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<title>Issue 354: Associative container lower/upper bound requirements</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="354"><a href="lwg-defects.html#354">354</a>. Associative container lower/upper bound requirements</h3>
<p><b>Section:</b> 23.2.7 <a href="https://wg21.link/associative.reqmts">[associative.reqmts]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Hans Aberg <b>Opened:</b> 2001-12-17 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#associative.reqmts">active issues</a> in [associative.reqmts].</p>
<p><b>View all other</b> <a href="lwg-index.html#associative.reqmts">issues</a> in [associative.reqmts].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Discussions in the thread "Associative container lower/upper bound
requirements" on comp.std.c++ suggests that there is a defect in the
C++ standard, Table 69 of section 23.1.2, "Associative containers",
[lib.associative.reqmts].  It currently says:</p>

<blockquote>
<p>
a.find(k): returns an iterator pointing to an element with the key equivalent to
k, or a.end() if such an element is not found.
</p>

<p>
a.lower_bound(k): returns an iterator pointing to the first element with
key not less than k.
</p>

<p>
a.upper_bound(k): returns an iterator pointing to the first element with
key greater than k.
</p>
</blockquote>

<p>
We have "or a.end() if such an element is not found" for
<code>find</code>, but not for <code>upper_bound</code> or
<code>lower_bound</code>.  As the text stands, one would be forced to
insert a new element into the container and return an iterator to that
in case the sought iterator does not exist, which does not seem to be
the intention (and not possible with the "const" versions).
</p>


<p id="res-354"><b>Proposed resolution:</b></p>

<p>Change Table 69 of section 23.2.7 <a href="https://wg21.link/associative.reqmts">[associative.reqmts]</a> indicated entries
to:</p>

<blockquote>
<p>
a.lower_bound(k): returns an iterator pointing to the first element with
key not less than k, or a.end() if such an element is not found.
</p>

<p>
a.upper_bound(k): returns an iterator pointing to the first element with
key greater than k, or a.end() if such an element is not found.
</p>
</blockquote>

<p><i>[Cura&ccedil;ao: LWG reviewed PR.]</i></p>








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