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authorCraig Jennings <c@cjennings.net>2024-04-07 13:41:34 -0500
committerCraig Jennings <c@cjennings.net>2024-04-07 13:41:34 -0500
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+ <h1 id="firstHeading" class="firstHeading">C attribute: maybe_unused <span class="t-mark-rev t-since-c23">(since C23)</span>
+</h1> <p>Suppresses warnings on unused entities.</p>
+<h3 id="Syntax"> Syntax</h3> <table class="t-sdsc-begin"> <tr class="t-sdsc"> <td class="t-sdsc-nopad"> <code>[[</code> <code>maybe_unused</code> <code>]]</code><br><code>[[</code> <code>__maybe_unused__</code> <code>]]</code> </td> <td class="t-sdsc-nopad"> </td> <td class="t-sdsc-nopad"> </td>
+</tr>
+</table> <h3 id="Explanation"> Explanation</h3> <p>This attribute can appear in the declaration of the following entities:</p>
+<ul>
+<li> <a href="../struct" title="c/language/struct">struct</a>/<a href="../union" title="c/language/union">union</a>: <code>struct [[maybe_unused]] S;</code>, </li>
+<li> <a href="../typedef" title="c/language/typedef">typedef name</a>: <code>[[maybe_unused]] typedef S* PS;</code>, </li>
+<li> object: <code>[[maybe_unused]] int x;</code>, </li>
+<li> struct/union member: <code>union U { [[maybe_unused]] int n; };</code>, </li>
+<li> <a href="../function_definition" title="c/language/function definition">function</a>: <code>[[maybe_unused]] void f(void);</code>, </li>
+<li> <a href="../enum" title="c/language/enum">enumeration</a>: <code>enum [[maybe_unused]] E {};</code>, </li>
+<li> enumerator: <code>enum { A [[maybe_unused]], B [[maybe_unused]] = 42 };</code>. </li>
+</ul> <p>If the compiler issues warnings on unused entities, that warning is suppressed for any entity declared <code>maybe_unused</code>.</p>
+<h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#include &lt;assert.h&gt;
+
+[[maybe_unused]] void f([[maybe_unused]] _Bool cond1, [[maybe_unused]] _Bool cond2)
+{
+ [[maybe_unused]] _Bool b = cond1 &amp;&amp; cond2;
+ assert(b); // in release mode, assert is compiled out, and b is unused
+ // no warning because it is declared [[maybe_unused]]
+} // parameters cond1 and cond2 are not used, no warning
+
+int main(void)
+{
+ f(1, 1);
+}</pre></div> </div> <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/language/attributes/maybe_unused" title="cpp/language/attributes/maybe unused">C++ documentation</a></span> for <code>maybe_unused</code> </td>
+</tr> </table> <div class="_attribution">
+ <p class="_attribution-p">
+ &copy; cppreference.com<br>Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.<br>
+ <a href="https://en.cppreference.com/w/c/language/attributes/maybe_unused" class="_attribution-link">https://en.cppreference.com/w/c/language/attributes/maybe_unused</a>
+ </p>
+</div>