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<title>Issue 113: Missing/extra iostream sync semantics</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#NAD">NAD</a> status.</em></p>
<h3 id="113"><a href="lwg-closed.html#113">113</a>. Missing/extra iostream sync semantics</h3>
<p><b>Section:</b> 31.7.5.2 <a href="https://wg21.link/istream">[istream]</a>, 31.7.5.4 <a href="https://wg21.link/istream.unformatted">[istream.unformatted]</a> <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> Steve Clamage <b>Opened:</b> 1998-10-13 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#istream">issues</a> in [istream].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>
<p>In 27.6.1.1, class basic_istream has a member function sync, described in 27.6.1.3,
paragraph 36. </p>

<p>Following the chain of definitions, I find that the various sync functions have defined
semantics for output streams, but no semantics for input streams. On the other hand,
basic_ostream has no sync function. </p>

<p>The sync function should at minimum be added to basic_ostream, for internal
consistency. </p>

<p>A larger question is whether sync should have assigned semantics for input streams. </p>

<p>Classic iostreams said streambuf::sync flushes pending output and attempts to return
unread input characters to the source. It is a protected member function. The filebuf
version (which is public) has that behavior (it backs up the read pointer). Class
strstreambuf does not override streambuf::sync, and so sync can't be called on a
strstream. </p>

<p>If we can add corresponding semantics to the various sync functions, we should. If not,
we should remove sync from basic_istream.</p>


<p><b>Rationale:</b></p>
<p>A sync function is not needed in basic_ostream because the flush function provides the
desired functionality.</p>

<p>As for the other points, the LWG finds the standard correct as written.</p>





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