><p><b>Section:</b>&nbsp;TR1 6.3.4 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.unord.unord"> [tr.unord.unord]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Paolo Carlini&nbsp; <b>Date:</b>&nbsp;12 Oct 2005</p>
<p>
while implementing the resolution of issue 6.19 I'm noticing the
following: according to 6.3.4.3/2 (and 6.3.4.5/2), for unordered_set and
unordered_multiset:
</p>
<blockquote>
"The iterator and const_iterator types are both const types. It is
unspecified whether they are the same type"
</blockquote>
<p>
Now, according to the resolution of 6.19, we have overloads of insert
with hint and erase (single and range) both for iterator and
const_iterator, which, AFAICS, can be meaningful at the same time *only*
if iterator and const_iterator *are* in fact different types.
</p>
<p>
Then, iterator and const_iterator are *required* to be different types?
Or that is an unintended consequence? Maybe the overloads for plain
iterators should be added only to unordered_map and unordered_multimap?
Or, of course, I'm missing something?
</p>
<p><b>Proposed resolution:</b></p>
<p>
Add to 6.3.4.3p2 (and 6.3.4.5p2):
</p>
<p>
2 ... The iterator and const_iterator types are both <del>const</del>
<ins>constant</ins> iterator types.
It is unspecified whether they are the same type.
</p>
<p>
Add a new subsection to 17.4.4 [lib.conforming]:
</p>
<blockquote>
<p>
An implementation shall not supply an overloaded function
signature specified in any library clause if such a signature
would be inherently ambiguous during overload resolution
due to two library types referring to the same type.
</p>
<p>
[Note: For example, this occurs when a container's iterator
and const_iterator types are the same. -- end note]
</p>
</blockquote>
<p><i>[
Post-Berlin: Beman supplied wording.
]</i></p>
<hr>
<a name="529"><h3>529.&nbsp;The standard encourages redundant and confusing preconditions</h3></a><p><b>Section:</b>&nbsp;17.4.3.8 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-intro.html#lib.res.on.required"> [lib.res.on.required]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;David Abrahams&nbsp; <b>Date:</b>&nbsp;25 Oct 2005</p>
<p>
17.4.3.8/1 says:
</p>
<blockquote>
Violation of the preconditions specified in a function's
Required behavior: paragraph results in undefined behavior unless the
function's Throws: paragraph specifies throwing an exception when the
precondition is violated.
</blockquote>
<p>
This implies that a precondition violation can lead to defined
behavior. That conflicts with the only reasonable definition of
precondition: that a violation leads to undefined behavior. Any other
definition muddies the waters when it comes to analyzing program
correctness, because precondition violations may be routinely done in
correct code (e.g. you can use std::vector::at with the full
expectation that you'll get an exception when your index is out of
range, catch the exception, and continue). Not only is it a bad
example to set, but it encourages needless complication and redundancy
in the standard. For example:
</p>
<blockquote><pre> 21 Strings library
21.3.3 basic_string capacity
void resize(size_type n, charT c);
5 Requires: n &lt;= max_size()
6 Throws: length_error if n &gt; max_size().
7 Effects: Alters the length of the string designated by *this as follows:
</pre></blockquote>
<p>
The Requires clause is entirely redundant and can be dropped. We
could make that simplifying change (and many others like it) even
without changing 17.4.3.8/1; the wording there just seems to encourage
the redundant and error-prone Requires: clause.
</p>
<p><b>Proposed resolution:</b></p>
<p>
1. Change 17.4.3.8/1 to read:
</p>
<blockquote>
Violation of the preconditions specified in a function's
<i>Required behavior:</i> paragraph results in undefined behavior
<del>unless the function's <i>Throws:</i> paragraph specifies throwing
an exception when the precondition is violated</del>.
</blockquote>
<p>
2. Go through and remove redundant Requires: clauses. Specifics to be
provided by Dave A.
</p>
<p><i>[
Berlin: The LWG requests a detailed survey of part 2 of the proposed resolution.
]</i></p>
<hr>
<a name="531"><h3>531.&nbsp;array forms of unformatted input functions</h3></a><p><b>Section:</b>&nbsp;27.6.1.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.istream.unformatted"> [lib.istream.unformatted]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;23 Nov 2005</p>
<p>
The array forms of unformatted input functions don't seem to have well-defined
semantics for zero-element arrays in a couple of cases. The affected ones
(<tt>istream::get()</tt> and <tt>istream::getline()</tt>) are supposed to
terminate when <tt>(n - 1)</tt> characters are stored, which obviously can
never be true when <tt>(n == 0)</tt> holds to start with. See
c++std-lib-16071.
</p>
<p><b>Proposed resolution:</b></p>
<p>
I suggest changing 27.6.1.3, p7 (<tt>istream::get()</tt>), bullet 1 to read:
</p>
<p>
</p><ul>
<li>
<tt>(n &lt; 1)</tt> is true or <tt>(n - 1)</tt> characters
are stored;
</li>
</ul>
<p></p>
<p>
Change 27.6.1.3, p9:
</p>
<blockquote>
If the function stores no characters, it calls <tt>setstate(failbit)</tt> (which
may throw <tt>ios_base::failure</tt> (27.4.4.3)). In any case, <ins>if <tt>(n
&gt; 0)</tt> is true</ins> it then stores a null character into the next
successive location of the array.
</blockquote>
<p>
and similarly p17 (<tt>istream::getline()</tt>), bullet 3 to:
</p>
<p>
</p><ul>
<li>
<tt>(n &lt; 1)</tt> is true or <tt>(n - 1)</tt> characters
are stored (in which case the function calls
<tt>setstate(failbit)</tt>).
</li>
</ul>
<p></p>
<p>
In addition, to clarify that <tt>istream::getline()</tt> must not store the
terminating NUL character unless the the array has non-zero size, Robert
Klarer suggests in c++std-lib-16082 to change 27.6.1.3, p20 to read:
</p>
<p>
</p><blockquote>
In any case, provided <tt>(n &gt; 0)</tt> is true, it then stores a null character
(using charT()) into the next successive location of the array.
</blockquote>
<p></p>
<p><i>[
post-Redmond: Pete noticed that the current resolution for <tt>get</tt> requires
writing to out of bounds memory when <tt>n == 0</tt>. Martin provided fix.
]</i></p>
<hr>
<a name="532"><h3>532.&nbsp;Tuple comparison</h3></a><p><b>Section:</b>&nbsp;TR1 6.1.3.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.tuple.rel"> [tr.tuple.rel]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;David Abrahams&nbsp; <b>Date:</b>&nbsp;29 Nov 2005</p>
<p>
Where possible, tuple comparison operators &lt;,&lt;=,=&gt;, and &gt; ought to be
defined in terms of std::less rather than operator&lt;, in order to
support comparison of tuples of pointers.
</p>
<p><b>Proposed resolution:</b></p>
<p>
change 6.1.3.5/5 from:
</p>
<blockquote>
Returns: The result of a lexicographical comparison between t and
u. The result is defined as: (bool)(get&lt;0&gt;(t) &lt; get&lt;0&gt;(u)) ||
(!(bool)(get&lt;0&gt;(u) &lt; get&lt;0&gt;(t)) &amp;&amp; ttail &lt; utail), where rtail for
some tuple r is a tuple containing all but the first element of
r. For any two zero-length tuples e and f, e &lt; f returns false.
</blockquote>
<p>
to:
</p>
<blockquote>
<p>
Returns: The result of a lexicographical comparison between t and
u. For any two zero-length tuples e and f, e &lt; f returns false.
Otherwise, the result is defined as: cmp( get&lt;0&gt;(t), get&lt;0&gt;(u)) ||
(!cmp(get&lt;0&gt;(u), get&lt;0&gt;(t)) &amp;&amp; ttail &lt; utail), where rtail for some
tuple r is a tuple containing all but the first element of r, and
cmp(x,y) is an unspecified function template defined as follows.
</p>
<p>
Where T is the type of x and U is the type of y:
</p>
<p>
if T and U are pointer types and T is convertible to U, returns
less&lt;U&gt;()(x,y)
</p>
<p>
otherwise, if T and U are pointer types, returns less&lt;T&gt;()(x,y)
</p>
<p>
otherwise, returns (bool)(x &lt; y)
</p>
</blockquote>
<p><i>[
Berlin: This issue is much bigger than just tuple (pair, containers,
algorithms). Dietmar will survey and work up proposed wording.
]</i></p>
<hr>
<a name="534"><h3>534.&nbsp;Missing basic_string members</h3></a><p><b>Section:</b>&nbsp;21.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-strings.html#lib.basic.string"> [lib.basic.string]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Alisdair Meredith&nbsp; <b>Date:</b>&nbsp;16 Nov 2005</p>
<p>
OK, we all know std::basic_string is bloated and already has way too
many members. However, I propose it is missing 3 useful members that
are often expected by users believing it is a close approximation of the
container concept. All 3 are listed in table 71 as 'optional'
</p>
<p>
i/ pop_back.
</p>
<p>
This is the one I feel most strongly about, as I only just discovered it
was missing as we are switching to a more conforming standard library
&lt;g&gt;
</p>
<p>
I find it particularly inconsistent to support push_back, but not
pop_back.
</p>
<p>
ii/ back.
</p>
<p>
There are certainly cases where I want to examine the last character of
a string before deciding to append, or to trim trailing path separators
from directory names etc. *rbegin() somehow feels inelegant.
</p>
<p>
iii/ front
</p>
<p>
This one I don't feel strongly about, but if I can get the first two,
this one feels that it should be added as a 'me too' for consistency.
</p>
<p>
I believe this would be similarly useful to the data() member recently
added to vector, or at() member added to the maps.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Add the following members to definition of class template basic_string, 21.3p7
</p>
<blockquote><pre>void pop_back ()
const charT &amp; front() const
charT &amp; front()
const charT &amp; back() const
charT &amp; back()
</pre></blockquote>
<p>
Add the following paragraphs to basic_string description
</p>
<p>
21.3.4p5
</p>
<blockquote>
<pre>const charT &amp; front() const
charT &amp; front()
</pre>
<p>
<i>Precondition:</i> <tt>!empty()</tt>
</p>
<p>
<i>Effects:</i> Equivalent to <tt>operator[](0)</tt>.
</p>
</blockquote>
<p>
21.3.4p6
</p>
<blockquote>
<pre>const charT &amp; back() const
charT &amp; back()
</pre>
<p>
<i>Precondition:</i> <tt>!empty()</tt>
</p>
<p>
<i>Effects:</i> Equivalent to <tt>operator[]( size() - 1)</tt>.
</p>
</blockquote>
<p>
21.3.5.5p10
</p>
<blockquote>
<pre>void pop_back ()
</pre>
<p>
<i>Precondition:</i> <tt>!empty()</tt>
</p>
<p>
<i>Effects:</i> Equivalent to <tt>erase( size() - 1, 1 )</tt>.
</p>
</blockquote>
<p>
Update Table 71: (optional sequence operations)
Add basic_string to the list of containers for the following operations.
</p>
<blockquote><pre>a.front()
a.back()
a.push_back()
a.pop_back()
a[n]
</pre></blockquote>
<p><i>[
Berlin: Has support. Alisdair provided wording.
]</i></p>
<hr>
<a name="536"><h3>536.&nbsp;Container iterator constructor and explicit convertibility</h3></a><p><b>Section:</b>&nbsp;23.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Joaqu<EFBFBD>n M L<>pez Mu<4D>oz&nbsp; <b>Date:</b>&nbsp;17 Dec 2005</p>
<p>
The iterator constructor X(i,j) for containers as defined in 23.1.1 and
23.2.2 does only require that i and j be input iterators but
nothing is said about their associated value_type. There are three
sensible
options:
</p>
<ol>
<li>iterator's value_type is exactly X::value_type (modulo cv).</li>
<li>iterator's value_type is *implicitly* convertible to X::value_type.</li>
<li>iterator's value_type is *explicitly* convertible to X::value_type.</li>
</ol>
<p>
The issue has practical implications, and stdlib vendors have
taken divergent approaches to it: Dinkumware follows 2,
libstdc++ follows 3.
</p>
<p>
The same problem applies to the definition of insert(p,i,j) for
sequences and insert(i,j) for associative contianers, as well as
assign.
</p>
<p><i>[
The following added by Howard and the example code was originally written by
Dietmar.
]</i></p>
<p>
Valid code below?
</p>
<blockquote><pre>#include &lt;vector&gt;
#include &lt;iterator&gt;
#include &lt;iostream&gt;
struct foo
{
explicit foo(int) {}
};
int main()
{
std::vector&lt;int&gt; v_int;
std::vector&lt;foo&gt; v_foo1(v_int.begin(), v_int.end());
std::vector&lt;foo&gt; v_foo2((std::istream_iterator&lt;int&gt;(std::cin)),
std::istream_iterator&lt;int&gt;());
}
</pre></blockquote>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<p><i>[
Berlin: Some support, not universal, for respecting the explicit qualifier.
]</i></p>
<hr>
<a name="539"><h3>539.&nbsp;partial_sum and adjacent_difference should mention requirements</h3></a><p><b>Section:</b>&nbsp;26.4 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.rand"> [lib.rand]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Marc Schoolderman&nbsp; <b>Date:</b>&nbsp;6 Feb 2006</p>
<p>
There are some problems in the definition of partial_sum and
adjacent_difference in 26.4 [lib.numeric.ops]
</p>
<p>
Unlike <tt>accumulate</tt> and <tt>inner_product</tt>, these functions are not
parametrized on a "type T", instead, 26.4.3 [lib.partial.sum] simply
specifies the effects clause as;
</p>
<blockquote>
Assigns to every element referred to by iterator <tt>i</tt> in the range
<tt>[result,result + (last - first))</tt> a value correspondingly equal to
<blockquote><pre>((...(* first + *( first + 1)) + ...) + *( first + ( i - result )))
</pre></blockquote>
</blockquote>
<p>
And similarly for BinaryOperation. Using just this definition, it seems
logical to expect that:
</p>
<blockquote><pre>char i_array[4] = { 100, 100, 100, 100 };
int o_array[4];
std::partial_sum(i_array, i_array+4, o_array);
</pre></blockquote>
<p>
Is equivalent to
</p>
<blockquote><pre>int o_array[4] = { 100, 100+100, 100+100+100, 100+100+100+100 };
</pre></blockquote>
<p>
i.e. 100, 200, 300, 400, with addition happening in the <tt>result type</tt>,
<tt>int</tt>.
</p>
<p>
Yet all implementations I have tested produce 100, -56, 44, -112,
because they are using an accumulator of the <tt>InputIterator</tt>'s
<tt>value_type</tt>, which in this case is <tt>char</tt>, not <tt>int</tt>.
</p>
<p>
The issue becomes more noticeable when the result of the expression <tt>*i +
*(i+1)</tt> or <tt>binary_op(*i, *i-1)</tt> can't be converted to the
<tt>value_type</tt>. In a contrived example:
</p>
<blockquote><pre>enum not_int { x = 1, y = 2 };
...
not_int e_array[4] = { x, x, y, y };
std::partial_sum(e_array, e_array+4, o_array);
</pre></blockquote>
<p>
Is it the intent that the operations happen in the <tt>input type</tt>, or in
the <tt>result type</tt>?
</p>
<p>
If the intent is that operations happen in the <tt>result type</tt>, something
like this should be added to the "Requires" clause of 26.4.3/4
[lib.partial.sum]:
</p>
<blockquote>
The type of <tt>*i + *(i+1)</tt> or <tt>binary_op(*i, *(i+1))</tt> shall meet the
requirements of <tt>CopyConstructible</tt> (20.1.3) and <tt>Assignable</tt>
(23.1) types.
</blockquote>
<p>
(As also required for <tt>T</tt> in 26.4.1 [lib.accumulate] and 26.4.2
[lib.inner.product].)
</p>
<p>
The "auto initializer" feature proposed in
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1894.pdf">N1894</a>
is not required to
implement <tt>partial_sum</tt> this way. The 'narrowing' behaviour can still be
obtained by using the <tt>std::plus&lt;&gt;</tt> function object.
</p>
<p>
If the intent is that operations happen in the <tt>input type</tt>, then
something like this should be added instead;
</p>
<blockquote>
The type of *first shall meet the requirements of
<tt>CopyConstructible</tt> (20.1.3) and <tt>Assignable</tt> (23.1) types.
The result of <tt>*i + *(i+1)</tt> or <tt>binary_op(*i, *(i+1))</tt> shall be
convertible to this type.
</blockquote>
<p>
The 'widening' behaviour can then be obtained by writing a custom proxy
iterator, which is somewhat involved.
</p>
<p>
In both cases, the semantics should probably be clarified.
