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<title>Issue 435: bug in DR 25</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#CD1">CD1</a> status.</em></p>
<h3 id="435"><a href="lwg-defects.html#435">435</a>. bug in DR 25</h3>
<p><b>Section:</b> 27.4.4.4 <a href="https://wg21.link/string.io">[string.io]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2003-10-15 <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#string.io">issues</a> in [string.io].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>

<p>
It has been pointed out that the proposed resolution in DR <a href="lwg-defects.html#25" title="String operator&lt;&lt; uses width() value wrong (Status: TC1)">25</a><sup><a href="https://cplusplus.github.io/LWG/issue25" title="Latest snapshot">(i)</a></sup> may not be
quite up to snuff: <br/>
http://gcc.gnu.org/ml/libstdc++/2003-09/msg00147.html
</p>

<p>
It looks like Petur is right. The complete corrected text is copied below.
I think we may have have been confused by the reference to 22.2.2.2.2 and
the subsequent description of `n' which actually talks about the second
argument to sputn(), not about the number of fill characters to pad with.
</p>

<p>
So the question is: was the original text correct? If the intent was to
follow classic iostreams then it most likely wasn't, since setting width()
to less than the length of the string doesn't truncate it on output. This
is also the behavior of most implementations (except for SGI's standard
iostreams where the operator does truncate).
</p>



<p id="res-435"><b>Proposed resolution:</b></p>
<p>Change the text in 21.3.7.9, p4 from</p>
    <blockquote><p>
    If bool(k) is true, inserts characters as if by calling
    os.rdbuf()->sputn(str.data(), n), padding as described in stage 3
    of lib.facet.num.put.virtuals, where n is the larger of os.width()
    and str.size(); 
    </p></blockquote>
<p>to</p>
    <blockquote><p>
    If bool(k) is true, determines padding as described in
    lib.facet.num.put.virtuals, and then inserts the resulting
    sequence of characters <code>seq</code> as if by calling
    <code>os.rdbuf()->sputn(seq, n)</code>, where <code>n</code> is the larger of
    <code>os.width()</code> and <code>str.size()</code>;
     </p></blockquote>

<p><i>[Kona: it appears that neither the original wording, DR25, nor the
  proposed resolution, is quite what we want.  We want to say that
  the string will be output, padded to os.width() if necessary.  We
  don't want to duplicate the padding rules in clause 22, because
  they're complicated, but we need to be careful because they weren't
  quite written with quite this case in mind.  We need to say what
  the character sequence is, and then defer to clause 22.  Post-Kona:
  Benjamin provided wording.]</i></p>







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