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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.
* 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>
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>
<para> The existence of <code>ios::nocreate</code> being used for
input-streams has been confirmed, most probably because the author
thought it would be more correct to specify nocreate explicitly. So
it can be left out for input-streams.
<para>Historically these flags were used with iostreams to control whether
new files are created or not when opening a file stream, similar to the
<code>O_CREAT</code> and <code>O_EXCL</code> flags for the
<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>For output streams, <quote>nocreate</quote> is probably the default,
unless you specify <code>std::ios::trunc</code> ? To be safe, you can
open the file for reading, check if it has been opened, and then
decide whether you want to create/replace or not. To my knowledge,
even older implementations support <code>app</code>, <code>ate</code>
and <code>trunc</code> (except for <code>app</code> ?).
<para>When one of these flags is needed a possible alternative is to attempt
to open the file using <type>std::ifstream</type> first to determine whether
the file already exists or not. This may not be reliable however, because
whether the file exists or not could change between opening the
<type>std::istream</type> and re-opening with an output stream. If you need
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>
</section>