</p>
<p>
26.4.4 [lib.adjacent.difference] is similarly underspecified, although
all implementations seem to perform operations in the 'result' type:
</p>
<blockquote><pre>unsigned char i_array[4] = { 4, 3, 2, 1 };
int o_array[4];
std::adjacent_difference(i_array, i_array+4, o_array);
</pre></blockquote>
<p>
o_array is 4, -1, -1, -1 as expected, not 4, 255, 255, 255.
</p>
<p>
In any case, <tt>adjacent_difference</tt> doesn't mention the requirements on the
<tt>value_type</tt>; it can be brought in line with the rest of 26.4
[lib.numeric.ops] by adding the following to 26.4.4/2
[lib.adjacent.difference]:
</p>
<blockquote>
The type of <tt>*first</tt> shall meet the requirements of
<tt>CopyConstructible</tt> (20.1.3) and <tt>Assignable</tt> (23.1) types."
</blockquote>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<p><i>[
Berlin: Giving output iterator's value_types very controversial. Suggestion of
adding signatures to allow user to specify "accumulator".
]</i></p>
<hr>
<a name="542"><h3>542.&nbsp;shared_ptr observers</h3></a><p><b>Section:</b>&nbsp;TR1 2.2.3.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.util.smartptr.shared.obs"> [tr.util.smartptr.shared.obs]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;18 Oct 2005</p>
<p>
Peter Dimov wrote:
To: C++ libraries mailing list
Message c++std-lib-15614
[...]
The intent is for both use_count() and unique() to work in a threaded environment.
They are intrinsically prone to race conditions, but they never return garbage.
</p>
<p>
This is a crucial piece of information that I really wish were
captured in the text. Having this in a non-normative note would
have made everything crystal clear to me and probably stopped
me from ever starting this discussion :) Instead, the sentence
in p12 "use only for debugging and testing purposes, not for
production code" very strongly suggests that implementations
can and even are encouraged to return garbage (when threads
are involved) for performance reasons.
</p>
<p>
How about adding an informative note along these lines:
</p>
<blockquote>
Note: Implementations are encouraged to provide well-defined
behavior for use_count() and unique() even in the presence of
multiple threads.
</blockquote>
<p>
I don't necessarily insist on the exact wording, just that we
capture the intent.
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="543"><h3>543.&nbsp;valarray slice default constructor</h3></a><p><b>Section:</b>&nbsp;26.3.4 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.complex.members"> [lib.complex.members]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Howard Hinnant&nbsp; <b>Date:</b>&nbsp;3 Nov 2005</p>
<p>
If one explicitly constructs a slice or glice with the default
constructor, does the standard require this slice to have any usable
state? It says "creates a slice which specifies no elements", which
could be interpreted two ways:
</p>
<ol>
<li>There are no elements to which the slice refers (i.e. undefined).</li>
<li>The slice specifies an array with no elements in it (i.e. defined).</li>
</ol>
<p>
Here is a bit of code to illustrate:
</p>
<blockquote><pre>#include &lt;iostream&gt;
#include &lt;valarray&gt;
int main()
{
std::valarray&lt;int&gt; v(10);
std::valarray&lt;int&gt; v2 = v[std::slice()];
std::cout &lt;&lt; "v[slice()].size() = " &lt;&lt; v2.size() &lt;&lt; '\n';
}
</pre></blockquote>
<p>
Is the behavior undefined? Or should the output be:
</p>
<blockquote>
v[slice()].size() = 0
</blockquote>
<p>
There is a similar question and wording for gslice at 26.3.6.1p1.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change 26.5.4.1 [cons.slice]:
</p>
<blockquote>
1 - <del>The default constructor for <tt>slice</tt> creates a <tt>slice</tt>
which specifies no elements.</del> <ins>The default constructor is equivalent to
<tt>slice(0, 0, 0)</tt>.</ins> A default constructor is provided only to permit
the declaration of arrays of slices. The constructor with arguments for a slice
takes a start, length, and stride parameter.
</blockquote>
<p>
Change 26.3.6.1 [gslice.cons]:
</p>
<blockquote>
1 - <del>The default constructor creates a <tt>gslice</tt> which specifies no
elements.</del> <ins>The default constructor is equivalent to <tt>gslice(0,
valarray&lt;size_t&gt;(), valarray&lt;size_t&gt;())</tt>.</ins> The constructor
with arguments builds a <tt>gslice</tt> based on a specification of start,
lengths, and strides, as explained in the previous section.
</blockquote>
<hr>
<a name="545"><h3>545.&nbsp;When is a deleter deleted?</h3></a><p><b>Section:</b>&nbsp;TR1 2.2.3.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.util.smartptr.shared.dest"> [tr.util.smartptr.shared.dest]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;10 Jan 2006</p>
<p>
The description of ~shared_ptr doesn't say when the shared_ptr's deleter, if
any, is destroyed. In principle there are two possibilities: it is destroyed
unconditionally whenever ~shared_ptr is executed (which, from an implementation
standpoint, means that the deleter is copied whenever the shared_ptr is copied),
or it is destroyed immediately after the owned pointer is destroyed (which, from
an implementation standpoint, means that the deleter object is shared between
instances). We should say which it is.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Add after the first sentence of [lib.util.smartptr.getdeleter]/1:
</p>
<blockquote>
<p>
The returned pointer remains valid as long as there exists a <tt>shared_ptr</tt> instance
that owns <tt><i>d</i></tt>.
</p>
<p>
[<i>Note:</i> it is unspecified whether the pointer remains valid longer than that.
This can happen if the implementation doesn't destroy the deleter until all
<tt>weak_ptr</tt> instances in the ownership group are destroyed. <i>-- end note</i>]
</p>
</blockquote>
<hr>
<a name="546"><h3>546.&nbsp;_Longlong and _ULonglong are integer types</h3></a><p><b>Section:</b>&nbsp;TR1 5.1.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.rand.req"> [tr.rand.req]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;10 Jan 2006</p>
<p>
The TR sneaks in two new integer types, _Longlong and _Ulonglong, in [tr.c99].
The rest of the TR should use that type.&nbsp; I believe this affects two places.
First, the random number requirements, 5.1.1/10-11, lists all of the types with
which template parameters named IntType and UIntType may be instantiated.
_Longlong (or "long long", assuming it is added to C++0x) should be added to the
IntType list, and UIntType (again, or "unsigned long long") should be added to
the UIntType list.&nbsp; Second, 6.3.2 lists the types for which hash&lt;&gt; is
required to be instantiable. _Longlong and _Ulonglong should be added to that
list, so that people may use long long as a hash key.
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="547"><h3>547.&nbsp;division should be floating-point, not integer</h3></a><p><b>Section:</b>&nbsp;TR1 5.1.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.rand.var"> [tr.rand.var]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;10 Jan 2006</p>
<p>
Paragraph 10 describes how a variate generator uses numbers produced by an
engine to pass to a generator. The sentence that concerns me is: "Otherwise, if
the value for engine_value_type::result_type is true and the value for
Distribution::input_type is false [i.e. if the engine produces integers and the
engine wants floating-point values], then the numbers in s_eng are divided by
engine().max() - engine().min() + 1 to obtain the numbers in s_e." Since the
engine is producing integers, both the numerator and the denominator are
integers and we'll be doing integer division, which I don't think is what we
want. Shouldn't we be performing a conversion to a floating-point type first?
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="548"><h3>548.&nbsp;May random_device block?</h3></a><p><b>Section:</b>&nbsp;TR1 5.1.6 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.rand.device"> [tr.rand.device]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Matt Austern&nbsp; <b>Date:</b>&nbsp;10 Jan 2006</p>
<p>
Class random_device "produces non-deterministic random numbers", using some
external source of entropy. In most real-world systems, the amount of available
entropy is limited. Suppose that entropy has been exhausted. What is an
implementation permitted to do? In particular, is it permitted to block
indefinitely until more random bits are available, or is the implementation
required to detect failure immediately? This is not an academic question. On
Linux a straightforward implementation would read from /dev/random, and "When
the entropy pool is empty, reads to /dev/random will block until additional
environmental noise is gathered." Programmers need to know whether random_device
is permitted to (or possibly even required to?) behave the same way.
</p>
<p><i>[
Berlin: Walter: N1932 considers this NAD. Does the standard specify whether std::cin
may block?
]</i></p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="550"><h3>550.&nbsp;What should the return type of pow(float,int) be?</h3></a><p><b>Section:</b>&nbsp;26.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.numarray"> [lib.numarray]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Howard Hinnant&nbsp; <b>Date:</b>&nbsp;12 Jan 2006</p>
<p>
Assuming we adopt the
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf">C
compatibility package from C99</a> what should be the return type of the
following signature be:
</p>
<blockquote><pre>? pow(float, int);
</pre></blockquote>
<p>
C++03 says that the return type should be <tt>float</tt>.
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf">
TR1</a> and C90/99 say the return type should be <tt>double</tt>. This can put
clients into a situation where C++03 provides answers that are not as high
quality as C90/C99/TR1. For example:
</p>
<blockquote><pre>#include &lt;math.h&gt;
int main()
{
float x = 2080703.375F;
double y = pow(x, 2);
}
</pre></blockquote>
<p>
Assuming an IEEE 32 bit float and IEEE 64 bit double, C90/C99/TR1 all suggest:
</p>
<blockquote><pre>y = 4329326534736.390625
</pre></blockquote>
<p>
which is exactly right. While C++98/C++03 demands:
</p>
<blockquote><pre>y = 4329326510080.
</pre></blockquote>
<p>
which is only approximately right.
</p>
<p>
I recommend that C++0X adopt the mixed mode arithmetic already adopted by
Fortran, C and TR1 and make the return type of <tt>pow(float,int)</tt> be
<tt>double</tt>.
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="551"></a><h3><a name="551">551.&nbsp;&lt;ccomplex&gt;</a></h3><p><b>Section:</b>&nbsp;TR1 8.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.c99.ccmplx"> [tr.c99.ccmplx]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Howard Hinnant&nbsp; <b>Date:</b>&nbsp;23 Jan 2006</p>
<p>
Previously xxx.h was parsable by C++. But in the case of C99's &lt;complex.h&gt;
it isn't. Otherwise we could model it just like &lt;string.h&gt;, &lt;cstring&gt;, &lt;string&gt;:
</p>
<ul>
<li>&lt;string&gt; : C++ API in namespace std</li>
<li>&lt;cstring&gt; : C API in namespace std</li>
<li>&lt;string.h&gt; : C API in global namespace</li>
</ul>
<p>
In the case of C's complex, the C API won't compile in C++. So we have:
</p>
<ul>
<li>&lt;complex&gt; : C++ API in namespace std</li>
<li>&lt;ccomplex&gt; : ?</li>
<li>&lt;complex.h&gt; : ?</li>
</ul>
<p>
The ? can't refer to the C API. TR1 currently says:
</p>
<ul>
<li>&lt;complex&gt; : C++ API in namespace std</li>
<li>&lt;ccomplex&gt; : C++ API in namespace std</li>
<li>&lt;complex.h&gt; : C++ API in global namespace</li>
</ul>
<p><b>Proposed resolution:</b></p>
<p>
Change 26.3.11 [cmplxh]:
</p>
<blockquote>
<p>
The header behaves as if it includes the header
<tt>&lt;ccomplex&gt;</tt><ins>.</ins><del>, and provides sufficient using
declarations to declare in the global namespace all function and type names
declared or defined in the neader <tt>&lt;complex&gt;</tt>.</del>
<ins>[<i>Note:</i> <tt>&lt;complex.h&gt;</tt> does not promote any interface
into the global namespace as there is no C interface to promote. <i>--end
note</i>]</ins>
</p>
</blockquote>
<hr>
<a name="552"><h3>552.&nbsp;random_shuffle and its generator</h3></a><p><b>Section:</b>&nbsp;25.2.11 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-algorithms.html#lib.alg.random.shuffle"> [lib.alg.random.shuffle]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;25 Jan 2006</p>
<p>
...is specified to shuffle its range by calling swap but not how
(or even that) it's supposed to use the RandomNumberGenerator
argument passed to it.
</p>
<p>
Shouldn't we require that the generator object actually be used
by the algorithm to obtain a series of random numbers and specify
how many times its operator() should be invoked by the algorithm?
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="553"><h3>553.&nbsp;very minor editorial change intptr_t / uintptr_t</h3></a><p><b>Section:</b>&nbsp;TR1 8.22.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.c99.cstdint.syn"> [tr.c99.cstdint.syn]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Paolo Carlini&nbsp; <b>Date:</b>&nbsp;30 Jan 2006</p>
<p>
In the synopsis, some types are identified as optional: int8_t, int16_t,
and so on, consistently with C99, indeed.
</p>
<p>
On the other hand, intptr_t and uintptr_t, are not marked as such and
probably should, consistently with C99, 7.18.1.4.
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="556"><h3>556.&nbsp;is Compare a BinaryPredicate?</h3></a><p><b>Section:</b>&nbsp;25.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-algorithms.html#lib.alg.sorting"> [lib.alg.sorting]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;5 Feb 2006</p>
<p>
In 25, p8 we allow BinaryPredicates to return a type that's convertible
to bool but need not actually be bool. That allows predicates to return
things like proxies and requires that implementations be careful about
what kinds of expressions they use the result of the predicate in (e.g.,
the expression in if (!pred(a, b)) need not be well-formed since the
negation operator may be inaccessible or return a type that's not
convertible to bool).
</p>
<p>
Here's the text for reference:
</p>
<blockquote>
...if an algorithm takes BinaryPredicate binary_pred as its argument
and first1 and first2 as its iterator arguments, it should work
correctly in the construct if (binary_pred(*first1, first2)){...}.
</blockquote>
<p>
In 25.3, p2 we require that the Compare function object return true
of false, which would seem to preclude such proxies. The relevant text
is here:
</p>
<blockquote>
Compare is used as a function object which returns true if the first
argument is less than the second, and false otherwise...
</blockquote>
<p><b>Proposed resolution:</b></p>
<p>
I think we could fix this by rewording 25.3, p2 to read somthing like:
</p>
<blockquote>
-2- <tt>Compare</tt> is <del>used as a function object which returns
<tt>true</tt> if the first argument</del> <ins>a <tt>BinaryPredicate</tt>. The
return value of the function call operator applied to an object of type
<tt>Compare</tt>, when converted to type <tt>bool</tt>, yields <tt>true</tt>
if the first argument of the call</ins> is less than the second, and
<tt>false</tt> otherwise. <tt>Compare <i>comp</i></tt> is used throughout for
algorithms assuming an ordering relation. It is assumed that <tt><i>comp</i></tt>
will not apply any non-constant function through the dereferenced iterator.
</blockquote>
<hr>
<a name="557"><h3>557.&nbsp;TR1: div(_Longlong, _Longlong) vs div(intmax_t, intmax_t)</h3></a><p><b>Section:</b>&nbsp;TR1 8.11.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.c99.cinttypes.syn"> [tr.c99.cinttypes.syn]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Paolo Carlini&nbsp; <b>Date:</b>&nbsp;6 Feb 2006</p>
<p>
I'm seeing a problem with such overloads: when, _Longlong == intmax_t ==
long long we end up, essentially, with the same arguments and different
return types (lldiv_t and imaxdiv_t, respectively). Similar issue with
abs(_Longlong) and abs(intmax_t), of course.
</p>
<p>
Comparing sections 8.25 and 8.11, I see an important difference,
however: 8.25.3 and 8.25.4 carefully describe div and abs for _Longlong
types (rightfully, because not moved over directly from C99), whereas
there is no equivalent in 8.11: the abs and div overloads for intmax_t
types appear only in the synopsis and are not described anywhere, in
particular no mention in 8.11.2 (at variance with 8.25.2).
</p>
<p>
I'm wondering whether we really, really, want div and abs for intmax_t...
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change the <tt>&lt;cstdint&gt;</tt> synopsis in 8.11.1:
</p>
<blockquote><pre>...
intmax_t imaxabs(intmax_t i);
<del>intmax_t abs(intmax_t i);</del>
imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
<del>imaxdiv_t div(intmax_t numer, intmax_t denom);</del>
...
</pre></blockquote>
<p><i>[
Portland: no consensus.
]</i></p>
<hr>
<a name="559"><h3>559.&nbsp;numeric_limits&lt;const T&gt;</h3></a><p><b>Section:</b>&nbsp;18.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-support.html#lib.support.limits"> [lib.support.limits]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;19 Feb 2006</p>
<p>
18.2.1, p2 requires implementations to provide specializations of the
<code>numeric_limits</code> template for each scalar type. While this
could be interepreted to include cv-qualified forms of such types such
an interepretation is not reflected in the synopsis of the
<code>&lt;limits&gt;</code> header.
