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<div class="identifier-type">function</div><div class="header"><debugging></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">is_debugger_present</span><span class="cpp cpp26" title="C++26で追加">(C++26)</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="k">namespace</span><span class="w"> </span><span class="nn">std</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="nf">is_debugger_present</span><span class="p">()</span><span class="w"> </span><span class="k">noexcept</span><span class="p">;</span><span class="w"> </span><span class="c1">// (1) C++26</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p>デバッガ実行中か判定する。</p>
<p>この関数は、デバッガがプログラムを監視中かどうかを判定する。プラットフォーム固有の結果を決定できない場合、ユーザーがこの関数を定義することで柔軟に動作を制御できる。</p>
<p>プログラムがデバッガ実行中かを判定できることで、デバッガ実行中に問題の診断に役立つ追加の出力やテストができる。</p>
<h2>置き換え可能</h2>
<p>ユーザーのプログラムでこの関数を定義することで、標準ライブラリで定義されるデフォルトの動作を置き換えることができる。</p>
<h2>要求される振る舞い</h2>
<ul>
<li>この関数は<a class="cpprefjp-defined-word" data-desc="関数等の意味論を構成する要素の1つ。Preconditions。関数呼び出し時に満たされていると関数が想定する条件。満たさなければ未定義の動作。契約属性の`[[expects]]`に相当">事前条件</a>をもたないこと</li>
</ul>
<h2>デフォルトの振る舞い</h2>
<ul>
<li><a class="cpprefjp-defined-word" data-desc="処理系定義の動作。処理系によって事前に定めた動作をする" href="../../implementation-compliance.html#dfn-implementation-defined-behavior">実装定義</a></li>
</ul>
<h2>効果</h2>
<p>デバッガがプログラムを監視中である場合、実装は<code>true</code>を返す。</p>
<h2><a class="cpprefjp-defined-word" data-desc="問題が発生したときに、現在実行位置を過去に通過・記録した位置に戻し、文脈情報を添えて紐づけられた処理(例外ハンドラー)を呼び出す仕組み。またはその事態">例外</a></h2>
<p>投げない</p>
<h2>備考</h2>
<ul>
<li>実装は、プログラムがデバッガによって監視されているかどうかを判定するために、必要に応じて即時クエリを実行する</li>
<li>Windowsまたは同等のシステムでは、この関数の動作はWin32関数の<code>::IsDebuggerPresent()</code>を呼び出すことで実現できる</li>
<li>POSIX環境では、監視親プロセスをチェックすることで実現できる。その際、監視親プロセスがデバッガであるかどうかは最善の努力で判定する</li>
<li>この関数は、結果のキャッシュを規定しない。既存の実装もデバッガの存在クエリについての結果をキャッシュするようなことはしておらず、そのコストが問題にはなっていなかった。また、結果をキャッシュする場合、<code><a href="breakpoint_if_debugging.html">std::breakpoint_if_debugging()</a></code>のインタフェースにも影響してしまう</li>
</ul>
<h2>例</h2>
<p><div class="yata" id="5be4cff8872d7d7ad8bf957e71b5995e603f3318"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../print.html"><print></a></span>
<span class="cp">#include <a href="../debugging.html"><debugging></a></span>
<span class="cp">#include <a href="../cmath.html"><cmath></a></span>
<span class="c1">// なんらかの処理</span>
<span class="kt">double</span><span class="w"> </span><span class="nf">g</span><span class="p">(</span><span class="kt">double</span><span class="w"> </span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="kt">double</span><span class="w"> </span><span class="n">b</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="n">b</span><span class="p">;</span>
<span class="p">}</span>
<span class="kt">double</span><span class="w"> </span><span class="nf">f</span><span class="p">(</span><span class="kt">double</span><span class="w"> </span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="kt">double</span><span class="w"> </span><span class="n">b</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">double</span><span class="w"> </span><span class="n">ret</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">g</span><span class="p">(</span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">);</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n"><a href="../cmath/isnan.html">std::isnan</a></span><span class="p">(</span><span class="n">ret</span><span class="p">)</span><span class="w"> </span><span class="o">||</span><span class="w"> </span><span class="n"><a href="../cmath/isinf.html">std::isinf</a></span><span class="p">(</span><span class="n">ret</span><span class="p">))</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">// 演算結果でNaNかinfが発生したらブレークし、</span>
<span class="w"> </span><span class="c1">// デバッガでパラメータ (ローカル変数) などを確認する</span>
<span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n"><span style="color:#ff0000">std::is_debugger_present</span></span><span class="p">())</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="breakpoint.html">std::breakpoint</a></span><span class="p">();</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="p">}</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">ret</span><span class="p">;</span>
<span class="p">}</span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">double</span><span class="w"> </span><span class="n">ret</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="mf">2.0</span><span class="p">,</span><span class="w"> </span><span class="mf">0.0</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../print/println.html">std::println</a></span><span class="p">(</span><span class="s">"{}"</span><span class="p">,</span><span class="w"> </span><span class="n">ret</span><span class="p">);</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h3>出力例</h3>
<p><pre><code>inf
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++26</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../implementation.html#clang">Clang</a>: 19 <span aria-label="未実装" role="img" title="未実装">❌</span></li>
<li><a href="../../implementation.html#gcc">GCC</a>: 14 <span aria-label="未実装" role="img" title="未実装">❌</span></li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: 2022 Update 10 <span aria-label="未実装" role="img" title="未実装">❌</span></li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="https://open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2546r5.html" target="_blank">P2546R5 Debugging Support</a></li>
<li><a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2810r4.html" target="_blank">P2810R4 <code>is_debugger_present is_replaceable</code></a></li>
</ul></div>
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