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<title>Issue 614: std::string allocator requirements still inconsistent</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="614"><a href="lwg-closed.html#614">614</a>. <code>std::string</code> allocator requirements still inconsistent</h3>
<p><b>Section:</b> 27.4.3 <a href="https://wg21.link/basic.string">[basic.string]</a> <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> Bo Persson <b>Opened:</b> 2006-12-05 <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#basic.string">active issues</a> in [basic.string].</p>
<p><b>View all other</b> <a href="lwg-index.html#basic.string">issues</a> in [basic.string].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>
<p>
This is based on N2134, where 21.3.1/2 states:
"... The Allocator object used shall be a copy of the Allocator object 
passed to the basic_string object's constructor or, if the constructor does 
not take an Allocator argument, a copy of a default-constructed Allocator 
object."
</p>
<p>
Section 21.3.2/1 lists two constructors:
</p>
<blockquote><pre>
basic_string(const basic_string&lt;charT,traits,Allocator&gt;&amp; str );

basic_string(const basic_string&lt;charT,traits,Allocator&gt;&amp; str ,
             size_type pos , size_type n = npos,
             const Allocator&amp; a = Allocator());
</pre></blockquote>
<p>
and then says "In the first form, the Allocator value used is copied from 
str.get_allocator().", which isn't an option according to 21.3.1.
</p>
<p><i>[
Batavia:  We need blanket statement to the effect of:
]</i></p>


<ol>
<li>If an allocator is passed in, use it, or,</li>
<li>If a string is passed in, use its allocator.</li>
</ol>
<p><i>[
Review constructors and functions that return a string; make sure we follow these
rules (substr, operator+, etc.).  Howard to supply wording.
]</i></p>


<p><i>[
Bo adds:  The new container constructor which takes only a <code>size_type</code> is not
consistent with 23.2 <a href="https://wg21.link/container.requirements">[container.requirements]</a>, p9 which says in part:
]</i></p>


<blockquote><p>
All other constructors for these container types take an
<code>Allocator&amp;</code> argument (20.1.2), an allocator whose value type
is the same as the container's value type. A copy of this argument is
used for any memory allocation performed, by these constructors and by
all member functions, during the lifetime of each container object.
</p></blockquote>

<p><i>[
post Bellevue: We re-confirm that the issue is real. Pablo will provide wording.
]</i></p>


<p><i>[
2009-07 Frankfurt
]</i></p>


<blockquote><p>
Move to NAD.
</p></blockquote>



<p id="res-614"><b>Proposed resolution:</b></p>
<p>
</p>





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