</p>
<p>
The absence of specializations of the template on cv-qualified forms
of fundamental types makes <code>numeric_limits</code> difficult to
use in generic code where the constness (or volatility) of a type is
not always immediately apparent. In such contexts, the primary
template ends up being instantiated instead of the provided
specialization, typically yielding unexpected behavior.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Require that specializations of <code>numeric_limits</code> on
cv-qualified fundamental types have the same semantics as those on the
unqualifed forms of the same types.
</p>
<p>
Add to the synopsis of the <code>&lt;limits&gt;</code> header,
immediately below the declaration of the primary template, the
following:
</p><pre>
template &lt;class T&gt; class numeric_limits&lt;const T&gt;;
template &lt;class T&gt; class numeric_limits&lt;volatile T&gt;;
template &lt;class T&gt; class numeric_limits&lt;const volatile T&gt;;
</pre>
<p></p>
<p>
Add a new paragraph to the end of 18.2.1.1, with the following
text:
</p>
<p>
-new-para- The value of each member of a <code>numeric_limits</code>
specialization on a cv-qualified T is equal to the value of the same
member of <code>numeric_limits&lt;T&gt;</code>.
</p>
<p><i>[
Portland: Martin will clarify that user-defined types get cv-specializations
automatically.
]</i></p>
<hr>
<a name="560"><h3>560.&nbsp;User-defined allocators without default constructor</h3></a><p><b>Section:</b>&nbsp;20.1.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.default.con.req"> [lib.default.con.req]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Sergey P. Derevyago&nbsp; <b>Date:</b>&nbsp;17 Feb 2006</p>
<h4>1. The essence of the problem.</h4>
<p>
User-defined allocators without default constructor are not explicitly
supported by the standard but they can be supported just like std::vector
supports elements without default constructor.
</p>
<p>
As a result, there exist implementations that work well with such allocators
and implementations that don't.
</p>
<h4>2. The cause of the problem.</h4>
<p>
1) The standard doesn't explicitly state this intent but it should. In
particular, 20.1.5p5 explicitly state the intent w.r.t. the allocator
instances that compare non-equal. So it can similarly state the intent w.r.t.
the user-defined allocators without default constructor.
</p>
<p>
2) Some container operations are obviously underspecified. In particular,
21.3.7.1p2 tells:
</p>
<blockquote>
<pre>template&lt;class charT, class traits, class Allocator&gt;
basic_string&lt;charT,traits,Allocator&gt; operator+(
const charT* lhs,
const basic_string&lt;charT,traits,Allocator&gt;&amp; rhs
);
</pre>
Returns: <tt>basic_string&lt;charT,traits,Allocator&gt;(lhs) + rhs</tt>.
</blockquote>
<p>
That leads to the basic_string&lt;charT,traits,Allocator&gt;(lhs, Allocator()) call.
Obviously, the right requirement is:
</p>
<blockquote>
Returns: <tt>basic_string&lt;charT,traits,Allocator&gt;(lhs, rhs.get_allocator()) + rhs</tt>.
</blockquote>
<p>
It seems like a lot of DRs can be submitted on this "Absent call to
get_allocator()" topic.
</p>
<h4>3. Proposed actions.</h4>
<p>
1) Explicitly state the intent to allow for user-defined allocators without
default constructor in 20.1.5 Allocator requirements.
</p>
<p>
2) Correct all the places, where a correct allocator object is available
through the get_allocator() call but default Allocator() gets passed instead.
</p>
<h4>4. Code sample.</h4>
<p>
Let's suppose that the following memory pool is available:
</p>
<blockquote><pre>class mem_pool {
// ...
void* allocate(size_t size);
void deallocate(void* ptr, size_t size);
};
</pre></blockquote>
<p>
So the following allocator can be implemented via this pool:
</p>
<blockquote><pre>class stl_allocator {
mem_pool&amp; pool;
public:
explicit stl_allocator(mem_pool&amp; mp) : pool(mp) {}
stl_allocator(const stl_allocator&amp; sa) : pool(sa.pool) {}
template &lt;class U&gt;
stl_allocator(const stl_allocator&lt;U&gt;&amp; sa) : pool(sa.get_pool()) {}
~stl_allocator() {}
pointer allocate(size_type n, std::allocator&lt;void&gt;::const_pointer = 0)
{
return (n!=0) ? static_cast&lt;pointer&gt;(pool.allocate(n*sizeof(T))) : 0;
}
void deallocate(pointer p, size_type n)
{
if (n!=0) pool.deallocate(p, n*sizeof(T));
}
// ...
};
</pre></blockquote>
<p>
Then the following code works well on some implementations and doesn't work on
another:
</p>
<blockquote><pre>typedef basic_string&lt;char, char_traits&lt;char&gt;, stl_allocator&lt;char&gt; &gt;
tl_string;
mem_pool mp;
tl_string s1("abc", stl_allocator&lt;int&gt;(mp));
printf("(%s)\n", ("def"+s1).c_str());
</pre></blockquote>
<p>
In particular, on some implementations the code can't be compiled without
default stl_allocator() constructor.
</p>
<p>
The obvious way to solve the compile-time problems is to intentionally define
a NULL pointer dereferencing default constructor
</p>
<blockquote><pre>stl_allocator() : pool(*static_cast&lt;mem_pool*&gt;(0)) {}
</pre></blockquote>
<p>
in a hope that it will not be called. The problem is that it really gets
called by operator+(const char*, const string&amp;) under the current 21.3.7.1p2
wording.
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="561"><h3>561.&nbsp;inserter overly generic</h3></a><p><b>Section:</b>&nbsp;24.4.2.6.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iterators.html#lib.inserter"> [lib.inserter]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Howard Hinnant&nbsp; <b>Date:</b>&nbsp;21 Feb 2006</p>
<p>
The declaration of <tt>std::inserter</tt> is:
</p>
<blockquote><pre>template &lt;class Container, class Iterator&gt;
insert_iterator&lt;Container&gt;
inserter(Container&amp; x, Iterator i);
</pre></blockquote>
<p>
The template parameter <tt>Iterator</tt> in this function is completely unrelated
to the template parameter <tt>Container</tt> when it doesn't need to be. This
causes the code to be overly generic. That is, any type at all can be deduced
as <tt>Iterator</tt>, whether or not it makes sense. Now the same is true of
<tt>Container</tt>. However, for every free (unconstrained) template parameter
one has in a signature, the opportunity for a mistaken binding grows geometrically.
</p>
<p>
It would be much better if <tt>inserter</tt> had the following signature instead:
</p>
<blockquote><pre>template &lt;class Container&gt;
insert_iterator&lt;Container&gt;
inserter(Container&amp; x, typename Container::iterator i);
</pre></blockquote>
<p>
Now there is only one free template parameter. And the second argument to
<tt>inserter</tt> must be implicitly convertible to the container's iterator,
else the call will not be a viable overload (allowing other functions in the
overload set to take precedence). Furthermore, the first parameter must have a
nested type named <tt>iterator</tt>, or again the binding to <tt>std::inserter</tt>
is not viable. Contrast this with the current situation
where any type can bind to <tt>Container</tt> or <tt>Iterator</tt> and those
types need not be anything closely related to containers or iterators.
</p>
<p>
This can adversely impact well written code. Consider:
</p>
<blockquote><pre>#include &lt;iterator&gt;
#include &lt;string&gt;
namespace my
{
template &lt;class String&gt;
struct my_type {};
struct my_container
{
template &lt;class String&gt;
void push_back(const my_type&lt;String&gt;&amp;);
};
template &lt;class String&gt;
void inserter(const my_type&lt;String&gt;&amp; m, my_container&amp; c) {c.push_back(m);}
} // my
int main()
{
my::my_container c;
my::my_type&lt;std::string&gt; m;
inserter(m, c);
}
</pre></blockquote>
<p>
Today this code fails because the call to <tt>inserter</tt> binds to
<tt>std::inserter</tt> instead of to <tt>my::inserter</tt>. However with the
proposed change <tt>std::inserter</tt> will no longer be a viable function which
leaves only <tt>my::inserter</tt> in the overload resolution set. Everything
works as the client intends.
</p>
<p>
To make matters a little more insidious, the above example works today if you
simply change the first argument to an rvalue:
</p>
<blockquote><pre> inserter(my::my_type(), c);
</pre></blockquote>
<p>
It will also work if instantiated with some string type other than
<tt>std::string</tt> (or any other <tt>std</tt> type). It will also work if
<tt>&lt;iterator&gt;</tt> happens to not get included.
</p>
<p>
And it will fail again for such inocuous reaons as <tt>my_type</tt> or
<tt>my_container</tt> privately deriving from any <tt>std</tt> type.
</p>
<p>
It seems unfortunate that such simple changes in the client's code can result
in such radically differing behavior.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change 24.2:
</p>
<blockquote>
<b>24.2 Header</b> <tt>&lt;iterator&gt;</tt> <b>synopsis</b>
<blockquote><pre>...
template &lt;class Container<del>, class Iterator</del>&gt;
insert_iterator&lt;Container&gt; inserter(Container&amp; x, <del>Iterator</del> <ins>typename Container::iterator</ins> i);
...
</pre></blockquote>
</blockquote>
<p>
Change 24.4.2.5:
</p>
<blockquote>
<b>24.4.2.5 Class template</b> <tt>insert_iterator</tt>
<blockquote><pre>...
template &lt;class Container<del>, class Iterator</del>&gt;
insert_iterator&lt;Container&gt; inserter(Container&amp; x, <del>Iterator</del> <ins>typename Container::iterator</ins> i);
...
</pre></blockquote>
</blockquote>
<p>
Change 24.4.2.6.5:
</p>
<blockquote>
<p>
<b>24.4.2.6.5</b> <tt>inserter</tt>
</p>
<pre>template &lt;class Container<del>, class Inserter</del>&gt;
insert_iterator&lt;Container&gt; inserter(Container&amp; x, <del>Inserter</del> <ins>typename Container::iterator</ins> i);
</pre>
<blockquote>
-1- <i>Returns:</i> <tt>insert_iterator&lt;Container&gt;(x,<del>typename Container::iterator(</del>i<del>)</del>)</tt>.
</blockquote>
</blockquote>
<hr>
<a name="562"><h3>562.&nbsp;stringbuf ctor inefficient</h3></a><p><b>Section:</b>&nbsp;27.7 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.string.streams"> [lib.string.streams]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;23 Feb 2006</p>
<p>
For better efficiency, the requirement on the stringbuf ctor that
takes a string argument should be loosened up to let it set
<code>epptr()</code> beyond just one past the last initialized
character just like <code>overflow()</code> has been changed to be
allowed to do (see issue 432). That way the first call to
<code>sputc()</code> on an object won't necessarily cause a call to
<code>overflow</code>. The corresponding change should be made to the
string overload of the <code>str()</code> member function.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change 27.7.1.1, p3 of the Working Draft, N1804, as follows:
</p>
<blockquote>
<pre>explicit basic_stringbuf(const basic_string&lt;charT,traits,Allocator&gt;&amp; <i>s<del>tr</del></i>,
ios_base::openmode <i>which</i> = ios_base::in | ios_base::out);
</pre>
<p>
-3- <i>Effects:</i> Constructs an object of class <tt>basic_stringbuf</tt>,
initializing the base class with <tt>basic_streambuf()</tt>
(27.5.2.1), and initializing <tt><i>mode</i></tt> with <tt><i>which</i></tt>.
Then <ins>calls <tt>str(<i>s</i>)</tt>.</ins> <del>copies the content of
<i>str</i> into the <tt>basic_stringbuf</tt> underlying character
sequence. If <tt><i>which</i> &amp; ios_base::out</tt> is true, initializes the
output sequence such that <tt>pbase()</tt> points to the first underlying
character, <tt>epptr()</tt> points one past the last underlying character, and
<tt>pptr()</tt> is equal to <tt>epptr()</tt> if <tt><i>which</i> &amp; ios_base::ate</tt>
is true, otherwise <tt>pptr()</tt> is equal to <tt>pbase()</tt>. If
<tt>which &amp; ios_base::in</tt> is true, initializes the input sequence such
that <tt>eback()</tt> and <tt>gptr()</tt> point to the first underlying
character and <tt>egptr()</tt> points one past the last underlying character.</del>
</p>
</blockquote>
<p>
Change the Effects clause of the <code>str()</code> in 27.7.1.2, p2 to
read:
</p>
<blockquote>
<p>
-2- <i>Effects:</i> Copies the content<ins>s</ins> of <tt><i>s</i></tt> into the
<tt>basic_stringbuf</tt> underlying character sequence <ins>and
initializes the input and output sequences according to <tt><i>mode</i></tt></ins>.
<del>If
<tt><i>mode</i> &amp; ios_base::out</tt> is true, initializes the output
sequence such that <tt>pbase()</tt> points to the first underlying character,
<tt>epptr()</tt> points one past the last underlying character, and <tt>pptr()</tt>
is equal to <tt>epptr()</tt> if <tt><i>mode</i> &amp; ios_base::in</tt>
is true, otherwise <tt>pptr()</tt> is equal to <tt>pbase()</tt>. If
<tt>mode &amp; ios_base::in</tt> is true, initializes the input sequence
such that <tt>eback()</tt> and <tt>gptr()</tt> point to the first underlying
character and <tt>egptr()</tt> points one past the last underlying character.</del>
</p>
<p>
<ins>-3- <i>Postconditions:</i> If <code>mode &amp; ios_base::out</code> is true,
<code>pbase()</code> points to the first underlying character and
<code>(epptr() &gt;= pbase() + s.size())</code> holds; in addition, if
<code>mode &amp; ios_base::in</code> is true, <code>(pptr() == pbase()
+ s.data())</code> holds, otherwise <code>(pptr() == pbase())</code>
is true. If <code>mode &amp; ios_base::in</code> is true,
<code>eback()</code> points to the first underlying character, and
<code>(gptr() == eback())</code> and <code>(egptr() == eback() +
s.size())</code> hold.</ins>
</p>
</blockquote>
<hr>
<a name="563"><h3>563.&nbsp;stringbuf seeking from end</h3></a><p><b>Section:</b>&nbsp;27.7.1.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.stringbuf.virtuals"> [lib.stringbuf.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;23 Feb 2006</p>
<p>
According to Table 92 (unchanged by issue 432), when <code>(way ==
end)</code> the <code>newoff</code> value in out mode is computed as
the difference between <code>epptr()</code> and <code>pbase()</code>.
</p>
<p>
This value isn't meaningful unless the value of <code>epptr()</code>
can be precisely controlled by a program. That used to be possible
until we accepted the resolution of issue 432, but since then the
requirements on <code>overflow()</code> have been relaxed to allow it
to make more than 1 write position available (i.e., by setting
<code>epptr()</code> to some unspecified value past
<code>pptr()</code>). So after the first call to
<code>overflow()</code> positioning the output sequence relative to
end will have unspecified results.
</p>
<p>
In addition, in <code>in|out</code> mode, since <code>(egptr() ==
epptr())</code> need not hold, there are two different possible values
for <code>newoff</code>: <code>epptr() - pbase()</code> and
<code>egptr() - eback()</code>.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change the <code>newoff</code> column in the last row of Table 94 to
read:
</p>
<blockquote>
the <del>end</del> <ins>high mark</ins> pointer minus the beginning
pointer (<code><del>xend</del> <ins>high_mark</ins> - xbeg</code>).
</blockquote>
<hr>
<a name="564"><h3>564.&nbsp;stringbuf seekpos underspecified</h3></a><p><b>Section:</b>&nbsp;27.7.1.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.stringbuf.virtuals"> [lib.stringbuf.virtuals]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;23 Feb 2006</p>
<p>
The effects of the <code>seekpos()</code> member function of
<code>basic_stringbuf</code> simply say that the function positions
the input and/or output sequences but fail to spell out exactly
how. This is in contrast to the detail in which <code>seekoff()</code>
is described.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change 27.7.1.3, p13 to read:
</p>
<blockquote>
<p>
-13- <i>Effects:</i> <ins>Same as <tt>seekoff(off_type(<i>sp</i>), ios_base::beg,
<i>which</i>)</tt>.</ins> <del>Alters the stream position within the controlled sequences,
if possible, to correspond to the stream position stored in <tt><i>sp</i></tt>
(as described below).</del>
</p>
<ul>
<li><del>If <tt>(<i>which</i> &amp; ios_base::in) != 0</tt>, positions the input sequence.</del></li>
<li><del>If <tt>(<i>which</i> &amp; ios_base::out) != 0</tt>, positions the output sequence.</del></li>
<li><del>If <tt><i>sp</i></tt> is an invalid stream position, or if the function
positions neither sequence, the positioning operation fails. If <tt><i>sp</i></tt>
has not been obtained by a previous successful call to one of the positioning
functions (<tt>seekoff</tt>, <tt>seekpos</tt>, <tt>tellg</tt>, <tt>tellp</tt>)
the effect is undefined.</del></li>
</ul>
</blockquote>
<hr>
<a name="565"><h3>565.&nbsp;xsputn inefficient</h3></a><p><b>Section:</b>&nbsp;27.5.2.4.5 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.streambuf.virt.put"> [lib.streambuf.virt.put]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;23 Feb 2006</p>
<p>
<tt>streambuf::xsputn()</tt> is specified to have the effect of
"writing up to <tt>n</tt> characters to the output sequence as if by
repeated calls to <tt>sputc(c)</tt>."
