102 lines
6.5 KiB
HTML
102 lines
6.5 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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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>std::difftime</title>
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<link rel="stylesheet" href="ext.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_chrono_c_difftime 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"><span style="font-size:0.7em; line-height:130%">std::</span>difftime</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-chrono.html">chrono</a>‎ | <a href="cpp-chrono-c.html">c</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><a href="cpp-header-ctime.html"><ctime></a></code></div>
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</td>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span> difftime<span class="br0">(</span> <a href="cpp-chrono-c-time_t.html"><span class="kw1023">std::<span class="me2">time_t</span></span></a> time_end, <a href="cpp-chrono-c-time_t.html"><span class="kw1023">std::<span class="me2">time_t</span></span></a> time_beg <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></td>
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<p>以秒计算二个作为 <span class="t-lc"><a href="cpp-chrono-c-time_t.html">std::time_t</a></span> 对象的日历时间差（ <span class="t-c"><span class="mw-geshi cpp source-cpp">time_end <span class="sy2">-</span> time_beg</span></span> ）。若 <code>time_end</code> 指代 <code>time_beg</code> 之前的时间点，则结果为负。</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>time_beg, time_end</td>
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<td>-</td>
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<td>要比较的时间</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>以秒表示的二个时间的差。</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>POSIX 系统上， <span class="t-lc"><a href="cpp-chrono-c-time_t.html">std::time_t</a></span> 以秒度量，而 <code>difftime</code> 等价于算术减法，但 C 和 C++ 允许 <code>time_t</code> 有分数单位。</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 <ctime></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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<a href="cpp-chrono-c-time_t.html"><span class="kw1023">std::<span class="me2">time_t</span></span></a> start <span class="sy1">=</span> <a href="cpp-chrono-c-time.html"><span class="kw1010">std::<span class="me2">time</span></span></a><span class="br0">(</span><a href="cpp-types-NULL.html"><span class="kw103">NULL</span></a><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">volatile</span> <span class="kw4">double</span> d<span class="sy4">;</span>
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<span class="co1">// 一些耗时操作</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> n<span class="sy1">=</span><span class="nu0">0</span><span class="sy4">;</span> n<span class="sy1"><</span><span class="nu0">10000</span><span class="sy4">;</span> <span class="sy2">++</span>n<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> m<span class="sy1">=</span><span class="nu0">0</span><span class="sy4">;</span> m<span class="sy1"><</span><span class="nu0">100000</span><span class="sy4">;</span> <span class="sy2">++</span>m<span class="br0">)</span> <span class="br0">{</span>
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d <span class="sy2">+</span><span class="sy1">=</span> d<span class="sy2">*</span>n<span class="sy2">*</span>m<span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Wall time passed: "</span>
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<span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">difftime</span><span class="br0">(</span><a href="cpp-chrono-c-time.html"><span class="kw1010">std::<span class="me2">time</span></span></a><span class="br0">(</span><a href="cpp-types-NULL.html"><span class="kw103">NULL</span></a><span class="br0">)</span>, start<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" s.<span class="es1">\n</span>"</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">Wall time passed: 7 s.</pre></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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<div class="t-dsc-member-div">
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<div><a href="cpp-chrono-duration.html"><span class="t-lines"><span>duration</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>时间区间<br />
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<span class="t-mark">(类模板)</span></td>
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