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<div class="identifier-type">class template</div><div class="header"><codecvt></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">codecvt_utf8</span><span class="cpp cpp11" title="C++11で追加">(C++11)</span><span class="cpp cpp17deprecated text-warning" title="C++17で非推奨">(C++17で非推奨)</span><span class="cpp cpp26removed text-danger" title="C++26で削除">(C++26で削除)</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="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">Elem</span><span class="p">,</span><span class="w"> </span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">long</span><span class="w"> </span><span class="n">Maxcode</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mh">0x10ffff</span><span class="p">,</span>
<span class="w"> </span><span class="n"><a href="codecvt_mode.html">codecvt_mode</a></span><span class="w"> </span><span class="n">Mode</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">(</span><span class="n"><a href="codecvt_mode.html">codecvt_mode</a></span><span class="p">)</span><span class="mi">0</span><span class="o">></span>
<span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">codecvt_utf8</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="k">public</span><span class="w"> </span><span class="n"><a href="../locale/codecvt.html">codecvt</a></span><span class="o"><</span><span class="n">Elem</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="p">,</span><span class="w"> </span><span class="kt">mbstate_t</span><span class="o">></span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">// 未規定...</span>
<span class="w"> </span><span class="p">};</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p>UTF-8との変換を行うファセットクラス。<code>char</code>列と<code>Elem</code>列との間で、以下のようにエンコーディングの変換を行う機能を有する。</p>
<ul>
<li><code>char</code>: UTF-8エンコーディングのマルチバイト文字列。</li>
<li><code>Elem</code>: UCS-2またはUCS-4 (UTF-32)。<code>char16_t</code>など2バイトの型を指定するとUCS-2、<code>char32_t</code>など4バイトの型を指定するとUCS-4として扱われる。</li>
</ul>
<p>BOMの有無を<code><a href="codecvt_mode.html">codecvt_mode</a></code>で指定できる。</p>
<h2>非推奨・削除の詳細</h2>
<p>Unicodeの文字コード変換を行うこれらのクラスは、不正なコードポイントに対する安全なエラー処理の方法を提供していなかったため、セキュリティ上の欠陥があった。</p>
<p>仕様もあいまいであったため、不正なコードポイントに対してどのように振る舞うかも不明であった。</p>
<p>Unicode以外のShift_JISやBig5といった文字コードの利用が急激に減少している。標準ライブラリでの現代的なUnicodeの変換機能は非常に必要とされているが、<code><codecvt></code>の設計はお粗末なものだった。将来より良いものを作るために、これらの機能は非推奨・削除とする。</p>
<p>標準ライブラリにUnicodeの文字コード変換をする代替機能はないため、他の専門特化した文字コード変換のライブラリを使用すること。</p>
<h2>例</h2>
<p><div class="yata" id="be699520e1628c78a3bf19654cd3cd42a87482ba"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../codecvt.html"><codecvt></a></span>
<span class="cp">#include <a href="../string.html"><string></a></span>
<span class="cp">#include <a href="../cassert.html"><cassert></a></span>
<span class="cp">#include <a href="../locale.html"><locale></a></span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../locale/wstring_convert.html">std::wstring_convert</a></span><span class="o"><</span><span class="n"><span style="color:#ff0000">std::codecvt_utf8</span></span><span class="o"><</span><span class="kt">char32_t</span><span class="o">></span><span class="p">,</span><span class="w"> </span><span class="kt">char32_t</span><span class="o">></span><span class="w"> </span><span class="n">converter</span><span class="p">;</span>
<span class="w"> </span><span class="c1">// UCS-4/UTF-32からUTF-8に変換</span>
<span class="w"> </span><span class="n"><a href="../string/basic_string.html">std::u32string</a></span><span class="w"> </span><span class="n">u32str</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sa">U</span><span class="s">"</span><span class="se">\U0001F359</span><span class="s">"</span><span class="p">;</span>
<span class="w"> </span><span class="n"><a href="../string/basic_string.html">std::string</a></span><span class="w"> </span><span class="n">u8str</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../locale/wstring_convert/to_bytes.html">converter.to_bytes</a></span><span class="p">(</span><span class="n">u32str</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="../string/basic_string/size.html">u8str.size()</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="mi">4</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="../string/basic_string/op_at.html">u8str[0]</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">'\xf0'</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="../string/basic_string/op_at.html">u8str[1]</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">'\x9f'</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="../string/basic_string/op_at.html">u8str[2]</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">'\x8d'</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n"><a href="../string/basic_string/op_at.html">u8str[3]</a></span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="sc">'\x99'</span><span class="p">);</span>
<span class="w"> </span><span class="c1">// UTF-8からUCS-4/UTF-32に変換</span>
<span class="w"> </span><span class="n"><a href="../string/basic_string.html">std::u32string</a></span><span class="w"> </span><span class="n">restored</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../locale/wstring_convert/from_bytes.html">converter.from_bytes</a></span><span class="p">(</span><span class="n">u8str</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../cassert/assert.html">assert</a></span><span class="p">(</span><span class="n">u32str</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">restored</span><span class="p">);</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h3>出力</h3>
<p>上記プログラムは何も出力しない。</p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++11</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../implementation.html#clang">Clang</a>: 3.0 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../implementation.html#gcc">GCC</a>: 5.1 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../implementation.html#icc">ICC</a>: ?</li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: 2010 <span aria-label="検証済" role="img" title="検証済">✅</span>, 2012 <span aria-label="検証済" role="img" title="検証済">✅</span>, 2013 <span aria-label="検証済" role="img" title="検証済">✅</span>, 2015 <span aria-label="検証済" role="img" title="検証済">✅</span>, 2017 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2401.htm" target="_blank">N2401 Code Conversion Facets for the Standard C++ Library</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0618r0.html" target="_blank">P0618R0 Deprecating <code><codecvt></code></a></li>
<li><a href="https://open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2871r3.pdf" target="_blank">P2871R3 Remove Deprecated Unicode Conversion Facets from C++26</a></li>
</ul></div>
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