</p>
<p>
Since <tt>sputc()</tt> is required to call <tt>overflow()</tt> when
<tt>(pptr() == epptr())</tt> is true, strictly speaking
<tt>xsputn()</tt> should do the same. However, doing so would be
suboptimal in some interesting cases, such as in unbuffered mode or
when the buffer is <tt>basic_stringbuf</tt>.
</p>
<p>
Assuming calling <tt>overflow()</tt> is not really intended to be
required and the wording is simply meant to describe the general
effect of appending to the end of the sequence it would be worthwhile
to mention in <tt>xsputn()</tt> that the function is not actually
required to cause a call to <tt>overflow()</tt>.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Add the following sentence to the <tt>xsputn()</tt> Effects clause in
27.5.2.4.5, p1 (N1804):
</p>
<blockquote>
<p>
-1- <i>Effects:</i> Writes up to <tt><i>n</i></tt> characters to the output
sequence as if by repeated calls to <tt>sputc(<i>c</i>)</tt>. The characters
written are obtained from successive elements of the array whose first element
is designated by <tt><i>s</i></tt>. Writing stops when either <tt><i>n</i></tt>
characters have been written or a call to <tt>sputc(<i>c</i>)</tt> would return
<tt>traits::eof()</tt>. <ins>It is uspecified whether the function calls
<tt>overflow()</tt> when <tt>(pptr() == epptr())</tt> becomes true or whether
it achieves the same effects by other means.</ins>
</p>
</blockquote>
<p>
In addition, I suggest to add a footnote to this function with the
same text as Footnote 292 to make it extra clear that derived classes
are permitted to override <tt>xsputn()</tt> for efficiency.
</p>
<hr>
<a name="566"><h3>566.&nbsp;array forms of unformatted input function undefined for zero-element arrays</h3></a><p><b>Section:</b>&nbsp;27.6.1.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.istream.unformatted"> [lib.istream.unformatted]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;23 Feb 2006</p>
<p>
The array forms of unformatted input functions don't have well-defined
semantics for zero-element arrays in a couple of cases. The affected
ones (<tt>istream::get()</tt> and <tt>getline()</tt>) are supposed to
terminate when <tt>(n - 1)</tt> characters are stored, which obviously
can never be true when <tt>(n == 0)</tt> to start with.
</p>
<p><b>Proposed resolution:</b></p>
<p>
I propose the following changes (references are relative to the
Working Draft (document N1804).
</p>
<p>
Change 27.6.1.3, p8 (<tt>istream::get()</tt>), bullet 1 as follows:
</p>
<blockquote>
<p>
<ins>if <tt>(n &lt; 1)</tt> is true or </ins> <tt>(n - 1)</tt>
characters are stored;
</p>
</blockquote>
<p>
Similarly, change 27.6.1.3, p18 (<tt>istream::getline()</tt>), bullet
3 as follows:
</p>
<blockquote>
<p>
<ins><tt>(n &lt; 1)</tt> is true or </ins><tt>(n - 1)</tt> characters
are stored (in which case the function calls
<tt>setstate(failbit)</tt>).
</p>
</blockquote>
<p>
Finally, change p21 as follows:
</p>
<blockquote>
<p>
In any case, <ins>provided <tt>(n &gt; 0)</tt> is true, </ins>it then
stores a null character (using charT()) into the next successive
location of the array.
</p>
</blockquote>
<hr>
<a name="567"><h3>567.&nbsp;streambuf inserter and extractor should be unformatted</h3></a><p><b>Section:</b>&nbsp;27.6 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.iostream.format"> [lib.iostream.format]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;25 Feb 2006</p>
<p>
Issue 60 explicitly made the extractor and inserter operators that
take a <tt>basic_streambuf*</tt> argument formatted input and output
functions, respectively. I believe that's wrong, certainly in the
case of the extractor, since formatted functions begin by extracting
and discarding whitespace. The extractor should not discard any
characters.
</p>
<p><b>Proposed resolution:</b></p>
<p>
I propose to change each operator to behave as unformatted input and
output function, respectively. The changes below are relative to the
working draft document number N1804.
</p>
<p>
Specifically, change 27.6.1.2.3, p14 as follows:
</p>
<p>
</p><blockquote>
<i>Effects</i>: Behaves as a<ins>n un</ins>formatted input function
(as described in <del>27.6.1.2.1</del><ins>27.6.1.3, paragraph
1</ins>).
</blockquote>
<p></p>
<p>
And change 27.6.2.5.3, p7 as follows:
</p>
<p>
</p><blockquote>
<i>Effects</i>: Behaves as a<ins>n un</ins>formatted output function
(as described in <del>27.6.2.5.1</del><ins>27.6.2.6, paragraph
1</ins>).
</blockquote>
<p></p>
<hr>
<a name="568"><h3>568.&nbsp;log2 overloads missing</h3></a><p><b>Section:</b>&nbsp;TR1 8.16.4 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.c99.cmath.over"> [tr.c99.cmath.over]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Paolo Carlini&nbsp; <b>Date:</b>&nbsp;7 Mar 2006</p>
<p>
<tt>log2</tt> is missing from the list of "additional overloads" in 8.16.4p1.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Add <tt>log2</tt> to the list of functions in 8.16.4p1.
</p>
<hr>
<a name="570"><h3>570.&nbsp;Request adding additional explicit specializations of char_traits</h3></a><p><b>Section:</b>&nbsp;21.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-strings.html#lib.char.traits"> [lib.char.traits]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Jack Reeves&nbsp; <b>Date:</b>&nbsp;6 Apr 2006</p>
<p>
Currently, the Standard Library specifies only a declaration for template class
char_traits&lt;&gt; and requires the implementation provide two explicit
specializations: char_traits&lt;char&gt; and char_traits&lt;wchar_t&gt;. I feel the Standard
should require explicit specializations for all built-in character types, i.e.
char, wchar_t, unsigned char, and signed char.
</p>
<p>
I have put together a paper (N1985) that describes this in more detail and
includes all the necessary wording.
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="571"><h3>571.&nbsp;Update C90 references to C99?</h3></a><p><b>Section:</b>&nbsp;1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/intro.html#intro.refs"> [intro.refs]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Beman Dawes&nbsp; <b>Date:</b>&nbsp;8 Apr 2006</p>
<p>
1.2 Normative references [intro.refs] of the WP currently refers to ISO/IEC
9899:1990, Programming languages - C. Should that be changed to ISO/IEC
9899:1999?
</p>
<p>
What impact does this have on the library?
</p>
<p><b>Proposed resolution:</b></p>
<p>
In 1.2/1 [intro.refs] of the WP, change:
</p>
<blockquote>
<ul>
<li>ISO/IEC 9899:<del>1990</del><ins>1999 + TC1 + TC2</ins>, <i>Programming languages - C</i>
</li>
</ul>
</blockquote>
<hr>
<a name="572"><h3>572.&nbsp;Oops, we gave 507 WP status</h3></a><p><b>Section:</b>&nbsp;TR1 5.1.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/tr1.html#tr.rand.var"> [tr.rand.var]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Howard Hinnant&nbsp; <b>Date:</b>&nbsp;11 Apr 2006</p>
<p>
In Berlin, as a working group, we voted in favor of N1932 which makes issue 507 moot:
variate_generator has been eliminated. Then in full committee we voted to give
this issue WP status (mistakenly).
</p>
<p><b>Proposed resolution:</b></p>
<p>
Strike the proposed resolution of issue 507.
</p>
<p><i>[
post-Portland: Howard recommends NAD. The proposed resolution of 507 no longer
exists in the current WD.
]</i></p>
<hr>
<a name="573"><h3>573.&nbsp;C++0x file positioning should handle modern file sizes</h3></a><p><b>Section:</b>&nbsp;27.4.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.fpos"> [lib.fpos]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Beman Dawes&nbsp; <b>Date:</b>&nbsp;12 Apr 2006</p>
<p>
There are two deficiencies related to file sizes:
</p>
<ol>
<li>It doesn't appear that the Standard Library is specified in
a way that handles modern file sizes, which are often too
large to be represented by an unsigned long.</li>
<li>The std::fpos class does not currently have the ability to
set/get file positions.</li>
</ol>
<p>
The Dinkumware implementation of the Standard Library as shipped with the Microsoft compiler copes with these issues by:
</p>
<ol type="A">
<li>Defining fpos_t be long long, which is large enough to
represent any file position likely in the foreseeable future.</li>
<li>Adding member functions to class fpos. For example,
<blockquote><pre>fpos_t seekpos() const;
</pre></blockquote>
</li>
</ol>
<p>
Because there are so many types relating to file positions and offsets (fpos_t,
fpos, pos_type, off_type, streamoff, streamsize, streampos, wstreampos, and
perhaps more), it is difficult to know if the Dinkumware extensions are
sufficient. But they seem a useful starting place for discussions, and they do
represent existing practice.
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="574"><h3>574.&nbsp;DR 369 Contradicts Text</h3></a><p><b>Section:</b>&nbsp;27.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.iostream.objects"> [lib.iostream.objects]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Pete Becker&nbsp; <b>Date:</b>&nbsp;18 Apr 2006</p>
<p>
lib.iostream.objects requires that the standard stream objects are never
destroyed, and it requires that they be destroyed.
</p>
<p>
DR 369 adds words to say that we really mean for ios_base::Init objects to force
construction of standard stream objects. It ends, though, with the phrase "these
stream objects shall be destroyed after the destruction of dynamically ...".
However, the rule for destruction is stated in the standard: "The objects are
not destroyed during program execution."
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="575"><h3>575.&nbsp;the specification of ~shared_ptr is MT-unfriendly, makes implementation assumptions</h3></a><p><b>Section:</b>&nbsp;20.6.6.2.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.util.smartptr.shared.dest"> [lib.util.smartptr.shared.dest]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Peter Dimov&nbsp; <b>Date:</b>&nbsp;23 Apr 2006</p>
<p>
[tr.util.smartptr.shared.dest] says in its second bullet:
</p>
<p>
"If *this shares ownership with another shared_ptr instance (use_count() &gt; 1),
decrements that instance's use count."
</p>
<p>
The problem with this formulation is that it presupposes the existence of an
"use count" variable that can be decremented and that is part of the state of a
shared_ptr instance (because of the "that instance's use count".)
</p>
<p>
This is contrary to the spirit of the rest of the specification that carefully
avoids to require an use count variable. Instead, use_count() is specified to
return a value, a number of instances.
</p>
<p>
In multithreaded code, the usual implicit assumption is that a shared variable
should not be accessed by more than one thread without explicit synchronization,
and by introducing the concept of an "use count" variable, the current wording
implies that two shared_ptr instances that share ownership cannot be destroyed
simultaneously.
</p>
<p>
In addition, if we allow the interpretation that an use count variable is part
of shared_ptr's state, this would lead to other undesirable consequences WRT
multiple threads. For example,
</p>
<blockquote><pre>p1 = p2;
</pre></blockquote>
<p>
would now visibly modify the state of p2, a "write" operation, requiring a lock.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change the first two bullets of [lib.util.smartptr.shared.dest]/1 to:
</p>
<blockquote><p>
</p><ul>
<li>If <tt>*this</tt> is <i>empty</i> <ins>or shares ownership with another
<tt>shared_ptr</tt> instance (<tt>use_count() &gt; 1</tt>)</ins>, there are no side effects.</li>
<li><del>If <tt>*this</tt> <i>shares ownership</i> with another <tt>shared_ptr</tt> instance
(<tt>use_count() &gt; 1</tt>), decrements that instance's use count.</del></li>
</ul>
<p></p></blockquote>
<p>
Add the following paragraph after [lib.util.smartptr.shared.dest]/1:
</p>
<blockquote><p>
[<i>Note:</i> since the destruction of <tt>*this</tt> decreases the number of instances in
<tt>*this</tt>'s ownership group by one, all <tt>shared_ptr</tt> instances that share ownership
with <tt>*this</tt> will report an <tt>use_count()</tt> that is one lower than its previous value
after <tt>*this</tt> is destroyed. <i>--end note</i>]
</p></blockquote>
<hr>
<a name="576"><h3>576.&nbsp;find_first_of is overconstrained</h3></a><p><b>Section:</b>&nbsp;25.1.4 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-algorithms.html#lib.alg.find.first.of"> [lib.alg.find.first.of]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Doug Gregor&nbsp; <b>Date:</b>&nbsp;25 Apr 2006</p>
<p>
In 25.1.4 Find First [lib.alg.find.first], the two iterator type parameters to
find_first_of are specified to require Forward Iterators, as follows:
</p>
<blockquote><pre>template&lt;class ForwardIterator1, class ForwardIterator2&gt;
ForwardIterator1
find_first_of(ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2);
template&lt;class ForwardIterator1, class ForwardIterator2,
class BinaryPredicate&gt;
ForwardIterator1
find_first_of(ForwardIterator1 first1, ForwardIterator1 last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred);
</pre></blockquote>
<p>
However, ForwardIterator1 need not actually be a Forward Iterator; an Input
Iterator suffices, because we do not need the multi-pass property of the Forward
Iterator or a true reference.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change the declarations of <tt>find_first_of</tt> to:
</p>
<blockquote><pre>template&lt;class <del>ForwardIterator1</del><ins>InputIterator1</ins>, class ForwardIterator2&gt;
<del>ForwardIterator1</del><ins>InputIterator1</ins>
find_first_of(<del>ForwardIterator1</del><ins>InputIterator1</ins> first1, <del>ForwardIterator1</del><ins>InputIterator1</ins> last1,
ForwardIterator2 first2, ForwardIterator2 last2);
template&lt;class <del>ForwardIterator1</del><ins>InputIterator1</ins>, class ForwardIterator2,
class BinaryPredicate&gt;
<del>ForwardIterator1</del><ins>InputIterator1</ins>
find_first_of(<del>ForwardIterator1</del><ins>InputIterator1</ins> first1, <del>ForwardIterator1</del><ins>InputIterator1</ins> last1,
ForwardIterator2 first2, ForwardIterator2 last2,
BinaryPredicate pred);
</pre></blockquote>
<hr>
<a name="577"><h3>577.&nbsp;upper_bound(first, last, ...) cannot return last</h3></a><p><b>Section:</b>&nbsp;25.3.3.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-algorithms.html#lib.upper.bound"> [lib.upper.bound]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Seungbeom Kim&nbsp; <b>Date:</b>&nbsp;3 May 2006</p>
<p>
ISO/IEC 14882:2003 says:
</p>
<blockquote>
<p>
25.3.3.2 upper_bound
</p>
<p>
<i>Returns:</i> The furthermost iterator <tt>i</tt> in the range
<tt>[<i>first</i>, <i>last</i>)</tt> such that
for any iterator <tt>j</tt> in the range <tt>[<i>first</i>, i)</tt> the following corresponding
conditions hold: <tt>!(value &lt; *j)</tt> or <tt><i>comp</i>(<i>value</i>, *j) == false</tt>.
</p>
</blockquote>
<p>
From the description above, upper_bound cannot return last, since it's
not in the interval [first, last). This seems to be a typo, because if
value is greater than or equal to any other values in the range, or if
the range is empty, returning last seems to be the intended behaviour.
The corresponding interval for lower_bound is also [first, last].
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change [lib.upper.bound]:
</p>
<blockquote>
<p>
<i>Returns:</i> The furthermost iterator <tt>i</tt> in the range
<tt>[<i>first</i>, <i>last</i><del>)</del><ins>]</ins></tt> such that
for any iterator <tt>j</tt> in the range <tt>[<i>first</i>, i)</tt> the following corresponding
conditions hold: <tt>!(value &lt; *j)</tt> or <tt><i>comp</i>(<i>value</i>, *j) == false</tt>.
</p>
</blockquote>
<hr>
<a name="578"><h3>578.&nbsp;purpose of hint to allocator::allocate()</h3></a><p><b>Section:</b>&nbsp;20.6.1.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.allocator.members"> [lib.allocator.members]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;17 May 2006</p>
<p>
The description of the allocator member function
<code>allocate()</code> requires that the <i>hint</i> argument be
either 0 or a value previously returned from <code>allocate()</code>.
