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‎reference/cstdlib.html‎

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<p class="text-right"><small>
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最終更新日時(UTC):
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<span itemprop="datePublished" content="2025-07-15T06:57:54">
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<span itemprop="datePublished" content="2025-12-02T04:14:25">
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@@ -505,7 +505,7 @@ <h2>マルチバイト文字とワイド文字の変換</h2>
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<td></td>
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<td><code>mblen</code></td>
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<td><code><a href="cstdlib/mblen.html">mblen</a></code></td>
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<td>マルチバイト文字の長さを取得する (function)</td>
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<td></td>
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‎reference/cstdlib/mblen.html‎

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2025年12月03日 00時51分04秒
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<span class="fa fa-fw fa-pencil"></span>編集
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<div class="identifier-type">function</div><div class="header">&lt;cstdlib&gt;</div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">mblen</span></h1>
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<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="k">namespace</span> <span class="n">std</span> <span class="p">{</span>
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<span class="kt">int</span> <span class="n">mblen</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span><span class="o">*</span> <span class="n">str</span><span class="p">,</span> <span class="kt">size_t</span> <span class="n">n</span><span class="p">);</span>
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<span class="p">}</span>
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</code></pre></div>
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</p>
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<h2>概要</h2>
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<p>マルチバイト文字列の先頭の文字が占めるバイト数を返す。</p>
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<p>先頭以外の文字に関するバイト数は計算されない。</p>
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<p>この関数は現在のロケールに依存してマルチバイト文字を解釈する。</p>
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<p><code>n</code>は解析に使用する最大バイト数を指定する。</p>
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<h2><a class="cpprefjp-defined-word" data-desc="関数呼び出し式の評価結果となるオブジェクト・値">戻り値</a></h2>
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<ul>
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<li>正常に動作する場合、文字の占めるバイト数を返す。</li>
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<li><code>str</code>が<code>nullptr</code>の時、内部状態を初期化し<code>0</code>を返す。</li>
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<li>無効な文字列、または<code>n</code>が不足している場合、<code>-1</code>を返す。</li>
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</ul>
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<h2>例</h2>
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<h3>基本的な使い方</h3>
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<p><div class="yata" id="09ad68cf80f1b31ea942f7955f5c148e8521c820"><div class="codehilite"><pre><span></span><code><span class="cp">#include</span> <span class="cpf"><a href="../iostream.html">&lt;iostream&gt;</a></span><span class="cp"></span>
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<span class="cp">#include</span> <span class="cpf"><a href="../cstdlib.html">&lt;cstdlib&gt;</a></span><span class="cp"></span>
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<span class="cp">#include</span> <span class="cpf">&lt;clocale&gt;</span><span class="cp"></span>
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<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
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<span class="n">std</span><span class="o">::</span><span class="n">setlocale</span><span class="p">(</span><span class="n">LC_ALL</span><span class="p">,</span> <span class="s">"ja_JP.UTF-8"</span><span class="p">);</span>
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<span class="k">const</span> <span class="kt">char</span> <span class="o">*</span><span class="n">str</span> <span class="o">=</span> <span class="s">"こんにちは"</span><span class="p">;</span>
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<span class="kt">int</span> <span class="n">result</span> <span class="o">=</span> <span class="n">std</span><span class="o">::</span><span class="n">mblen</span><span class="p">(</span><span class="n">str</span><span class="p">,</span> <span class="n">MB_CUR_MAX</span><span class="p">);</span>
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<span class="n"><a href="../iostream/cout.html">std::cout</a></span> <span class="o">&lt;&lt;</span> <span class="n">result</span> <span class="o">&lt;&lt;</span> <span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
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<span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
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<span class="p">}</span>
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</code></pre></div>
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</div></p>
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<h4>出力例</h4>
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<p><pre><code>3
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</code></pre></p>
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<h3>文字列の文字数を計算する</h3>
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<p><div class="yata" id="ab1990ecb189149772909ce3d4b8510a55045092"><div class="codehilite"><pre><span></span><code><span class="cp">#include</span> <span class="cpf"><a href="../iostream.html">&lt;iostream&gt;</a></span><span class="cp"></span>
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<span class="cp">#include</span> <span class="cpf"><a href="../cstdlib.html">&lt;cstdlib&gt;</a></span><span class="cp"></span>
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<span class="cp">#include</span> <span class="cpf">&lt;clocale&gt;</span><span class="cp"></span>
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<span class="kt">int</span> <span class="nf">count_chars_mblen</span><span class="p">(</span><span class="k">const</span> <span class="kt">char</span><span class="o">*</span> <span class="n">s</span><span class="p">)</span> <span class="p">{</span>
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<span class="n">std</span><span class="o">::</span><span class="n">setlocale</span><span class="p">(</span><span class="n">LC_ALL</span><span class="p">,</span> <span class="s">"ja_JP.UTF-8"</span><span class="p">);</span>
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<span class="kt">int</span> <span class="n">count</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
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<span class="kt">size_t</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
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<span class="k">while</span> <span class="p">(</span><span class="n">s</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">!=</span> <span class="sc">'\0'</span><span class="p">)</span> <span class="p">{</span>
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<span class="kt">int</span> <span class="n">len</span> <span class="o">=</span> <span class="n">std</span><span class="o">::</span><span class="n">mblen</span><span class="p">(</span><span class="o">&amp;</span><span class="n">s</span><span class="p">[</span><span class="n">i</span><span class="p">],</span> <span class="n">MB_CUR_MAX</span><span class="p">);</span>
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<span class="k">if</span> <span class="p">(</span><span class="n">len</span> <span class="o">&lt;</span> <span class="mi">0</span><span class="p">)</span> <span class="p">{</span>
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<span class="n">len</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="n">i</span> <span class="o">+=</span> <span class="n">len</span><span class="p">;</span>
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<span class="n">count</span><span class="o">++</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="k">return</span> <span class="n">count</span><span class="p">;</span>
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<span class="p">}</span>
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<span class="kt">int</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
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<span class="k">const</span> <span class="kt">char</span><span class="o">*</span> <span class="n">str</span> <span class="o">=</span> <span class="s">"こんにちは世界"</span><span class="p">;</span>
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<span class="n"><a href="../iostream/cout.html">std::cout</a></span> <span class="o">&lt;&lt;</span> <span class="s">"文字列: "</span> <span class="o">&lt;&lt;</span> <span class="n">str</span> <span class="o">&lt;&lt;</span> <span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span>
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<span class="n"><a href="../iostream/cout.html">std::cout</a></span> <span class="o">&lt;&lt;</span> <span class="s">"文字数: "</span> <span class="o">&lt;&lt;</span> <span class="n">count_chars_mblen</span><span class="p">(</span><span class="n">str</span><span class="p">)</span> <span class="o">&lt;&lt;</span> <span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span>
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<span class="p">}</span>
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</code></pre></div>
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</div></p>
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<h4>出力例</h4>
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<p><pre><code>文字列: こんにちは世界
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文字数: 7
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</code></pre></p></div>
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