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<title>Issue 879: Atomic load const qualification</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_Editorial">NAD Editorial</a> status.</em></p>
<h3 id="879"><a href="lwg-closed.html#879">879</a>. Atomic load const qualification</h3>
<p><b>Section:</b> 32.5 <a href="https://wg21.link/atomics">[atomics]</a> <b>Status:</b> <a href="lwg-active.html#NAD_Editorial">NAD Editorial</a>
 <b>Submitter:</b> Alexander Chemeris <b>Opened:</b> 2008-08-24 <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#atomics">issues</a> in [atomics].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The <code>atomic_address</code> type and <code>atomic&lt;T*&gt;</code> specialization provide atomic
updates to pointers.  However, the current specification requires
that the types pointer be to non-const objects.  This restriction
is unnecessary and unintended.
</p>

<p><i>[
Summit:
]</i></p>

<blockquote><p>
Move to review.  Lawrence will first check with Peter whether the
current examples are sufficient, or whether they need to be expanded to
include all cases.
</p></blockquote>

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


<blockquote>
<p>
Lawrence will handle all issues relating to atomics in a single paper.
</p>
<p>
LWG will defer discussion on atomics until that paper appears.
</p>
<p>
Move to Open.
</p>
</blockquote>

<p><i>[
2009-08-17 Handled by
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2925.html">N2925</a>.
]</i></p>


<p><i>[
2009-10 Santa Cruz:
]</i></p>


<blockquote><p>
NAD Editorial.  Solved by
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2992.htm">N2992</a>.
</p></blockquote>



<p id="res-879"><b>Proposed resolution:</b></p>
<p>
Add const qualification to the pointer values of the <code>atomic_address</code>
and <code>atomic&lt;T*&gt;</code> specializations.  E.g.
</p>

<blockquote><pre>
typedef struct atomic_address {
   void store(<ins>const</ins> void*, memory_order = memory_order_seq_cst) volatile;
   void* exchange( <ins>const</ins> void*, memory_order = memory_order_seq_cst) volatile;
   bool compare_exchange( <ins>const</ins> void*&amp;, <ins>const</ins> void*,
                          memory_order, memory_order) volatile;
   bool compare_exchange( <ins>const</ins> void*&amp;, <ins>const</ins> void*,
                          memory_order = memory_order_seq_cst ) volatile;
   void* operator=(<ins>const</ins> void*) volatile;
} atomic_address;

void atomic_store(volatile atomic_address*, <ins>const</ins> void*);
void atomic_store_explicit(volatile atomic_address*, <ins>const</ins> void*,
                          memory_order);
void* atomic_exchange(volatile atomic_address*<ins>, const void*</ins>);
void* atomic_exchange_explicit(volatile atomic_address*, <ins>const</ins> void*,
                              memory_order);
bool atomic_compare_exchange(volatile atomic_address*,
                            <ins>const</ins> void**, <ins>const</ins> void*);
bool atomic_compare_exchange_explicit(volatile atomic_address*,
                                     <ins>const</ins> void**, <ins>const</ins> void*,
                                     memory_order, memory_order);
</pre></blockquote>





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