Footnote 227 further suggests that containers may pass the address of
an adjacent element as this argument.
</p>
<p>
I believe that either the footnote is wrong or the normative
requirement that the argument be a value previously returned from a
call to <code>allocate()</code> is wrong. The latter is supported by
the resolution to issue 20-004 proposed in c++std-lib-3736 by Nathan
Myers. In addition, the <i>hint</i> is an ordinary void* and not the
<code>pointer</code> type returned by <code>allocate()</code>, with
the two types potentially being incompatible and the requirement
impossible to satisfy.
</p>
<p>
See also c++std-lib-14323 for some more context on where this came up
(again).
</p>
<p><b>Proposed resolution:</b></p>
<p>
Remove the requirement in 20.6.1.1, p4 that the hint be a value
previously returned from <code>allocate()</code>. Specifically, change
the paragraph as follows:
</p>
<p>
<i>Requires</i>: <i>hint</i> <ins>is </ins>either 0 or <del>previously
obtained from member <code>allocate</code> and not yet passed to
member <code>deallocate</code></del><ins> the address of a byte in
memory (1.7)</ins>.
</p>
<hr>
<a name="579"><h3>579.&nbsp;erase(iterator) for unordered containers should not return an iterator</h3></a><p><b>Section:</b>&nbsp;23.1.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.unord.req"> [lib.unord.req]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Joaqu<EFBFBD>n M L<>pez Mu<4D>oz&nbsp; <b>Date:</b>&nbsp;13 Jun 2006</p>
<p>
See
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2023.pdf">N2023</a>
for full discussion.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Option 1:
</p>
<p>
The problem can be eliminated by omitting the requirement that <tt>a.erase(q)</tt> return an
iterator. This is, however, in contrast with the equivalent requirements for other
standard containers.
</p>
<p>
Option 2:
</p>
<p>
<tt>a.erase(q)</tt> can be made to compute the next iterator only when explicitly requested:
the technique consists in returning a proxy object implicitly convertible to <tt>iterator</tt>, so
that
</p>
<blockquote><pre>iterator q1=a.erase(q);
</pre></blockquote>
<p>
works as expected, while
</p>
<blockquote><pre>a.erase(q);
</pre></blockquote>
<p>
does not ever invoke the conversion-to-iterator operator, thus avoiding the associated
computation. To allow this technique, some sections of TR1 along the line "return value
is an iterator..." should be changed to "return value is an unspecified object implicitly
convertible to an iterator..." Although this trick is expected to work transparently, it can
have some collateral effects when the expression <tt>a.erase(q)</tt> is used inside generic
code.
</p>
<hr>
<a name="580"><h3>580.&nbsp;unused allocator members</h3></a><p><b>Section:</b>&nbsp;20.1.6 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.allocator.requirements"> [lib.allocator.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;14 June 2006</p>
<p>
C++ Standard Library templates that take an allocator as an argument
are required to call the <code>allocate()</code> and
<code>deallocate()</code> members of the allocator object to obtain
storage. However, they do not appear to be required to call any other
allocator members such as <code>construct()</code>,
<code>destroy()</code>, <code>address()</code>, and
<code>max_size()</code>. This makes these allocator members less than
useful in portable programs.
</p>
<p><b>Proposed resolution:</b></p>
<p>
It's unclear to me whether the absence of the requirement to use these
allocator members is an unintentional omission or a deliberate
choice. However, since the functions exist in the standard allocator
and since they are required to be provided by any user-defined
allocator I believe the standard ought to be clarified to explictly
specify whether programs should or should not be able to rely on
standard containers calling the functions.
</p>
<p>
I propose that all containers be required to make use of these
functions.
</p>
<hr>
<a name="581"><h3>581.&nbsp;<code>flush()</code> not unformatted function</h3></a><p><b>Section:</b>&nbsp;27.6.2.6 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.ostream.unformatted"> [lib.ostream.unformatted]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;14 June 2006</p>
<p>
The resolution of issue 60 changed <code>basic_ostream::flush()</code>
so as not to require it to behave as an unformatted output function.
That has at least two in my opinion problematic consequences:
</p>
<p>
First, <code>flush()</code> now calls <code>rdbuf()-&gt;pubsync()</code>
unconditionally, without regard to the state of the stream. I can't
think of any reason why <code>flush()</code> should behave differently
from the vast majority of stream functions in this respect.
</p>
<p>
Second, <code>flush()</code> is not required to catch exceptions from
<code>pubsync()</code> or set <code>badbit</code> in response to such
events. That doesn't seem right either, as most other stream functions
do so.
</p>
<p><b>Proposed resolution:</b></p>
<p>
I propose to revert the resolution of issue 60 with respect to
<code>flush()</code>. Specifically, I propose to change 27.6.2.6, p7
as follows:
</p>
Effects: <ins>Behaves as an unformatted output function (as described
in 27.6.2.6, paragraph 1). </ins>If <code>rdbuf()</code> is not a null
pointer, <ins>constructs a sentry object. If this object returns
<code>true</code> when converted to a value of type bool the function
</ins>calls <code>rdbuf()-&gt;pubsync()</code>. If that function returns
-1 calls <code>setstate(badbit)</code> (which may throw
<code>ios_base::failure</code> (27.4.4.3)). <ins>Otherwise, if the
sentry object returns <code>false</code>, does nothing.</ins><del>Does
not behave as an unformatted output function (as described in
27.6.2.6, paragraph 1).</del>
<hr>
<a name="582"><h3>582.&nbsp;specialized algorithms and volatile storage</h3></a><p><b>Section:</b>&nbsp;20.6.4.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.uninitialized.copy"> [lib.uninitialized.copy]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;14 June 2006</p>
<p>
The specialized algorithms [lib.specialized.algorithms] are specified
as having the general effect of invoking the following expression:
</p>
<p>
</p><pre>
new (static_cast&lt;void*&gt;(&amp;*i))
typename iterator_traits&lt;ForwardIterator&gt;::value_type (x)
</pre>
<p></p>
<p>
This expression is ill-formed when the type of the subexpression
<code>&amp;*i</code> is some volatile-qualified <code>T</code>.
</p>
<p><b>Proposed resolution:</b></p>
<p>
In order to allow these algorithms to operate on volatile storage I
propose to change the expression so as to make it well-formed even for
pointers to volatile types. Specifically, I propose the following
changes to clauses 20 and 24. Change 20.6.4.1, p1 to read:
</p>
<p>
</p><pre>
<i>Effects</i>:
typedef typename iterator_traits&lt;ForwardIterator&gt;::pointer pointer;
typedef typename iterator_traits&lt;ForwardIterator&gt;::value_type value_type;
for (; first != last; ++result, ++first)
new (static_cast&lt;void*&gt;(const_cast&lt;pointer&gt;(&amp;*result))
value_type (*first);
</pre>
<p></p>
<p>
change 20.6.4.2, p1 to read
</p>
<p>
</p><pre>
<i>Effects</i>:
typedef typename iterator_traits&lt;ForwardIterator&gt;::pointer pointer;
typedef typename iterator_traits&lt;ForwardIterator&gt;::value_type value_type;
for (; first != last; ++result, ++first)
new (static_cast&lt;void*&gt;(const_cast&lt;pointer&gt;(&amp;*first))
value_type (*x);
</pre>
<p></p>
<p>
and change 20.6.4.3, p1 to read
</p>
<p>
</p><pre>
<i>Effects</i>:
typedef typename iterator_traits&lt;ForwardIterator&gt;::pointer pointer;
typedef typename iterator_traits&lt;ForwardIterator&gt;::value_type value_type;
for (; n--; ++first)
new (static_cast&lt;void*&gt;(const_cast&lt;pointer&gt;(&amp;*first))
value_type (*x);
</pre>
<p></p>
<p>
In addition, since there is no partial specialization for
<code>iterator_traits&lt;volatile T*&gt;</code> I propose to add one
to parallel such specialization for &lt;const T*&gt;. Specifically, I
propose to add the following text to the end of 24.3.1, p3:
</p>
<p>
and for pointers to volatile as
</p>
<p>
</p><pre>
namespace std {
template&lt;class T&gt; struct iterator_traits&lt;volatile T*&gt; {
typedef ptrdiff_t difference_type;
typedef T value_type;
typedef volatile T* pointer;
typedef volatile T&amp; reference;
typedef random_access_iterator_tag iterator_category;
};
}
</pre>
<p></p>
<p>
Note that the change to <code>iterator_traits</code> isn't necessary
in order to implement the specialized algorithms in a way that allows
them to operate on volatile strorage. It is only necesassary in order
to specify their effects in terms of <code>iterator_traits</code> as
is done here. Implementations can (and some do) achieve the same
effect by means of function template overloading.
</p>
<hr>
<a name="583"><h3>583.&nbsp;div() for unsigned integral types</h3></a><p><b>Section:</b>&nbsp;26.7 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.c.math"> [lib.c.math]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Beman Dawes&nbsp; <b>Date:</b>&nbsp;15 Jun 2006</p>
<p>
There is no div() function for unsigned integer types.
</p>
<p>
There are several possible resolutions. The simplest one is noted below. Other
possibilities include a templated solution.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Add to 26.7 [lib.c.math] paragraph 8:
</p>
<blockquote><pre>struct udiv_t div(unsigned, unsigned);
struct uldiv_t div(unsigned long, unsigned long);
struct ulldiv_t div(unsigned long long, unsigned long long);
</pre></blockquote>
<hr>
<a name="584"><h3>584.&nbsp;missing int pow(int,int) functionality</h3></a><p><b>Section:</b>&nbsp;26.7 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.c.math"> [lib.c.math]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Beman Dawes&nbsp; <b>Date:</b>&nbsp;15 Jun 2006</p>
<p>
There is no pow() function for any integral type.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Add something like:
</p>
<blockquote><pre>template&lt; typename T&gt;
T power( T x, int n );
// requires: n &gt;=0
</pre></blockquote>
<hr>
<a name="585"><h3>585.&nbsp;facet error reporting</h3></a><p><b>Section:</b>&nbsp;22.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-locales.html#lib.locale.categories"> [lib.locale.categories]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor, Paolo Carlini&nbsp; <b>Date:</b>&nbsp;22 June 2006</p>
<p>
Section 22.2, paragraph 2 requires facet <code>get()</code> members
that take an <code>ios_base::iostate&amp;</code> argument,
<code><i>err</i></code>, to ignore the (initial) value of the
argument, but to set it to <code>ios_base::failbit</code> in case of a
parse error.
</p>
<p>
We believe there are a few minor problems with this blanket
requirement in conjunction with the wording specific to each
<code>get()</code> member function.
</p>
<p>
First, besides <code>get()</code> there are other member functions
with a slightly different name (for example,
<code>get_date()</code>). It's not completely clear that the intent of
the paragraph is to include those as well, and at least one
implementation has interpreted the requirement literally.
</p>
<p>
Second, the requirement to "set the argument to
<code>ios_base::failbit</code> suggests that the functions are not
permitted to set it to any other value (such as
<code>ios_base::eofbit</code>, or even <code>ios_base::eofbit |
ios_base::failbit</code>).
</p>
<p>
However, 22.2.2.1.2, p5 (Stage 3 of <code>num_get</code> parsing) and
p6 (<code>bool</code> parsing) specifies that the <code>do_get</code>
functions perform <code><i>err</i> |= ios_base::eofbit</code>, which
contradicts the earlier requirement to ignore <i>err</i>'s initial
value.
</p>
<p>
22.2.6.1.2, p1 (the Effects clause of the <code>money_get</code>
facet's <code>do_get</code> member functions) also specifies that
<code><i>err</i></code>'s initial value be used to compute the final
value by ORing it with either <code>ios_base::failbit</code> or
with<code>ios_base::eofbit | ios_base::failbit</code>.
</p>
<p><b>Proposed resolution:</b></p>
<p>
We believe the intent is for all facet member functions that take an
<code>ios_base::iostate&amp;</code> argument to:
</p>
<p>
</p><ul>
<li>
ignore the initial value of the <code><i>err</i></code> argument,
</li>
<li>
reset <code><i>err</i></code> to <code>ios_base::goodbit</code> prior
to any further processing,
</li>
<li>
and set either <code>ios_base::eofbit</code>, or
<code>ios_base::failbit</code>, or both in <code><i>err</i></code>, as
appropriate, in response to reaching the end-of-file or on parse
error, or both.
</li>
</ul>
<p></p>
<p>
To that effect we propose to change 22.2, p2 as follows:
</p>
<p>
The <i>put</i><del>()</del> members make no provision for error
reporting. (Any failures of the OutputIterator argument must be
extracted from the returned iterator.) <ins>Unless otherwise
specified, </ins>the <i>get</i><del>()</del> members <ins>that</ins>
take an <code>ios_base::iostate&amp;</code> argument <del>whose value
they ignore, but set to ios_base::failbit in case of a parse
error.</del><ins>, <code><i>err</i></code>, start by evaluating
<code>err = ios_base::goodbit</code>, and may subsequently set
<i>err</i> to either <code>ios_base::eofbit</code>, or
<code>ios_base::failbit</code>, or <code>ios_base::eofbit |
ios_base::failbit</code> in response to reaching the end-of-file or in
case of a parse error, or both, respectively.</ins>
</p>
<hr>
<a name="586"><h3>586.&nbsp;string inserter not a formatted function</h3></a><p><b>Section:</b>&nbsp;21.3.7.9 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-strings.html#lib.string.io"> [lib.string.io]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;22 June 2006</p>
<p>
Section and paragraph numbers in this paper are relative to the
working draft document number N2009 from 4/21/2006.
</p>
<p>
The <code>basic_string</code> extractor in 21.3.7.9, p1 is clearly
required to behave as a formatted input function, as is the
<code>std::getline()</code> overload for string described in p7.
</p>
<p>
However, the <code>basic_string</code> inserter described in p5 of the
same section has no such requirement. This has implications on how the
operator responds to exceptions thrown from <code>xsputn()</code>
(formatted output functions are required to set <code>badbit</code>
and swallow the exception unless <code>badbit</code> is also set in
<code>exceptions()</code>; the string inserter doesn't have any such
requirement).
</p>
<p>
I don't see anything in the spec for the string inserter that would
justify requiring it to treat exceptions differently from all other
similar operators. (If it did, I think it should be made this explicit
by saying that the operator "does not behave as a formatted output
function" as has been made customary by the adoption of the resolution
of issue 60).
</p>
<p><b>Proposed resolution:</b></p>
<p>
I propose to change the Effects clause in 21.3.7.9, p5, as follows:
</p>
<p>
</p><blockquote>
<i>Effects</i>: <del>Begins by constructing a sentry object k as if k
were constructed by typename <code>basic_ostream&lt;charT,
traits&gt;::sentry k (os)</code>. If <code>bool(k)</code> is
<code>true</code>, </del><ins>Behaves as a formatted output function
(27.6.2.5.1). After constructing a <code>sentry</code> object, if
this object returns <code>true</code> when converted to a value of
type <code>bool</code>, determines padding as described in
22.2.2.2.2</ins>, then inserts the resulting sequence of characters
<code><i>seq</i></code> as if by calling <code>os.rdbuf()-&gt;sputn(seq ,
n)</code>, where <code><i>n</i></code> is the larger of
<code>os.width()</code> and <code>str.size()</code>; then calls
<code>os.width(0)</code>. <del>If the call to sputn fails, calls
<code>os.setstate(ios_base::failbit)</code>.</del>
</blockquote>
<p></p>
<p>
This proposed resilution assumes the resolution of issue 394 (i.e.,
that all formatted output functions are required to set
<code>ios_base::badbit</code> in response to any kind of streambuf
failure), and implicitly assumes that a return value of
<code>sputn(seq, <i>n</i>)</code> other than <code><i>n</i></code>
indicates a failure.
</p>
<hr>
<a name="587"><h3>587.&nbsp;iststream ctor missing description</h3></a><p><b>Section:</b>&nbsp;D.7.2.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/future.html#depr.istrstream.cons"> [depr.istrstream.cons]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;22 June 2006</p>
<p>
The <code>iststream(char*, streamsize)</code> ctor is in the class
synopsis in D.7.2 but its signature is missing in the description
below (in D.7.2.1).
</p>
<p><b>Proposed resolution:</b></p>
<p>
This seems like a simple editorial issue and the missing signature can
be added to the one for <code>const char*</code> in paragraph 2.
