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<title>Issue 2241: &lt;cstdalign&gt; and #define of alignof</title>
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<h3 id="2241"><a href="lwg-defects.html#2241">2241</a>. <code>&lt;cstdalign&gt;</code> and <code>#define</code> of <code>alignof</code></h3>
<p><b>Section:</b> 17.14 <a href="https://wg21.link/support.runtime">[support.runtime]</a> <b>Status:</b> <a href="lwg-active.html#Resolved">Resolved</a>
 <b>Submitter:</b> Richard Smith <b>Opened:</b> 2013-02-14 <b>Last modified:</b> 2020-09-06</p>
<p><b>Priority: </b>2
</p>
<p><b>View all other</b> <a href="lwg-index.html#support.runtime">issues</a> in [support.runtime].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Resolved">Resolved</a> status.</p>
<p><b>Discussion:</b></p>
<p>
According to 17.14 <a href="https://wg21.link/support.runtime">[support.runtime]</a> p2:
</p>

<blockquote><p>
The contents of these headers are the same as the Standard C library headers [..], <code>&lt;stdalign.h&gt;</code>, [..]
</p></blockquote>

<p>
Since our base C standard is C99, which doesn't have a <code>&lt;stdalign.h&gt;</code>, the reference to a non-existing 
C header is irritating (In this context <code>&lt;stdalign.h&gt;</code> doesn't refer to the deprecated C++ header
<code>&lt;stdalign.h&gt;</code> described in  [depr.c.headers]).
<p/>
Furthermore, it would be also important that it doesn not define a macro named <code>alignof</code>, which C11 also defines 
in this header. 
<p/>
Currently we only have the following guarantee as part of 17.14 <a href="https://wg21.link/support.runtime">[support.runtime]</a> p7:
</p>

<blockquote><p>
The header <code>&lt;cstdalign&gt;</code> and the header <code>&lt;stdalign.h&gt;</code> shall not define a macro named 
<code>alignas</code>.
</p></blockquote>

<p>
It is unclear what the better strategy is: Striking the reference to <code>&lt;stdalign.h&gt;</code> in
17.14 <a href="https://wg21.link/support.runtime">[support.runtime]</a> p2 or upgrading to C11 as new base C standard.
</p>

<p><i>[2014-02-15 Issaquah]</i></p>

<p>
STL: related to earlier issue on C4, <a href="lwg-closed.html#2201" title="Missing macro entries from C standard library (Status: NAD Editorial)">2201</a><sup><a href="https://cplusplus.github.io/LWG/issue2201" title="Latest snapshot">(i)</a></sup>, and now we get a C11 header<br/>
JY: find _Alignof as keyword C11 FDIS has four defines in stdalign.h<br/>
AM: need paper for C11 as base library we should really do that<br/>
STL: really need vendor input<br/>
STL: don't think we need to do anything right now not P1<br/>
AM: any objections to downscale to P2  (no objections)
</p>

<p><i>[2016-03 Jacksonville]</i></p>

<p>
Walter: this is on track to go away if we adopt Clark's paper to rebase to C11<br/>
Room: tentatively resolved; revisit after C11 paper: <a href="https://wg21.link/P0063">P0063</a><br/>
</p>

<p><i>[2016-03 Oulu]</i></p>

<p><a href="https://wg21.link/P0063">P0063</a> was adopted.</p>
<p>Change status to Tentatively Resolved</p>


<p id="res-2241"><b>Proposed resolution:</b></p>





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