148 lines
8.6 KiB
HTML
148 lines
8.6 KiB
HTML
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<title>std::memset</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_string_byte_memset skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>memset</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-string.html">string</a>‎ | <a href="cpp-string-byte.html">byte</a></span></div>
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<td>
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<div>定义于头文件 <code><a href="cpp-header-cstring.html"><cstring></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span> memset<span class="br0">(</span> <span class="kw4">void</span><span class="sy2">*</span> dest, <span class="kw4">int</span> ch, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> count <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>转换值 <code>ch</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">char</span></span></span> 并复制它到 <code>dest</code> 所指向对象的首 <code>count</code> 个字节。若该对象是<a href="cpp-language-object.html#.E5.AD.90.E5.AF.B9.E8.B1.A1">潜在重叠的子对象</a>或非 <a href="cpp-named_req-TriviallyCopyable.html"><span style="font-style:italic">可平凡复制</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(TriviallyCopyable)</span></a> （例如标量、 C 兼容的结构体或可平凡复制类型的数组），则行为未定义。若 <code>count</code> 大于 <code>dest</code> 所指向的对象大小，则行为未定义。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>dest</td>
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<td>-</td>
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<td>指向要填充的对象的指针</td>
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</tr>
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<tr class="t-par">
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<td>ch</td>
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<td>-</td>
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<td>填充字节</td>
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</tr>
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<tr class="t-par">
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<td>count</td>
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<td>-</td>
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<td>要填充的字节数</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p><code>dest</code></p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>若 <code>std::memset</code> 所修改的对象在其生存期的剩余部分不再被访问，则此函数可以被优化掉（在<a href="cpp-language-as_if.html">如同</a>规则下）（例如 <a rel="nofollow" class="external text" href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=8537">gcc 漏洞 8537</a> ）。为此，此函数不能用于擦洗内存（例如以令填充存储密码的数组）。该问题的解决方案包含 C11 <a href="c-string-byte-memset.html"><tt>memset_s</tt></a> 、 FreeBSD <a rel="nofollow" class="external text" href="https://www.freebsd.org/cgi/man.cgi?query=explicit_bzero">explicit_bzero</a> 或 Microsoft <a rel="nofollow" class="external text" href="https://msdn.microsoft.com/en-us/library/windows/desktop/aa366877.aspx">SecureZeroMemory</a> 。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <cstring></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">int</span> a<span class="br0">[</span><span class="nu0">20</span><span class="br0">]</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">memset</span><span class="br0">(</span>a, <span class="nu0">0</span>, sizeof a<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> ai <span class="sy4">:</span> a<span class="br0">)</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> ai<span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">00000000000000000000</pre></div>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-byte-memcpy.html"><span class="t-lines"><span>memcpy</span></span></a></div>
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</div>
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</td>
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<td>复制一个缓冲区到另一个<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-byte-memmove.html"><span class="t-lines"><span>memmove</span></span></a></div>
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</div>
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</td>
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<td>移动一个缓冲区到另一个<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-wide-wmemset.html"><span class="t-lines"><span>wmemset</span></span></a></div>
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</div>
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</td>
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<td>复制给定宽字符到宽字符数组的每个位置<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-fill.html"><span class="t-lines"><span>fill</span></span></a></div>
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</div>
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</td>
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<td>将一个给定值复制赋值给一个范围内的每个元素<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-fill_n.html"><span class="t-lines"><span>fill_n</span></span></a></div>
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</div>
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</td>
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<td>将一个给定值复制赋值给一个范围内的 N 个元素<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-types-is_trivially_copyable.html"><span class="t-lines"><span>is_trivially_copyable</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>检查类型是否可平凡复制<br />
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<span class="t-mark">(类模板)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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