</p>
<hr>
<a name="588"><h3>588.&nbsp;requirements on zero sized tr1::arrays and other details</h3></a><p><b>Section:</b>&nbsp;23.2.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.array"> [lib.array]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Gennaro Prota&nbsp; <b>Date:</b>&nbsp;18 Jul 2006</p>
<p>
The wording used for section 23.2.1 [lib.array] seems to be subtly
ambiguous about zero sized arrays (N==0). Specifically:
</p>
<p>
* "An instance of array&lt;T, N&gt; stores N elements of type T, so that
[...]"
</p>
<p>
Does this imply that a zero sized array object stores 0 elements, i.e.
that it cannot store any element of type T? The next point clarifies
the rationale behind this question, basically how to implement begin()
and end():
</p>
<p>
* 23.2.1.5 [lib.array.zero], p2: "In the case that N == 0, begin() ==
end() == unique value."
</p>
<p>
What does "unique" mean in this context? Let's consider the following
possible implementations, all relying on a partial specialization:
</p>
<blockquote><pre>a)
template&lt; typename T &gt;
class array&lt; T, 0 &gt; {
....
iterator begin()
{ return iterator( reinterpret_cast&lt; T * &gt;( this ) ); }
....
};
</pre></blockquote>
<p>
This has been used in boost, probably intending that the return value
had to be unique to the specific array object and that array couldn't
store any T. Note that, besides relying on a reinterpret_cast, has
(more than potential) alignment problems.
</p>
<blockquote><pre>b)
template&lt; typename T &gt;
class array&lt; T, 0 &gt; {
T t;
iterator begin()
{ return iterator( &amp;t ); }
....
};
</pre></blockquote>
<p>
This provides a value which is unique to the object and to the type of
the array, but requires storing a T. Also, it would allow the user to
mistakenly provide an initializer list with one element.
</p>
<p>
A slight variant could be returning *the* null pointer of type T
</p>
<blockquote><pre> return static_cast&lt;T*&gt;(0);
</pre></blockquote>
<p>
In this case the value would be unique to the type array&lt;T, 0&gt; but not
to the objects (all objects of type array&lt;T, 0&gt; with the same value
for T would yield the same pointer value).
</p>
<p>
Furthermore this is inconsistent with what the standard requires from
allocation functions (see library issue 9).
</p>
<p>
c) same as above but with t being a static data member; again, the
value would be unique to the type, not to the object.
</p>
<p>
d) to avoid storing a T *directly* while disallowing the possibility
to use a one-element initializer list a non-aggregate nested class
could be defined
</p>
<blockquote><pre> struct holder { holder() {} T t; } h;
</pre></blockquote>
<p>
and then begin be defined as
</p>
<blockquote><pre> iterator begin() { return &amp;h.t; }
</pre></blockquote>
<p>
But then, it's arguable whether the array stores a T or not.
Indirectly it does.
</p>
<p>
-----------------------------------------------------
</p>
<p>
Now, on different issues:
</p>
<p>
* what's the effect of calling assign(T&amp;) on a zero-sized array? There
seems to be only mention of front() and back(), in 23.2.1 [lib.array]
p4 (I would also suggest to move that bullet to section 23.2.1.5
[lib.array.zero], for locality of reference)
</p>
<p>
* (minor) the opening paragraph of 23.2.1 [lib.array] wording is a bit
inconsistent with that of other sequences: that's not a problem in
itself, but compare it for instance with "A vector is a kind of
sequence that supports random access iterators"; though the intent is
obvious one might argue that the wording used for arrays doesn't tell
what an array is, and relies on the reader to infer that it is what
the &lt;array&gt; header defines.
</p>
<p>
* it would be desiderable to have a static const data member of type
std::size_t, with value N, for usage as integral constant expression
</p>
<p>
* section 23.1 [lib.container.requirements] seem not to consider
fixed-size containers at all, as it says: "[containers] control
allocation and deallocation of these objects [the contained objects]
through constructors, destructors, *insert and erase* operations"
</p>
<p>
* max_size() isn't specified: the result is obvious but, technically,
it relies on table 80: "size() of the largest possible container"
which, again, doesn't seem to consider fixed size containers
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p>
<hr>
<a name="589"><h3>589.&nbsp;Requirements on iterators of member template functions of containers</h3></a><p><b>Section:</b>&nbsp;23.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-containers.html#lib.container.requirements"> [lib.container.requirements]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Peter Dimov&nbsp; <b>Date:</b>&nbsp;2 Aug 2006</p>
<p>
There appears to be no requirements on the InputIterators used in sequences in 23.1.1 in
terms of their value_type, and the requirements in 23.1.2 appear to be overly strict
(requires InputIterator::value_type be the same type as the container's value_type).
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change 23.1.1 p3:
</p>
<blockquote>
In Tables 82 and 83, <tt>X</tt> denotes a sequence class, <tt>a</tt> denotes a
value of <tt>X</tt>, <tt>i</tt> and <tt>j</tt> denote iterators satisfying input
iterator requirements <ins>and refer to elements <ins>implicitly
convertible to</ins> <tt>value_type</tt></ins>, <tt>[i, j)</tt> denotes a valid
range, <tt>n</tt> denotes a value of <tt>X::size_type</tt>, <tt>p</tt> denotes a
valid iterator to <tt>a</tt>, <tt>q</tt> denotes a valid dereferenceable
iterator to <tt>a</tt>, <tt>[q1, q2)</tt> denotes a valid range in <tt>a</tt>,
and <tt>t</tt> denotes a value of <tt>X::value_type</tt>.
</blockquote>
<p>
Change 23.1.2 p7:
</p>
<blockquote>
In Table 84, <tt>X</tt> is an associative container class, <tt>a</tt> is a value
of <tt>X</tt>, <tt>a_uniq</tt> is a value of <tt>X</tt> when <tt>X</tt> supports
unique keys, and <tt>a_eq</tt> is a value of <tt>X</tt> when <tt>X</tt> supports
multiple keys, <tt>i</tt> and <tt>j</tt> satisfy input iterator requirements and
refer to elements <del>of</del> <ins>implicitly convertible to</ins>
<tt>value_type</tt>, <tt>[i, j)</tt> is a valid range, <tt>p</tt> is a valid
iterator to <tt>a</tt>, <tt>q</tt> is a valid dereferenceable iterator to
<tt>a</tt>, <tt>[q1, q2)</tt> is a valid range in <tt>a</tt>, <tt>t</tt> is a
value of <tt>X::value_type</tt>, <tt>k</tt> is a value of <tt>X::key_type</tt>
and <tt>c</tt> is a value of type <tt>X::key_compare</tt>.
</blockquote>
<hr>
<a name="590"><h3>590.&nbsp;Type traits implementation latitude should be removed for C++0x</h3></a><p><b>Section:</b>&nbsp;<font color="red">20.4.9</font>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Beman Dawes&nbsp; <b>Date:</b>&nbsp;10 Aug 2006</p>
<p>
20.4.9 [lib.meta.req], Implementation requirements, provides latitude for type
traits implementers that is not needed in C++0x. It includes the wording:
</p>
<blockquote>
[<i>Note:</i> the latitude granted to implementers in this clause is temporary,
and is expected to be removed in future revisions of this document. -- <i>end note</i>]
</blockquote>
<p>
Note:
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2028.html">N2028:
Minor Modifications to the type traits Wording</a>
also has the intent of removing this wording from the WP.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Remove 20.4.9 [lib.meta.req] in its entirety from the WP.
</p>
<hr>
<a name="591"><h3>591.&nbsp;Misleading "built-in</h3></a><p><b>Section:</b>&nbsp;18.2.1.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-support.html#lib.numeric.limits.members"> [lib.numeric.limits.members]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;whyglinux&nbsp; <b>Date:</b>&nbsp;8 Aug 2006</p>
<p>
18.2.1.2 numeric_limits members [lib.numeric.limits.members]
Paragraph 7:
</p>
<blockquote>
"For built-in integer types, the number of non-sign bits in the
representation."
</blockquote>
<p>
26.1 Numeric type requirements [lib.numeric.requirements]
Footnote:
</p>
<blockquote>
"In other words, value types. These include built-in arithmetic types,
pointers, the library class complex, and instantiations of valarray for
value types."
</blockquote>
<p>
Integer types (which are bool, char, wchar_t, and the signed and
unsigned integer types) and arithmetic types (which are integer and
floating types) are all built-in types and thus there are no
non-built-in (that is, user-defined) integer or arithmetic types. Since
the redundant "built-in" in the above 2 sentences can mislead that
there may be built-in or user-defined integer and arithmetic types
(which is not correct), the "built-in" should be removed.
</p>
<p><b>Proposed resolution:</b></p>
<p>
</p><p>
18.2.1.2 numeric_limits members [lib.numeric.limits.members]
Paragraph 7:
</p>
<blockquote>
"For <del>built-in</del> integer types, the number of non-sign bits in the
representation."
</blockquote>
<p>
26.1 Numeric type requirements [lib.numeric.requirements]
Footnote:
</p>
<blockquote>
"In other words, value types. These include <del>built-in</del> arithmetic types,
pointers, the library class complex, and instantiations of valarray for
value types."
</blockquote>
<p></p>
<hr>
<a name="592"><h3>592.&nbsp;Incorrect treatment of rdbuf()-&gt;close() return type</h3></a><p><b>Section:</b>&nbsp;27.8.1.7 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.ifstream.members"> [lib.ifstream.members]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Christopher Kohlhoff&nbsp; <b>Date:</b>&nbsp;17 Aug 2006</p>
<p>
I just spotted a minor problem in 27.8.1.7
[lib.ifstream.members] para 4 and also 27.8.1.13
[lib.fstream.members] para 4. In both places it says:
</p>
<blockquote>
<pre>void close();
</pre>
<p>
Effects: Calls rdbuf()-&gt;close() and, if that function returns false, ...
</p>
</blockquote>
<p>
However, basic_filebuf::close() (27.8.1.2) returns a pointer to the
filebuf on success, null on failure, so I think it is meant to
say "if that function returns a null pointer". Oddly, it is
correct for basic_ofstream.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change 27.8.1.7 [lib.ifstream.members], p5:
</p>
<blockquote>
<i>Effects:</i> Calls <tt>rdbuf()-&gt;close()</tt> and, if that function
<ins>fails (</ins>returns <del><tt>false</tt></del> <ins>a null pointer)</ins>,
calls <tt>setstate(failbit)</tt> (which may throw <tt>ios_base::failure</tt>
(27.4.4.3)).
</blockquote>
<p>
Change 27.8.1.13 [lib.fstream.members], p5:
</p>
<blockquote>
<i>Effects:</i> Calls <tt>rdbuf()-&gt;close()</tt> and, if that function
<ins>fails (</ins>returns <del><tt>false</tt></del> <ins>a null pointer)</ins>,
calls <tt>setstate(failbit)</tt> (which may throw <tt>ios_base::failure</tt>
(27.4.4.3)).
</blockquote>
<hr>
<a name="593"><h3>593.&nbsp;__STDC_CONSTANT_MACROS</h3></a><p><b>Section:</b>&nbsp;18.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-support.html#lib.cstdint"> [lib.cstdint]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Walter Brown&nbsp; <b>Date:</b>&nbsp;28 Aug 2006</p>
<p>
Clause 18.3 of the current Working Paper (N2009) deals with the new C++ headers
&lt;cstdint&gt; and &lt;stdint.h&gt;. These are of course based on the C99 header
&lt;stdint.h&gt;, and were part of TR1.
</p>
<p>
Per 18.3.1/1, these headers define a number of macros and function macros.
While the WP does not mention __STDC_CONSTANT_MACROS in this context, C99
footnotes do mention __STDC_CONSTANT_MACROS. Further, 18.3.1/2 states that "The
header defines all ... macros the same as C99 subclause 7.18."
</p>
<p>
Therefore, if I wish to have the above-referenced macros and function macros
defined, must I #define __STDC_CONSTANT_MACROS before I #include &lt;cstdint&gt;, or
does the C++ header define these macros/function macros unconditionally?
</p>
<p><b>Proposed resolution:</b></p>
<p>
To put this issue to rest for C++0X, I propose the following addition to
18.3.1/2 of the Working Paper N2009:
</p>
<blockquote>
[Note: The macros defined by &lt;cstdint&gt; are provided unconditionally: in
particular, the symbols __STDC_LIMIT_MACROS and __STDC_CONSTANT_MACROS
(mentioned in C99 footnotes 219, 220, and 222) play no role in C++. --end note]
</blockquote>
<hr>
<a name="594"><h3>594.&nbsp;Disadvantages of defining Swappable in terms of
CopyConstructible and Assignable</h3></a><p><b>Section:</b>&nbsp;20.1.4 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-utilities.html#lib.swappable"> [lib.swappable]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Niels Dekker&nbsp; <b>Date:</b>&nbsp;2 Nov 2006</p>
<p>
It seems undesirable to define the Swappable requirement in terms of
CopyConstructible and Assignable requirements. And likewise, once the
MoveConstructible and MoveAssignable requirements (N1860) have made it
into the Working Draft, it seems undesirable to define the Swappable
requirement in terms of those requirements. Instead, it appears
preferable to have the Swappable requirement defined exclusively in
terms of the existence of an appropriate swap function.
</p>
<p>
Section 20.1.4 [lib.swappable] of the current Working Draft (N2009)
says:
</p><blockquote>
The Swappable requirement is met by satisfying one or more of the
following conditions:
<ul>
<li>
T is Swappable if T satisfies the CopyConstructible requirements
(20.1.3) and the Assignable requirements (23.1);
</li>
<li>
T is Swappable if a namespace scope function named swap exists in the
same namespace as the definition of T, such that the expression
swap(t,u) is valid and has the semantics described in Table 33.
</li>
</ul>
</blockquote>
I can think of three disadvantages of this definition:
<ol>
<li>
If a client's type T satisfies the first condition (T is both
CopyConstructible and Assignable), the client cannot stop T from
satisfying the Swappable requirement without stopping T from
satisfying the first condition.
<p>
A client might want to stop T from satisfying the Swappable
requirement, because swapping by means of copy construction and
assignment might throw an exception, and she might find a throwing
swap unacceptable for her type. On the other hand, she might not feel
the need to fully implement her own swap function for this type. In
this case she would want to be able to simply prevent algorithms that
would swap objects of type T from being used, e.g., by declaring a
swap function for T, and leaving this function purposely undefined.
This would trigger a link error, if an attempt would be made to use
such an algorithm for this type. For most standard library
implementations, this practice would indeed have the effect of
stopping T from satisfying the Swappable requirement.
</p>
</li>
<li>
A client's type T that does not satisfy the first condition can not be
made Swappable by providing a specialization of std::swap for T.
<p>
While I'm aware about the fact that people have mixed feelings about
providing a specialization of std::swap, it is well-defined to do so.
It sounds rather counter-intuitive to say that T is not Swappable, if
it has a valid and semantically correct specialization of std::swap.
Also in practice, providing such a specialization will have the same
effect as satisfying the Swappable requirement.
</p>
</li>
<li>
For a client's type T that satisfies both conditions of the Swappable
requirement, it is not specified which of the two conditions prevails.
After reading section 20.1.4 [lib.swappable], one might wonder whether
objects of T will be swapped by doing copy construction and
assignments, or by calling the swap function of T.
<p>
I'm aware that the intention of the Draft is to prefer calling the
swap function of T over doing copy construction and assignments. Still
in my opinion, it would be better to make this clear in the wording of
the definition of Swappable.
</p>
</li>
</ol>
<p></p>
<p>
I would like to have the Swappable requirement defined in such a way
that the following code fragment will correctly swap two objects of a
type T, if and only if T is Swappable:
</p><pre> using std::swap;
swap(t, u); // t and u are of type T.
</pre>
This is also the way Scott Meyers recommends calling a swap function,
in Effective C++, Third Edition, item 25.
<p></p>
<p>
Most aspects of this issue have been dealt with in a discussion on
comp.std.c++ about the Swappable requirement, from 13 September to 4
October 2006, including valuable input by David Abrahams, Pete Becker,
Greg Herlihy, Howard Hinnant and others.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change section 20.1.4 [lib.swappable] as follows:
</p>
<blockquote>
The Swappable requirement is met by satisfying
<del>one or more of the following conditions:</del>
<ins>the following condition:</ins>
<ul>
<del>
<li>
T is Swappable if T satisfies the CopyConstructible requirements
(20.1.3) and the Assignable requirements (23.1);
</li>
</del>
<li>
<del>
T is Swappable if a namespace scope function named swap exists in the
same namespace as the definition of T, such that the expression
swap(t,u) is valid and has the semantics described in Table 33.
</del>
T is Swappable if an unqualified function call swap(t,u) is valid
within the namespace std, and has the semantics described in Table 33.
