161 lines
8.4 KiB
HTML
161 lines
8.4 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>assert</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_error_assert 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">assert</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-error.html">error</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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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><assert.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 class="t-dcl">
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<div><span class="mw-geshi c source-c"><span class="co2">#ifdef NDEBUG</span><br /></span>
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<p><span class="co2">#define assert(condition) ((void)0)</span><br />
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<span class="co2">#else</span><br />
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<span class="co2">#define assert(condition) /*implementation defined*/</span><br /></p>
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<span class="co2">#endif</span></div>
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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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<p>宏 <code>assert</code> 的定义依赖于标准库不定义的另一个宏 <span class="t-c"><span class="mw-geshi c source-c">NDEBUG</span></span> 。</p>
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<p>若 <span class="t-c"><span class="mw-geshi c source-c">NDEBUG</span></span> 在包含了 <code><assert.h></code> 的源代码中的点定义为宏名，则 <code>assert</code> 不做任何事。</p>
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<p>若不定义 <span class="t-c"><span class="mw-geshi c source-c">NDEBUG</span></span> ，则 <code>assert</code> 将其参数（必须拥有标量类型）与零比较相等。若相等，则 <code>assert</code> 在标准错误输出上输出实现指定的诊断信息，并调用 <span class="t-c"><span class="mw-geshi c source-c"><a href="c-program-abort.html"><span class="kw486">abort</span></a><span class="br0">(</span><span class="br0">)</span></span></span> 。诊断信息要求包含表达式的文本，还有<span class="t-rev-inl t-since-c99"><span><a href="c-language-function_definition.html">预定义变量</a> <span class="t-c"><span class="mw-geshi c source-c">__func__</span></span> 与</span> <span><span class="t-mark-rev t-since-c99">(C99 起)</span></span></span><a href="c-preprocessor-replace.html">预定义宏</a> <span class="t-c"><span class="mw-geshi c source-c">__FILE__</span></span>、 <span class="t-c"><span class="mw-geshi c source-c">__LINE__</span></span> 的值。</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>condition</td>
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<td>-</td>
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<td>标量类型表达式</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>（无）</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>没有标准化的添加消息到 <code>assert</code> 错误的接口。一个包含它的方式是使用<a href="c-language-operator_other.html#.E9.80.97.E5.8F.B7.E8.BF.90.E7.AE.97.E7.AC.A6">逗号运算符</a>：</p>
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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">assert<span class="br0">(</span><span class="br0">(</span><span class="st0">"There are five lights"</span>, <span class="nu0">2</span> <span class="sy2">+</span> <span class="nu0">2</span> <span class="sy1">==</span> <span class="nu0">5</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span></pre></div>
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</div>
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<p><code>assert</code> 在 <a rel="nofollow" class="external text" href="https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/assert-macro-assert-wassert?view=msvc-160">Microsoft CRT</a> 中的实现不遵从 C99 以及后续标准版本，因为其底层函数 ( <code>_wassert</code> ）不接收 <span class="t-c"><span class="mw-geshi c source-c">__func__</span></span> 或等价的替代品。</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="co1">// 反注释可禁用 assert()</span>
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<span class="co1">// #define NDEBUG</span>
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<span class="co2">#include <assert.h></span>
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<span class="co2">#include <math.h></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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<span class="kw4">double</span> x <span class="sy1">=</span> <span class="sy2">-</span><span class="nu16">1.0</span><span class="sy4">;</span>
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assert<span class="br0">(</span>x <span class="sy1">>=</span> <span class="nu16">0.0</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"sqrt(x) = %f<span class="es1">\n</span>"</span>, <a href="c-numeric-math-sqrt.html"><span class="kw664">sqrt</span></a><span class="br0">(</span>x<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> <span class="nu0">0</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>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">output with NDEBUG not defined:
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a.out: main.cpp:10: main: Assertion `x >= 0.0' failed.
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output with NDEBUG defined:
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sqrt(x) = -nan</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-17">
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<ul>
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<li>C17 标准（ISO/IEC 9899:2018）：</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>7.2.1.1 The assert macro (p: 135)</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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<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>7.2.1.1 The assert macro (p: 186-187)</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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<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>7.2.1.1 The assert macro (p: 169)</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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<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>4.2.1.1 The assert 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-program-abort.html"><span class="t-lines"><span>abort</span></span></a></div>
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</div>
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</td>
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<td>引发非正常的程序终止（不清理）<br />
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<span class="t-mark">(函数)</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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</div>
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</div>
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</body>
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