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re PR libstdc++/59687 (The description of ios::noreplace is hilarious) 

PR libstdc++/59687
	* doc/xml/manual/backwards_compatibility.xml
	(backwards.third.nocreate_noreplace): Correct and expand.

From-SVN: r206525
This commit is contained in:
Jonathan Wakely 2014-01-10 14:30:27 +00:00 committed by Jonathan Wakely
parent 92bf138207
commit b1fb52ca2e
2 changed files with 21 additions and 10 deletions
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4
libstdc++-v3/ChangeLog
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@ -7,6 +7,10 @@
and update for C++11. and update for C++11.
* doc/xml/manual/ctype.xml (std.localization.facet.ctype): Likewise. * doc/xml/manual/ctype.xml (std.localization.facet.ctype): Likewise.
PR libstdc++/59687
* doc/xml/manual/backwards_compatibility.xml
(backwards.third.nocreate_noreplace): Correct and expand.
2014-01-09 Jonathan Wakely <jwakely@redhat.com> 2014-01-09 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/59738 PR libstdc++/59738

27
libstdc++-v3/doc/xml/manual/backwards_compatibility.xml
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@ -782,18 +782,25 @@ AC_DEFUN([AC_HEADER_EXT_HASH_SET], [
</title></info> </title></info>
<para> The existence of <code>ios::nocreate</code> being used for <para>Historically these flags were used with iostreams to control whether
input-streams has been confirmed, most probably because the author new files are created or not when opening a file stream, similar to the
thought it would be more correct to specify nocreate explicitly. So <code>O_CREAT</code> and <code>O_EXCL</code> flags for the
it can be left out for input-streams. <function>open(2)</function> system call. Because iostream modes correspond
to <function>fopen(3)</function> modes these flags are not supported.
For input streams a new file will not be created anyway, so
<code>ios::nocreate</code> is not needed.
For output streams, a new file will be created if it does not exist, which is
consistent with the behaviour of <function>fopen</function>.
</para> </para>
<para>For output streams, <quote>nocreate</quote> is probably the default, <para>When one of these flags is needed a possible alternative is to attempt
unless you specify <code>std::ios::trunc</code> ? To be safe, you can to open the file using <type>std::ifstream</type> first to determine whether
open the file for reading, check if it has been opened, and then the file already exists or not. This may not be reliable however, because
decide whether you want to create/replace or not. To my knowledge, whether the file exists or not could change between opening the
even older implementations support <code>app</code>, <code>ate</code> <type>std::istream</type> and re-opening with an output stream. If you need
and <code>trunc</code> (except for <code>app</code> ?). to check for existence and open a file as a single operation then you will
need to use OS-specific facilities outside the C++ standard library, such
as <function>open(2)</function>.
</para> </para>
</section> </section>