</li>
</ul>
</blockquote>
<hr>
<a name="595"><h3>595.&nbsp;TR1/C++0x: fabs(complex&lt;T&gt;) redundant / wrongly specified</h3></a><p><b>Section:</b>&nbsp;26.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.complex.numbers"> [lib.complex.numbers]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Stefan Gro<72>e Pawig&nbsp; <b>Date:</b>&nbsp;24 Sep 2006</p>
<p>
TR1 introduced, in the C compatibility chapter, the function
fabs(complex&lt;T&gt;):
</p>
<blockquote><pre>----- SNIP -----
8.1.1 Synopsis [tr.c99.cmplx.syn]
namespace std {
namespace tr1 {
[...]
template&lt;class T&gt; complex&lt;T&gt; fabs(const complex&lt;T&gt;&amp; x);
} // namespace tr1
} // namespace std
[...]
8.1.8 Function fabs [tr.c99.cmplx.fabs]
1 Effects: Behaves the same as C99 function cabs, defined in
subclause 7.3.8.1.
----- SNIP -----
</pre></blockquote>
<p>
The current C++0X draft document (n2009.pdf) adopted this
definition in chapter 26.3.1 (under the comment // 26.3.7 values)
and 26.3.7/7.
</p>
<p>
But in C99 (ISO/IEC 9899:1999 as well as the 9899:TC2 draft document
n1124), the referenced subclause reads
</p>
<blockquote><pre>----- SNIP -----
7.3.8.1 The cabs functions
Synopsis
1 #include &lt;complex.h&gt;
double cabs(double complex z);
float cabsf(float complex z);
long double cabsl(long double z);
Description
2 The cabs functions compute the complex absolute value (also called
norm, modulus, or magnitude) of z.
Returns
3 The cabs functions return the complex absolute value.
----- SNIP -----
</pre></blockquote>
<p>
Note that the return type of the cabs*() functions is not a complex
type. Thus, they are equivalent to the already well established
template&lt;class T&gt; T abs(const complex&lt;T&gt;&amp; x);
(26.2.7/2 in ISO/IEC 14882:1998, 26.3.7/2 in the current draft
document n2009.pdf).
</p>
<p>
So either the return value of fabs() is specified wrongly, or fabs()
does not behave the same as C99's cabs*().
</p>
<p><b>Proposed resolution:</b></p>
<p>
This depends on the intention behind the introduction of fabs().
</p>
<p>
If the intention was to provide a /complex/ valued function that
calculates the magnitude of its argument, this should be
explicitly specified. In TR1, the categorization under "C
compatibility" is definitely wrong, since C99 does not provide
such a complex valued function.
</p>
<p>
Also, it remains questionable if such a complex valued function
is really needed, since complex&lt;T&gt; supports construction and
assignment from real valued arguments. There is no difference
in observable behaviour between
</p>
<blockquote><pre> complex&lt;double&gt; x, y;
y = fabs(x);
complex&lt;double&gt; z(fabs(x));
</pre></blockquote>
<p>
and
</p>
<blockquote><pre> complex&lt;double&gt; x, y;
y = abs(x);
complex&lt;double&gt; z(abs(x));
</pre></blockquote>
<p>
If on the other hand the intention was to provide the intended
functionality of C99, fabs() should be either declared deprecated
or (for C++0X) removed from the standard, since the functionality
is already provided by the corresponding overloads of abs().
</p>
<hr>
<a name="596"><h3>596.&nbsp;27.8.1.3 Table 112 omits "a+" and "a+b" modes</h3></a><p><b>Section:</b>&nbsp;27.8.1.3 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-iostreams.html#lib.filebuf.members"> [lib.filebuf.members]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Thomas Plum&nbsp; <b>Date:</b>&nbsp;26 Sep 2006</p>
<p>
In testing 27.8.1.3, Table 112 (in the latest N2009 draft), we invoke
</p>
<blockquote><pre> ostr.open("somename", ios_base::out | ios_base::in | ios_base::app)
</pre></blockquote>
<p>
and we expect the open to fail, because out|in|app is not listed in
Table 92, and just before the table we see very specific words:
</p>
<blockquote>
If mode is not some combination of flags shown in the table
then the open fails.
</blockquote>
<p>
But the corresponding table in the C standard, 7.19.5.3, provides two
modes "a+" and "a+b", to which the C++ modes out|in|app and
out|in|app|binary would presumably apply.
</p>
<p><b>Proposed resolution:</b></p>
<p>
We would like to argue that the intent of Table 112 was to match the
semantics of 7.19.5.3 and that the omission of "a+" and "a+b" was
unintentional. (Otherwise there would be valid and useful behaviors
available in C file I/O which are unavailable using C++, for no
valid functional reason.)
</p>
<p>
We further request that the missing modes be explicitly restored to
the WP, for inclusion in C++0x.
</p>
<hr>
<a name="597"><h3>597.&nbsp;Decimal: The notion of 'promotion' cannot be emulated by user-defined types.</h3></a><p><b>Section:</b>&nbsp;<font color="red">Decimal 3.2</font>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Daveed Vandevoorde&nbsp; <b>Date:</b>&nbsp;5 April 2006</p>
<p>
In a private email, Daveed writes:
</p>
<blockquote>
<p>
I am not familiar with the C TR, but my guess is that the
class type approach still won't match a built-in type
approach because the notion of "promotion" cannot be
emulated by user-defined types.
</p>
<p>
Here is an example:
</p>
</blockquote>
<pre>
struct S {
S(_Decimal32 const&amp;); // Converting constructor
};
void f(S);
void f(_Decimal64);
void g(_Decimal32 d) {
f(d);
}
</pre>
<blockquote>
<p>
If _Decimal32 is a built-in type, the call f(d) will likely
resolve to f(_Decimal64) because that requires only a
promotion, whereas f(S) requires a user-defined conversion.
</p>
<p>
If _Decimal32 is a class type, I think the call f(d) will be
ambiguous because both the conversion to _Decimal64 and the
conversion to S will be user-defined conversions with neither
better than the other.
</p>
</blockquote>
<p>
Robert comments:
</p>
<p>In general, a library of arithmetic types cannot exactly emulate the
behavior of the intrinsic numeric types. There are several ways to tell
whether an implementation of the decimal types uses compiler
intrinisics or a library. For example:
</p>
<pre> _Decimal32 d1;
d1.operator+=(5); // If d1 is a builtin type, this won't compile.
</pre>
<p>
In preparing the decimal TR, we have three options:
</p>
<ol>
<li>require that the decimal types be class types</li>
<li>require that the decimal types be builtin types, like float and double</li>
<li>specify a library of class types, but allow enough implementor
latitude that a conforming implementation could instead provide builtin
types</li>
</ol>
<p>
We decided as a group to pursue option #3, but that approach implies
that implementations may not agree on the semantics of certain use
cases (first example, above), or on whether certain other cases are
well-formed (second example). Another potentially important problem is
that, under the present definition of POD, the decimal classes are not
POD types, but builtins will be.
</p>
<p>Note that neither example above implies any problems with respect to
C-to-C++ compatibility, since neither example can be expressed in C.
</p>
<p><b>Proposed resolution:</b></p>
<hr>
<a name="598"><h3>598.&nbsp;Decimal: Conversion to integral should truncate, not round.</h3></a><p><b>Section:</b>&nbsp;<font color="red">Decimal 3.2</font>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Daniel Krugler&nbsp; <b>Date:</b>&nbsp;28 May 2006</p>
<p>
In a private email, Daniel writes:
</p>
<blockquote>
<p>
I would like to
ask, what where the reason for the decision to
define the semantics of the integral conversion of the decimal types, namely
</p>
<pre>"operator long long() const;
Returns: Returns the result of the
conversion of *this to the type long long, as if
performed by the expression llrounddXX(*this)."
</pre>
<p>
where XX stands for either 32, 64, or 128,
corresponding to the proper decimal type. The
exact meaning of llrounddXX is not given in that
paper, so I compared it to the corresponding
definition given in C99, 2nd edition (ISO 9899), which says in 7.12.9.7 p. 2:
</p>
<p>
"The lround and llround functions round their
argument to the nearest integer value,
rounding halfway cases away from zero, regardless
of the current rounding direction. [..]"
</p>
<p>
Now considering the fact that integral conversion
of the usual floating-point types ("4.9
Floating-integral conversions") has truncation
semantic I wonder why this conversion behaviour
has not been transferred for the decimal types.
</p>
</blockquote>
<p>
Robert comments:
</p>
<p>
Also, there is a further error in the <b>Returns:</b> clause for converting <code>decimal::decimal128</code> to <code>long long</code>. It currently calls <code>llroundd64</code>, not <code>llroundd128</code>.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change the <b>Returns:</b> clause in 3.2.2.4 to:
</p>
<blockquote>
<b>Returns:</b> Returns the result of the conversion of <code>*this</code> to the type <code>long long</code>, as if performed by the expression <code>llroundd32(*this)</code> <ins>while the decimal rounding direction mode [3.5.2] <code>FE_DEC_TOWARD_ZERO</code> is in effect</ins>.
</blockquote>
<p>
Change the <b>Returns:</b> clause in 3.2.3.4 to:
</p>
<blockquote>
<b>Returns:</b> Returns the result of the conversion of <code>*this</code> to the type <code>long long</code>, as if performed by the expression <code>llroundd64(*this)</code> <ins>while the decimal rounding direction mode [3.5.2] <code>FE_DEC_TOWARD_ZERO</code> is in effect</ins>.
</blockquote>
<p>
Change the <b>Returns:</b> clause in 3.2.4.4 to:
</p>
<blockquote>
<b>Returns:</b> Returns the result of the conversion of <code>*this</code> to the type <code>long long</code>, as if performed by the expression <del><code>llroundd64(*this)</code></del> <ins><code>llroundd128(*this)</code> while the decimal rounding direction mode [3.5.2] <code>FE_DEC_TOWARD_ZERO</code> is in effect</ins>.
</blockquote>
<hr>
<a name="599"><h3>599.&nbsp;Decimal: Say "octets" instead of "bytes."</h3></a><p><b>Section:</b>&nbsp;<font color="red">Decimal 3.1</font>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Daniel Krugler&nbsp; <b>Date:</b>&nbsp;28 May 2006</p>
<p>
Daniel writes in a private email:
</p>
<blockquote>
<p>
- 3.1 'Decimal type encodings' says in its note:
</p>
<p>
"this implies that
sizeof(std::decimal::decimal32) == 4,
sizeof(std::decimal::decimal64) == 8, and
sizeof(std::decimal::decimal128) == 16."
</p><p>
</p>
This is a wrong assertion, because the definition
of 'byte' in 1.7 'The C+ + memory model' of ISO
14882 (2nd edition) does not specify that a byte
must be necessarily 8 bits large, which would be
necessary to compare with the specified bit sizes
of the types decimal32, decimal64, and decimal128.
<p></p>
</blockquote>
<p><b>Proposed resolution:</b></p>
<p>
Change 3.1 as follows:
</p>
<blockquote>
<p>
The three decimal encoding formats defined in IEEE-754R correspond to the three decimal floating types as follows:
</p>
<ul>
<li>
decimal32 is a <em>decimal32</em> number, which is encoded in four consecutive <del>bytes</del> <ins>octets</ins> (32 bits)
</li>
<li>
decimal64 is a <em>decimal64</em> number, which is encoded in eight consecutive <del>bytes</del> <ins>octets</ins> (64 bits)
</li>
<li>
decimal128 is a <em>decimal128</em> number, which is encoded in 16 consecutive <del>bytes</del> <ins>octets</ins> (128 bits)
</li>
</ul>
<p>
<del>[<i>Note:</i> this implies that <code>sizeof(std::decimal::decimal32) == 4</code>, <code>sizeof(std::decimal::decimal64) == 8</code>, and <code>sizeof(std::decimal::decimal128) == 16</code>. <i>--end note</i>]</del>
</p>
</blockquote>
<hr>
<a name="600"><h3>600.&nbsp;Decimal: Wrong parameters for wcstod* functions</h3></a><p><b>Section:</b>&nbsp;<font color="red">Decimal 3.9</font>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Daniel Krugler&nbsp; <b>Date:</b>&nbsp;28 May 2006</p>
<p>
Daniel writes:
</p>
<blockquote>
- 3.9.1 'Additions to &lt;cwchar&gt;' provides wrong
signatures to the wcstod32, wcstod64, and
wcstod128 functions ([the parameters have type pointer-to-] char instead of wchar_t).
</blockquote>
<p><b>Proposed resolution:</b></p>
<p>
Change "3.9.1 Additions to <code>&lt;cwchar&gt;</code> synopsis" to:
</p>
<pre> namespace std {
namespace decimal {
// 3.9.2 wcstod functions:
decimal32 wcstod32 (const <del>char</del> <ins>wchar_t</ins> * nptr, <del>char</del> <ins>wchar_t</ins> ** endptr);
decimal64 wcstod64 (const <del>char</del> <ins>wchar_t</ins> * nptr, <del>char</del> <ins>wchar_t</ins> ** endptr);
decimal128 wcstod128 (const <del>char</del> <ins>wchar_t</ins> * nptr, <del>char</del> <ins>wchar_t</ins> ** endptr);
}
}
</pre>
<hr>
<a name="601"><h3>601.&nbsp;Decimal: numeric_limits typos</h3></a><p><b>Section:</b>&nbsp;<font color="red">Decimal 3.3</font>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Daniel Krugler&nbsp; <b>Date:</b>&nbsp;28 May 2006</p>
<p>
Daniel writes in a private email:
</p>
<blockquote>
<p>
- 3.3 'Additions to header &lt;limits&gt;' contains two
errors in the specialisation of numeric_limits&lt;decimal::decimal128&gt;:
</p>
<ol>
<li>The static member max() returns DEC128_MIN, this should be DEC128_MAX.</li>
<li>The static member digits is assigned to 384,
this should be 34 (Probably mixed up with the
max. exponent for decimal::decimal64).</li>
</ol>
</blockquote>
<p><b>Proposed resolution:</b></p>
<p>
In "3.3 Additions to header <code>&lt;limits&gt;</code>" change numeric_limits&lt;decimal::decimal128&gt; as follows:
</p>
<pre> template&lt;&gt; class numeric_limits&lt;decimal::decimal128&gt; {
public:
static const bool is_specialized = true;
static decimal::decimal128 min() throw() { return DEC128_MIN; }
static decimal::decimal128 max() throw() { return <del>DEC128_MIN;</del> <ins>DEC128_MAX;</ins> }
static const int digits = <del>384</del> <ins>34</ins>;
/* ... */
</pre>
<hr>
<a name="602"><h3>602.&nbsp;Decimal: "generic floating type" not defined.</h3></a><p><b>Section:</b>&nbsp;<font color="red">Decimal 3</font>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Daniel Krugler&nbsp; <b>Date:</b>&nbsp;28 May 2006</p>
<p>
The document uses the term "generic floating types," but defines it nowhere.
</p>
<p><b>Proposed resolution:</b></p>
<p>
Change the first paragraph of "3 Decimal floating-point types" as follows:
</p>
<blockquote>
This Technical Report introduces three decimal floating-point types, named
decimal32, decimal64, and decimal128. The set of values of type decimal32 is a
subset of the set of values of type decimal64; the set of values of the type
decimal64 is a subset of the set of values of the type decimal128. Support for
decimal128 is optional. <ins>These types supplement the Standard C++ types
<code>float</code>, <code>double</code>, and <code>long double</code>, which are
collectively described as the <i>basic floating types</i></ins>.
</blockquote>
<hr>
<a name="603"><h3>603.&nbsp;Decimal: Trivially simplifying decimal classes.</h3></a><p><b>Section:</b>&nbsp;<font color="red">Decimal 3</font>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;28 May 2006</p>
<p>In c++std-lib-17198, Martin writes:</p>
<blockquote>
Each of the three classes proposed in the paper (decimal32, decimal64,
and decimal128) explicitly declares and specifies the semantics of its
copy constructor, copy assignment operator, and destructor. Since the
semantics of all three functions are identical to the trivial versions
implicitly generated by the compiler in the absence of any declarations
it is safe to drop them from the spec. This change would make the
proposed classes consistent with other similar classes already in the
standard (e.g., std::complex).
