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<title>Issue 69: Must elements of a vector be contiguous?</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#TC1">TC1</a> status.</em></p>
<h3 id="69"><a href="lwg-defects.html#69">69</a>. Must elements of a vector be contiguous?</h3>
<p><b>Section:</b> 23.3.13 <a href="https://wg21.link/vector">[vector]</a> <b>Status:</b> <a href="lwg-active.html#TC1">TC1</a>
 <b>Submitter:</b> Andrew Koenig <b>Opened:</b> 1998-07-29 <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#vector">issues</a> in [vector].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#TC1">TC1</a> status.</p>
<p><b>Discussion:</b></p>
<p>The issue is this: Must the elements of a vector be in contiguous memory?</p>

<p>(Please note that this is entirely separate from the question of
whether a vector iterator is required to be a pointer; the answer to
that question is clearly &quot;no,&quot; as it would rule out
debugging implementations)</p>


<p id="res-69"><b>Proposed resolution:</b></p>
<p>Add the following text to the end of 23.3.13 <a href="https://wg21.link/vector">[vector]</a>,
paragraph 1. </p>

<blockquote>
  <p>The elements of a vector are stored contiguously, meaning that if
  v is a <code>vector&lt;T, Allocator&gt;</code> where T is some type
  other than <code>bool</code>, then it obeys the identity <code>&amp;v[n]
  == &amp;v[0] + n</code> for all <code>0 &lt;= n &lt; v.size()</code>.</p>
</blockquote>


<p><b>Rationale:</b></p>
<p>The LWG feels that as a practical matter the answer is clearly
&quot;yes&quot;.  There was considerable discussion as to the best way
to express the concept of &quot;contiguous&quot;, which is not
directly defined in the standard.  Discussion included:</p>

<ul>
  <li>An operational definition similar to the above proposed resolution is 
    already used for valarray (29.6.2.4 <a href="https://wg21.link/valarray.access">[valarray.access]</a>).</li>
  <li>There is no need to explicitly consider a user-defined operator&amp; 
    because elements must be copyconstructible (23.2 <a href="https://wg21.link/container.requirements">[container.requirements]</a> para 3) 
    and copyconstructible (16.4.4.2 <a href="https://wg21.link/utility.arg.requirements">[utility.arg.requirements]</a>) specifies
    requirements for operator&amp;.</li>
  <li>There is no issue of one-past-the-end because of language rules.</li>
</ul>





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