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<title>Issue 2341: Inconsistency between basic_ostream::seekp(pos) and basic_ostream::seekp(off, dir)</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#C++14">C++14</a> status.</em></p>
<h3 id="2341"><a href="lwg-defects.html#2341">2341</a>. Inconsistency between <code>basic_ostream::seekp(pos)</code> and <code>basic_ostream::seekp(off, dir)</code></h3>
<p><b>Section:</b> 31.7.6.2.5 <a href="https://wg21.link/ostream.seeks">[ostream.seeks]</a> <b>Status:</b> <a href="lwg-active.html#C++14">C++14</a>
 <b>Submitter:</b> Marshall Clow  <b>Opened:</b> 2013-10-21 <b>Last modified:</b> 2017-07-05</p>
<p><b>Priority: </b>0
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++14">C++14</a> status.</p>
<p><b>Discussion:</b></p>
<p>
In 31.7.6.2.5 <a href="https://wg21.link/ostream.seeks">[ostream.seeks]</a>, we have:
</p>
<blockquote><pre>
basic_ostream&lt;charT,traits&gt;&amp; seekp(pos_type pos);
</pre><blockquote>
<p>
-3- <i>Effects:</i> If <code>fail() != true</code>, executes <code>rdbuf()-&gt;pubseekpos(pos, ios_base::out)</code>. In case of failure, 
the function calls <code>setstate(failbit)</code> (which may throw <code>ios_base::failure</code>).
<p/>
-4- <i>Returns:</i> <code>*this</code>.
</p>
</blockquote></blockquote>
<blockquote><pre>
basic_ostream&lt;charT,traits&gt;&amp; seekp(off_type off, ios_base::seekdir dir);
</pre><blockquote>
<p>
-5- <i>Effects:</i> If <code>fail() != true</code>, executes <code>rdbuf()-&gt;pubseekoff(off, dir, ios_base::out)</code>.
<p/>
-6- <i>Returns:</i> <code>*this</code>.
</p>
</blockquote></blockquote>
<p>
The first call is required to set the <code>failbit</code> on failure, but the second is not
<p/>
So (given two ostreams, <code>os1</code> and <code>os2</code>) the following code (confusingly) works:
</p>
<blockquote><pre>
os1.seekp(-1);
assert(os1.fail());

os2.seekp(-1, std::ios_base::beg);
assert(os2.good());
</pre></blockquote>
<p>
Note that the description of <code>basic_istream&lt;charT,traits&gt;&amp; seekg(off_type off, ios_base::seekdir dir)</code> in 
31.7.5.4 <a href="https://wg21.link/istream.unformatted">[istream.unformatted]</a> p43 <em>does</em> require setting <code>failbit</code>.
</p>

<p><i>[Issaquah 2014-02-11: Move to Immediate]</i></p>




<p id="res-2341"><b>Proposed resolution:</b></p>
<p>This wording is relative to N3797.</p>

<ol>
<li><p>Modify 31.7.6.2.5 <a href="https://wg21.link/ostream.seeks">[ostream.seeks]</a>p5 as indicated:</p>

<blockquote><pre>
basic_ostream&lt;charT,traits&gt;&amp; seekp(off_type off, ios_base::seekdir dir);
</pre><blockquote>
<p>
-5- <i>Effects:</i> If <code>fail() != true</code>, executes <code>rdbuf()-&gt;pubseekoff(off, dir, ios_base::out)</code>.
<ins>In case of failure, the function calls <code>setstate(failbit)</code> (which may throw <code>ios_base::failure</code>).</ins>
<p/>
-6- <i>Returns:</i> <code>*this</code>.
</p>
</blockquote></blockquote>
</li>

</ol>





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