</blockquote>
<p><b>Proposed resolution:</b></p>
<p>
Change "3.2.2 Class <code>decimal32</code>" as follows:
</p>
<pre> namespace std {
namespace decimal {
class decimal32 {
public:
// 3.2.2.1 construct/copy/destroy:
decimal32();
<del>decimal32(const decimal32 &amp; d32);</del>
<del>decimal32 &amp; operator=(const decimal32 &amp; d32);</del>
<del>~decimal32();</del>
/* ... */
</pre>
<p>
Change "3.2.2.1 construct/copy/destroy" as follows:
</p>
<pre> decimal32();
Effects: Constructs an object of type decimal32 with the value 0;
<del>decimal32(const decimal32 &amp; d32);</del>
<del>decimal32 &amp; operator=(const decimal32 &amp; d32);</del>
<del>Effects: Copies an object of type decimal32.</del>
<del>~decimal32();</del>
<del>Effects: Destroys an object of type decimal32.</del>
</pre>
<p>
Change "3.2.3 Class <code>decimal64</code>" as follows:
</p>
<pre> namespace std {
namespace decimal {
class decimal64 {
public:
// 3.2.3.1 construct/copy/destroy:
decimal64();
<del>decimal64(const decimal64 &amp; d64);</del>
<del>decimal64 &amp; operator=(const decimal64 &amp; d64);</del>
<del>~decimal64();</del>
/* ... */
</pre>
<p>
Change "3.2.3.1 construct/copy/destroy" as follows:
</p>
<pre> decimal64();
Effects: Constructs an object of type decimal64 with the value 0;
<del>decimal64(const decimal64 &amp; d64);</del>
<del>decimal64 &amp; operator=(const decimal64 &amp; d64);</del>
<del>Effects: Copies an object of type decimal64.</del>
<del>~decimal64();</del>
<del>Effects: Destroys an object of type decimal64.</del>
</pre>
<p>
Change "3.2.4 Class <code>decimal128</code>" as follows:
</p>
<pre> namespace std {
namespace decimal {
class decimal128 {
public:
// 3.2.4.1 construct/copy/destroy:
decimal128();
<del>decimal128(const decimal128 &amp; d128);</del>
<del>decimal128 &amp; operator=(const decimal128 &amp; d128);</del>
<del>~decimal128();</del>
/* ... */
</pre>
<p>
Change "3.2.4.1 construct/copy/destroy" as follows:
</p>
<pre> decimal128();
Effects: Constructs an object of type decimal128 with the value 0;
<del>decimal128(const decimal128 &amp; d128);</del>
<del>decimal128 &amp; operator=(const decimal128 &amp; d128);</del>
<del>Effects: Copies an object of type decimal128.</del>
<del>~decimal128();</del>
<del>Effects: Destroys an object of type decimal128.</del>
</pre>
<hr>
<a name="604"><h3>604.&nbsp;Decimal: Storing a reference to a facet unsafe.</h3></a><p><b>Section:</b>&nbsp;<font color="red">Decimal 3</font>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Review">Review</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;28 May 2006</p>
<p>
In c++std-lib-17197, Martin writes:
</p>
<blockquote>
The extended_num_get and extended_num_put facets are designed
to store a reference to a num_get or num_put facet which the
extended facets delegate the parsing and formatting of types
other than decimal. One form of the extended facet's ctor (the
default ctor and the size_t overload) obtains the reference
from the global C++ locale while the other form takes this
reference as an argument.
</blockquote>
<blockquote>
The problem with storing a reference to a facet in another
object (as opposed to storing the locale object in which the
facet is installed) is that doing so bypasses the reference
counting mechanism designed to prevent a facet that is still
being referenced (i.e., one that is still installed in some
locale) from being destroyed when another locale that contains
it is destroyed. Separating a facet reference from the locale
it comes from van make it cumbersome (and in some cases might
even make it impossible) for programs to prevent invalidating
the reference. (The danger of this design is highlighted in
the paper.)
</blockquote>
<blockquote>
This problem could be easily avoided by having the extended
facets store a copy of the locale from which they would extract
the base facet either at construction time or when needed. To
make it possible, the forms of ctors of the extended facets that
take a reference to the base facet would need to be changed to
take a locale argument instead.
</blockquote>
<p><b>Proposed resolution:</b></p>
<p>
1. Change the <code>extended_num_get</code> synopsis in 3.10.2 as follows:
</p>
<pre> extended_num_get(const <del>std::num_get&lt;charT, InputIterator&gt;</del> <ins>std::locale</ins> &amp; <i>b</i>, size_t <i>refs</i> = 0);
/* ... */
<del>// <i>const std::num_get&lt;charT, InputIterator&gt; &amp; <b>base</b></i>; <i><b>exposition only</b></i></del>
<ins>// <i>std::locale <b>baseloc</b></i>; <i><b>exposition only</b></i></ins>
</pre>
<p>
2. Change the description of the above constructor in 3.10.2.1:
</p>
<pre> extended_num_get(const <del>std::num_get&lt;charT, InputIterator&gt;</del> <ins>std::locale</ins> &amp; <i>b</i>, size_t <i>refs</i> = 0);
</pre>
<blockquote>
<p>
<b>Effects:</b> Constructs an <code>extended_num_get</code> facet as if by:
</p>
<pre> extended_num_get(const <del>std::num_get&lt;charT, InputIterator&gt;</del> <ins>std::locale</ins> &amp; <i>b</i>, size_t <i>refs</i> = 0)
: facet(<i>refs</i>), <i>base<ins>loc</ins></i>(<i>b</i>)
{ /* ... */ }
</pre>
<p>
<del><b>Notes:</b> Care must be taken by the implementation to ensure that the lifetime of the facet referenced by <i>base</i> exceeds that of the resulting <code>extended_num_get</code> facet.</del>
</p>
</blockquote>
<p>
3. Change the <b>Returns:</b> clause for <code>do_get(iter_type, iter_type, ios_base &amp;, ios_base::iostate &amp;, bool &amp;) const</code>, <i>et al</i> to
</p>
<blockquote>
<b>Returns:</b> <code><del><i>base</i></del> <ins>std::use_facet&lt;std::num_get&lt;charT, InputIterator&gt; &gt;(<i>baseloc</i>)</ins>.get(<i>in</i>, <i>end</i>, <i>str</i>, <i>err</i>, <i>val</i>)</code>.
</blockquote>
<p>
4. Change the <code>extended_num_put</code> synopsis in 3.10.3 as follows:
</p>
<pre> extended_num_put(const <del>std::num_put&lt;charT, OutputIterator&gt;</del> <ins>std::locale</ins> &amp; <i>b</i>, size_t <i>refs</i> = 0);
/* ... */
<del>// <i>const std::num_put&lt;charT, OutputIterator&gt; &amp; <b>base</b></i>; <i><b>exposition only</b></i></del>
<ins>// <i>std::locale <b>baseloc</b></i>; <i><b>exposition only</b></i></ins>
</pre>
<p>
5. Change the description of the above constructor in 3.10.3.1:
</p>
<pre> extended_num_put(const <del>std::num_put&lt;charT, OutputIterator&gt;</del> <ins>std::locale</ins> &amp; <i>b</i>, size_t <i>refs</i> = 0);
</pre>
<blockquote>
<p>
<b>Effects:</b> Constructs an <code>extended_num_put</code> facet as if by:
</p>
<pre> extended_num_put(const <del>std::num_put&lt;charT, OutputIterator&gt;</del> <ins>std::locale</ins> &amp; <i>b</i>, size_t <i>refs</i> = 0)
: facet(<i>refs</i>), <i>base<ins>loc</ins></i>(<i>b</i>)
{ /* ... */ }
</pre>
<p>
<del><b>Notes:</b> Care must be taken by the implementation to ensure that the lifetime of the facet referenced by <i>base</i> exceeds that of the resulting <code>extended_num_put</code> facet.</del>
</p>
</blockquote>
<p>
6. Change the <b>Returns:</b> clause for <code>do_put(iter_type, ios_base &amp;, char_type, bool &amp;) const</code>, <i>et al</i> to
</p>
<blockquote>
<b>Returns:</b> <code><del><i>base</i></del> <ins>std::use_facet&lt;std::num_put&lt;charT, OutputIterator&gt; &gt;(<i>baseloc</i>)</ins>.put(<i>s</i>, <i>f</i>, <i>fill</i>, <i>val</i>)</code>.
</blockquote>
<p><i>[
Redmond: We would prefer to rename "extended" to "decimal".
]</i></p>
<hr>
<a name="605"><h3>605.&nbsp;Decimal: &lt;decfloat.h&gt; doesn't live here anymore.</h3></a><p><b>Section:</b>&nbsp;<font color="red">Decimal 3.4</font>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Ready">Ready</a>&nbsp; <b>Submitter:</b>&nbsp;Robert Klarer&nbsp; <b>Date:</b>&nbsp;17 October 2006</p>
<p>In Berlin, WG14 decided to drop the &lt;decfloat.h&gt; header. The
contents of that header have been moved into &lt;float.h&gt;. For the
sake of C compatibility, we should make corresponding changes.
</p>
<p><b>Proposed resolution:</b></p>
<p>
1. Change the heading of subclause 3.4, "Headers <code>&lt;cdecfloat&gt;</code> and <code>&lt;decfloat.h&gt;</code>" to "Additions to headers <code>&lt;cfloat&gt;</code> and <code>&lt;float.h&gt;</code>."
</p>
<p>
2. Change the text of subclause 3.4 as follows:
</p>
<blockquote>
<p>
<del>The standard C++ headers <code>&lt;cfloat&gt;</code> and <code>&lt;float.h&gt;</code> define characteristics of the floating-point types <code>float</code>, <code>double</code>, and <code>long double</code>. Their contents remain unchanged by this Technical Report.</del>
</p>
<p>
<del>Headers <code>&lt;cdecfloat&gt;</code> and <code>&lt;decfloat.h&gt;</code> define characteristics of the decimal floating-point types <code>decimal32</code>, <code>decimal64</code>, and <code>decimal128</code>. As well, <code>&lt;decfloat.h&gt;</code> defines the convenience typedefs <code>_Decimal32</code>, <code>_Decimal64</code>, and <code>_Decimal128</code>, for compatibilty with the C programming language.</del>
</p>
<p>
<ins>The header <code>&lt;cfloat&gt;</code> is described in [tr.c99.cfloat]. The header <code>&lt;float.h&gt;</code>
is described in [tr.c99.floath]. These headers are extended by this
Technical Report to define characteristics of the decimal
floating-point types <code>decimal32</code>, <code>decimal64</code>, and <code>decimal128</code>. As well, <code>&lt;float.h&gt;</code> is extended to define the convenience typedefs <code>_Decimal32</code>, <code>_Decimal64</code>, and <code>_Decimal128</code> for compatibility with the C programming language.</ins>
</p>
</blockquote>
<p>
3. Change the heading of subclause 3.4.1, "Header <code>&lt;cdecfloat&gt;</code> synopsis" to "Additions to header <code>&lt;cfloat&gt;</code> synopsis."
</p>
<p>
4. Change the heading of subclause 3.4.2, "Header <code>&lt;decfloat.h&gt;</code> synopsis" to "Additions to header <code>&lt;float.h&gt;</code> synopsis."
</p>
<p>
5. Change the contents of 3.4.2 as follows:
</p>
<pre> <del>#include &lt;cdecfloat&gt;</del>
// <i>C-compatibility convenience typedefs:</i>
typedef std::decimal::decimal32 _Decimal32;
typedef std::decimal::decimal64 _Decimal64;
typedef std::decimal::decimal128 _Decimal128;
</pre>
<hr>
<a name="606"><h3>606.&nbsp;Decimal: allow narrowing conversions</h3></a><p><b>Section:</b>&nbsp;<font color="red">Decimal 3.2</font>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#Open">Open</a>&nbsp; <b>Submitter:</b>&nbsp;Martin Sebor&nbsp; <b>Date:</b>&nbsp;15 June 2006</p>
<p>
In c++std-lib-17205, Martin writes:
</p>
<blockquote>
...was it a deliberate design choice to make narrowing assignments
ill-formed while permitting narrowing compound assignments? For
instance:
</blockquote>
<pre> decimal32 d32;
decimal64 d64;
d32 = 64; // error
d32 += 64; // okay
</pre>
<p>
In c++std-lib-17229, Robert responds:
</p>
<blockquote>It is a vestige of an old idea that I forgot to remove from
the paper. Narrowing assignments should be permitted. The bug is that
the converting constructors that cause narrowing should not be
explicit. Thanks for pointing this out.
</blockquote>
<p><b>Proposed resolution:</b></p>
<p>
1. In "3.2.2 Class <code>decimal32</code>" synopsis, remove the <code>explicit</code> specifier from the narrowing conversions:
</p>
<pre> // <i>3.2.2.2 conversion from floating-point type:</i>
<del>explicit</del> decimal32(decimal64 <i>d64</i>);
<del>explicit</del> decimal32(decimal128 <i>d128</i>);
</pre>
<p>
2. Do the same thing in "3.2.2.2. Conversion from floating-point type."
</p>
<p>
3. In "3.2.3 Class <code>decimal64</code>" synopsis, remove the <code>explicit</code> specifier from the narrowing conversion:
</p>
<pre> // <i>3.2.3.2 conversion from floating-point type:</i>
<del>explicit</del> decimal64(decimal128 <i>d128</i>);
</pre>
<p>
4. Do the same thing in "3.2.3.2. Conversion from floating-point type."
</p>
<p><i>[
Redmond: We prefer explicit conversions for narrowing and implicit for widening.
]</i></p>
<hr>
<a name="607"><h3>607.&nbsp;Concern about short seed vectors</h3></a><p><b>Section:</b>&nbsp;26.4.7.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.rand.dist.iunif"> [lib.rand.dist.iunif]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Charles Karney&nbsp; <b>Date:</b>&nbsp;26 Oct 2006</p>
<p>
Short seed vectors of 32-bit quantities all result in different states. However
this is not true of seed vectors of 16-bit (or smaller) quantities. For example
these two seeds
</p>
<blockquote><pre>unsigned short seed = {1, 2, 3};
unsigned short seed = {1, 2, 3, 0};
</pre></blockquote>
<p>
both pack to
</p>
<blockquote><pre>unsigned seed = {0x20001, 0x3};
</pre></blockquote>
<p>
yielding the same state.
</p>
<p><b>Proposed resolution:</b></p>
<p>
In 26.4.7.1[rand.util.seedseq]/8a, replace
</p>
<blockquote>
<p>
Set <tt>begin[0]</tt> to <tt>5489 + <del>s</del><ins>N</ins></tt>.
</p>
<p>
where <tt>N</tt> is the bit length of the sequence used to construct the
seed_seq in 26.4.7.1/6 [rand.util.seedseq]. (This quantity is called <tt>n</tt>
in 26.4.7.1/6 [rand.util.seedseq], but <tt>n</tt> has a different meaning in
26.4.7.1/8 [rand.util.seedseq]. We have <tt>32^(s-1) &lt; N &lt;= 32^s</tt>.) Now
</p>
<blockquote><pre>unsigned short seed = {1, 2, 3, 0};
unsigned seed = {0x20001, 0x3};
</pre></blockquote>
<p>
are equivalent (<tt>N = 64</tt>), but
</p>
<blockquote><pre>unsigned short seed = {1, 2, 3};
</pre></blockquote>
<p>
gives a distinct state (<tt>N = 48</tt>).
</p>
</blockquote>
<hr>
<a name="608"><h3>608.&nbsp;Unclear seed_seq construction details</h3></a><p><b>Section:</b>&nbsp;26.4.7.1 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.rand.dist.iunif"> [lib.rand.dist.iunif]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Charles Karney&nbsp; <b>Date:</b>&nbsp;26 Oct 2006</p>
<p>
In 26.4.7.1 [rand.util.seedseq] /6, the order of packing the inputs into b and the
treatment of signed quantities is unclear. Better to spell it out.
</p>
<p><b>Proposed resolution:</b></p>
<blockquote><pre>b = sum( unsigned(begin[i]) 2^(w i), 0 &lt;= i &lt; end-begin )
</pre></blockquote>
<p>
where <tt>w</tt> is the bit-width of the InputIterator.
</p>
<hr>
<a name="609"><h3>609.&nbsp;missing static const</h3></a><p><b>Section:</b>&nbsp;26.4.4.2 <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lib-numerics.html#lib.rand.eng.mers"> [lib.rand.eng.mers]</a>&nbsp; <b>Status:</b>&nbsp;<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#New">New</a>&nbsp; <b>Submitter:</b>&nbsp;Walter E. Brown&nbsp; <b>Date:</b>&nbsp;2 Nov 2006</p>
<p>
In preparing N2111, an error on my part resulted in the omission of the
following line from the template synopsis in the cited section:
</p>
<blockquote><pre>static const size_t word_size = w;
</pre></blockquote>
<p>
(This same constant is found, for example, in 26.4.3.3 [rand.eng.sub].)
</p>
<p><b>Proposed resolution:</b></p>
<p>
Add the above declaration as the first line after the comment in [rand.adapt.ibits] p4:
</p>
<blockquote><pre>// engine characteristics
<ins>static const size_t word_size = w;</ins>
</pre></blockquote>
<p>
and accept my apologies for the oversight.
</p>
<p>----- End of document -----</p>
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