devdocs/c/atomic%2Fatomic_flag_test_and_set.html


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    <h1 id="firstHeading" class="firstHeading">atomic_flag_test_and_set, atomic_flag_test_and_set_explicit</h1>            <table class="t-dcl-begin"> <tr class="t-dsc-header"> <th> Defined in header <code>&lt;stdatomic.h&gt;</code> </th> <th> </th> <th> </th> </tr> <tr class="t-dcl t-since-c11"> <td> <pre data-language="c">_Bool atomic_flag_test_and_set( volatile atomic_flag* obj );</pre>
</td> <td> (1) </td> <td> <span class="t-mark-rev t-since-c11">(since C11)</span> </td> </tr> <tr class="t-dcl t-since-c11"> <td> <pre data-language="c">_Bool atomic_flag_test_and_set_explicit( volatile atomic_flag* obj, memory_order order );</pre>
</td> <td> (2) </td> <td> <span class="t-mark-rev t-since-c11">(since C11)</span> </td> </tr>  </table> <p>Atomically changes the state of a <code>atomic_flag</code> pointed to by <code>obj</code> to set (<code>true</code>) and returns the previous value. The first version orders memory accesses according to <code><a href="memory_order" title="c/atomic/memory order">memory_order_seq_cst</a></code>, the second version orders memory accesses according to <code>order</code>.</p>
<p>The argument is pointer to a volatile atomic flag to accept addresses of both non-volatile and <a href="../language/volatile" title="c/language/volatile">volatile</a> (e.g. memory-mapped I/O) atomic flags.</p>
<h3 id="Parameters"> Parameters</h3> <table class="t-par-begin"> <tr class="t-par"> <td> obj </td> <td> - </td> <td> pointer to the atomic flag object to modify </td>
</tr> <tr class="t-par"> <td> order </td> <td> - </td> <td> the memory synchronization ordering for this operation: all values are permitted </td>
</tr>
</table> <h3 id="Return_value"> Return value</h3> <p>The previous value held by the atomic flag pointed to by <code>obj</code>.</p>
<h3 id="References"> References</h3>  <ul>
<li> C17 standard (ISO/IEC 9899:2018): </li>
<ul><li> 7.17.8.1 The atomic_flag_test_and_set functions (p: 209) </li></ul>
<li> C11 standard (ISO/IEC 9899:2011): </li>
<ul><li> 7.17.8.1 The atomic_flag_test_and_set functions (p: 285-286) </li></ul>
</ul>       <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td> <div><a href="atomic_flag_clear" title="c/atomic/atomic flag clear"> <span class="t-lines"><span>atomic_flag_clear</span><span>atomic_flag_clear_explicit</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c11">(C11)</span></span></span></div> </td> <td> sets an atomic_flag to false <br> <span class="t-mark">(function)</span>  </td>
</tr> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/atomic/atomic_flag_test_and_set" title="cpp/atomic/atomic flag test and set">C++ documentation</a></span> for <code>atomic_flag_test_and_set, atomic_flag_test_and_set_explicit</code> </td>
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