75 lines
6.1 KiB
HTML
75 lines
6.1 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>文件名和行信息</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-cpp_preprocessor_line 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">文件名和行信息</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-preprocessor.html">preprocessor</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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<p>更改预处理器中当前的行号和文件名。</p>
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<h3><span class="mw-headline" id=".E8.AF.AD.E6.B3.95">语法</span></h3>
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<table class="t-sdsc-begin">
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><code><b>#line</b></code> <span class="t-spar">行号</span></td>
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<td>(1)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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<tr class="t-sdsc">
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<td><code><b>#line</b></code> <span class="t-spar">行号</span> <code><b>"</b></code><span class="t-spar">文件名</span><code><b>"</b></code></td>
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<td>(2)</td>
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<td class="t-sdsc-nopad"></td>
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</tr>
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<tr>
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<td colspan="10" class="t-sdsc-sep"></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
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<p>1) 将当前的预处理器行号更改为 <span class="t-spar">行号</span>。宏 <span class="t-c"><span class="mw-geshi cpp source-cpp">__LINE__</span></span> 在该点后的展开将产生 <span class="t-spar">行号</span> 加上自此遇到的实际代码行数。</p>
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<p>2) 还将当前的预处理器文件名更改为 <span class="t-spar">文件名</span>。宏 <span class="t-c"><span class="mw-geshi cpp source-cpp">__FILE__</span></span> 在该点后的展开将生成 <span class="t-spar">文件名</span>。</p>
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<p>任何预处理器记号（宏常量或表达式）都允许作为 <code>#line</code> 的实参，只要它们展开成合法的十进制整数，可选地后随一个合法的字符串即可。</p>
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<p><span class="t-spar">行号</span> 必须是至少有一个十进制位的序列（否则程序非良构），并且始终按十进制解释（即使它以 <code>0</code> 开始也是如此）。</p>
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<p>若 <span class="t-spar">行号</span> 为 0 或大于 <span class="t-rev-inl t-until-cxx11"><span>32767</span> <span><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></span></span><span class="t-rev-inl t-since-cxx11"><span>2147483647</span> <span><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></span></span>，则行为未定义。</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>一些自动代码生成工具通过以其他语言编写的文件产生 C++ 源文件时，会使用此指令。这种情况下，它们在所生成的 C++ 文件中插入 <code>#line</code> 指令，以指代原（人类编辑的）源文件的行号和文件名。</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 <cassert></span>
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<span class="co2">#define FNAME "test.cc"</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="co2">#line 777 FNAME</span>
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<a href="cpp-error-assert.html"><span class="kw774">assert</span></a><span class="br0">(</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="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">test: test.cc:777: int main(): Assertion `2+2 == 5' failed.</pre></div>
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</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"></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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</div>
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</body>
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</html>
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