172 lines
7.2 KiB
HTML
172 lines
7.2 KiB
HTML
<!DOCTYPE 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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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>va_start</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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</head>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_variadic_va_start skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading">va_start</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="c.html">c</a>‎ | <a href="c-variadic.html">variadic</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<table class="t-dcl-begin">
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<tbody>
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<td>
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<div>定义于头文件 <code><stdarg.h></code></div>
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</td>
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<td></td>
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<td></td>
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</tr>
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<tr class="t-dcl">
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<div><span class="mw-geshi c source-c"><span class="kw4">void</span> va_start<span class="br0">(</span> va_list ap, parmN <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td class="t-dcl-nopad"></td>
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<td class="t-dcl-nopad"></td>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p><code>va_start</code> 宏使函数能访问<code>parmN</code>后的可变参数。</p>
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<p>应该在任何对 <span class="t-lc">va_arg</span> 的调用前,以合法的 <span class="t-lc">va_list</span> 对象 <code>ap</code> 调用 <code>va_start</code> 。</p>
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<p>若 <code>parmN</code> 声明带有 <code>register</code> 存储类指定符、数组类型、函数类型,或与默认参数提升结果类型不兼容的类型,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>ap</td>
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<td>-</td>
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<td><span class="t-lc">va_list</span> 类型实例</td>
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</tr>
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<tr class="t-par">
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<td>parmN</td>
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<td>-</td>
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<td>首个可变参数前的参数名</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.B1.95.E5.BC.80.E5.80.BC">展开值</span></h3>
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<p>(无)</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="c source-c">
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<pre class="de1"><span class="co2">#include <stdio.h></span>
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<span class="co2">#include <stdarg.h></span>
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<span class="kw4">int</span> add_nums<span class="br0">(</span><span class="kw4">int</span> count, ...<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">int</span> result <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
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va_list args<span class="sy4">;</span>
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va_start<span class="br0">(</span>args, count<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> i <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> i <span class="sy1"><</span> count<span class="sy4">;</span> <span class="sy2">++</span>i<span class="br0">)</span> <span class="br0">{</span>
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result <span class="sy2">+</span><span class="sy1">=</span> va_arg<span class="br0">(</span>args, <span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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va_end<span class="br0">(</span>args<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> result<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="c-io-fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%d<span class="es1">\n</span>"</span>, add_nums<span class="br0">(</span><span class="nu0">4</span>, <span class="nu0">25</span>, <span class="nu0">25</span>, <span class="nu0">50</span>, <span class="nu0">50</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>可能的输出:</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">150</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
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<div class="t-ref-std-11">
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<ul>
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<li>C11 标准(ISO/IEC 9899:2011):</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.16.1.4 The va_start macro (p: 271-272)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c99">
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<ul>
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<li>C99 标准(ISO/IEC 9899:1999):</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.15.1.4 The va_start macro (p: 251-252)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c89">
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<ul>
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<li>C89/C90 标准(ISO/IEC 9899:1990):</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>4.8.1.1 The va_start macro</li>
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</ul>
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</dd>
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</dl>
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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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<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="c-variadic-va_arg.html"><span class="t-lines"><span>va_arg</span></span></a></div>
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</div>
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</td>
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<td>访问下一个函数可变参数<br />
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<span class="t-mark">(宏函数)</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="c-variadic-va_copy.html"><span class="t-lines"><span>va_copy</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div>
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</div>
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</td>
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<td>创造函数可变参数的副本<br />
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<span class="t-mark">(宏函数)</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="c-variadic-va_end.html"><span class="t-lines"><span>va_end</span></span></a></div>
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</div>
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</td>
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<td>结束函数可变参数的行程<br />
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<span class="t-mark">(宏函数)</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="c-variadic-va_list.html"><span class="t-lines"><span>va_list</span></span></a></div>
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</div>
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</td>
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<td>保有 va_start 、 va_arg 、 va_end 及 va_copy 所需信息<br />
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<span class="t-mark">(typedef)</span></td>
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</tr>
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</table>
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</div>
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</div>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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