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<title>Issue 467: char_traits::lt(), compare(), and memcmp()</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="467"><a href="lwg-defects.html#467">467</a>. char_traits::lt(), compare(), and memcmp()</h3>
<p><b>Section:</b> 27.2.4.2 <a href="https://wg21.link/char.traits.specializations.char">[char.traits.specializations.char]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2004-06-28 <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#char.traits.specializations.char">issues</a> in [char.traits.specializations.char].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>

<p>
Table 37 describes the requirements on Traits::compare() in terms of
those on Traits::lt(). 21.1.3.1, p6 requires char_traits&lt;char>::lt()
to yield the same result as operator&lt;(char, char).
</p>

<p>
Most, if not all, implementations of char_traits&lt;char>::compare()
call memcmp() for efficiency. However, the C standard requires both
memcmp() and strcmp() to interpret characters under comparison as
unsigned, regardless of the signedness of char. As a result, all
these char_traits implementations fail to meet the requirement
imposed by Table 37 on compare() when char is signed.
</p>


<p>Read email thread starting with c++std-lib-13499 for more. </p>


<p id="res-467"><b>Proposed resolution:</b></p>


<p>Change 21.1.3.1, p6 from</p>
<blockquote><p>
    The two-argument members assign, eq, and lt are defined identically
    to the built-in operators =, ==, and &lt; respectively.
</p></blockquote>
<p>to</p>
<blockquote><p>
  The two-argument member assign is defined identically to
  the built-in operator =. The two
  argument members eq and lt are defined identically to
  the built-in operators == and &lt; for type unsigned char.
</p></blockquote>

<p><i>[Redmond: The LWG agreed with this general direction, but we
  also need to change <code>eq</code> to be consistent with this change.
  Post-Redmond: Martin provided wording.]</i></p>






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