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<!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>clock</title>
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<link rel="stylesheet" href="site_modules.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_chrono_clock 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">clock</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-chrono.html">chrono</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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<td>
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<div>定义于头文件 <code><time.h></code></div>
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<td></td>
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<td></td>
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<div><span class="mw-geshi c source-c"><a href="c-chrono-clock_t.html"><span class="kw524">clock_t</span></a> clock<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>返回从关联到进程开始执行的实现定义时期的起，进程所用的粗略处理器时间。将此值除以 <span class="t-lc"><a href="c-chrono-CLOCKS_PER_SEC.html">CLOCKS_PER_SEC</a></span> 可转换为秒。</p>
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<p>只有两次对 <code>clock</code> 不同调用的返回值的差是有意义的，因为 <code>clock</code> 时期的起始不必与程序起始一致。 <code>clock</code> 时间或许会快于或慢于挂钟时间，这取决于操作系统给予程序的执行资源。例如，若 CPU 为其他进程所共享， <code>clock</code> 时间可能慢于挂钟。另一方面，若当前进程为多线程，而有更多资源可用， <code>clock</code> 时间可能会快于挂钟。</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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<p>（无）</p>
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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>程序迄今为止所用的处理器时间。若该信息不可用，或若其值无法表示，则为 <span class="t-c"><span class="mw-geshi c source-c"><span class="br0">(</span><a href="c-chrono-clock_t.html"><span class="kw524">clock_t</span></a><span class="br0">)</span><span class="br0">(</span><span class="sy2">-</span><span class="nu0">1</span><span class="br0">)</span></span></span> 。</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>在兼容 POSIX 的系统上，带时钟 id <span class="t-c"><span class="mw-geshi c source-c">CLOCK_PROCESS_CPUTIME_ID</span></span> 的 <a rel="nofollow" class="external text" href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/clock_getres.html"><code>clock_gettime</code></a> 提供更高的解析度。</p>
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<p><code>clock()</code> 返回的值会在一些不遵从的实现上回卷。例如在某种实现上，若 <span class="t-lc"><a href="c-chrono-clock_t.html">clock_t</a></span> 为有符号 32 位整数而 <span class="t-lc"><a href="c-chrono-CLOCKS_PER_SEC.html">CLOCKS_PER_SEC</a></span> 为 1000000 ，则它将在约 2147 秒（约 36 分）后回卷。</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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<p>此示例演示 clock() 和现实时间之差异。</p>
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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 <time.h></span>
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<span class="co2">#include <stdlib.h></span>
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<span class="co2">#include <threads.h> // POSIX 中的 pthread.h</span>
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<span class="co1">// 函数 f() 做一些耗时的工作</span>
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<span class="kw4">int</span> f<span class="br0">(</span><span class="kw4">void</span><span class="sy2">*</span> thr_data<span class="br0">)</span> <span class="co1">// POSIX 中返回 void*</span>
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<span class="br0">{</span>
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<span class="kw4">volatile</span> <span class="kw4">double</span> d <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</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>
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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">10000</span><span class="sy4">;</span> <span class="sy2">++</span>m<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="kw1">return</span> <span class="nu0">0</span><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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<span class="kw1">struct</span> timespec ts1, tw1<span class="sy4">;</span> <span class="co1">// C11 与 POSIX 皆可</span>
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clock_gettime<span class="br0">(</span>CLOCK_PROCESS_CPUTIME_ID, <span class="sy3">&</span>ts1<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// POSIX</span>
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clock_gettime<span class="br0">(</span>CLOCK_MONOTONIC, <span class="sy3">&</span>tw1<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// POSIX ；C11 中用 timespec_get</span>
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<a href="c-chrono-clock_t.html"><span class="kw524">clock_t</span></a> t1 <span class="sy1">=</span> clock<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-thread.html"><span class="kw995">thrd_t</span></a> thr1, thr2<span class="sy4">;</span> <span class="co1">// C11 ；POSIX 中用 pthread_t</span>
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<a href="c-thread-thrd_create.html"><span class="kw996">thrd_create</span></a><span class="br0">(</span><span class="sy3">&</span>thr1, f, <a href="c-types-NULL.html"><span class="kw103">NULL</span></a><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// C11 ； POSIX 中用 pthread_create</span>
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<a href="c-thread-thrd_create.html"><span class="kw996">thrd_create</span></a><span class="br0">(</span><span class="sy3">&</span>thr2, f, <a href="c-types-NULL.html"><span class="kw103">NULL</span></a><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-thread-thrd_join.html"><span class="kw1003">thrd_join</span></a><span class="br0">(</span>thr1, <a href="c-types-NULL.html"><span class="kw103">NULL</span></a><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// C11 ； POSIX 中用 pthread_join</span>
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<a href="c-thread-thrd_join.html"><span class="kw1003">thrd_join</span></a><span class="br0">(</span>thr2, <a href="c-types-NULL.html"><span class="kw103">NULL</span></a><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">struct</span> timespec ts2, tw2<span class="sy4">;</span>
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clock_gettime<span class="br0">(</span>CLOCK_PROCESS_CPUTIME_ID, <span class="sy3">&</span>ts2<span class="br0">)</span><span class="sy4">;</span>
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clock_gettime<span class="br0">(</span>CLOCK_MONOTONIC, <span class="sy3">&</span>tw2<span class="br0">)</span><span class="sy4">;</span>
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<a href="c-chrono-clock_t.html"><span class="kw524">clock_t</span></a> t2 <span class="sy1">=</span> clock<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">double</span> dur <span class="sy1">=</span> <span class="nu16">1000.0</span><span class="sy2">*</span><span class="br0">(</span>t2<span class="sy2">-</span>t1<span class="br0">)</span><span class="sy2">/</span><a href="c-chrono-CLOCKS_PER_SEC.html"><span class="kw521">CLOCKS_PER_SEC</span></a><span class="sy4">;</span>
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<span class="kw4">double</span> posix_dur <span class="sy1">=</span> <span class="nu16">1000.0</span><span class="sy2">*</span>ts2.<span class="me1">tv_sec</span> <span class="sy2">+</span> <span class="nu19">1e-6</span><span class="sy2">*</span>ts2.<span class="me1">tv_nsec</span>
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<span class="sy2">-</span> <span class="br0">(</span><span class="nu16">1000.0</span><span class="sy2">*</span>ts1.<span class="me1">tv_sec</span> <span class="sy2">+</span> <span class="nu19">1e-6</span><span class="sy2">*</span>ts1.<span class="me1">tv_nsec</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">double</span> posix_wall <span class="sy1">=</span> <span class="nu16">1000.0</span><span class="sy2">*</span>tw2.<span class="me1">tv_sec</span> <span class="sy2">+</span> <span class="nu19">1e-6</span><span class="sy2">*</span>tw2.<span class="me1">tv_nsec</span>
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<span class="sy2">-</span> <span class="br0">(</span><span class="nu16">1000.0</span><span class="sy2">*</span>tw1.<span class="me1">tv_sec</span> <span class="sy2">+</span> <span class="nu19">1e-6</span><span class="sy2">*</span>tw1.<span class="me1">tv_nsec</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">"CPU time used (per clock(): %.2f ms<span class="es1">\n</span>"</span>, dur<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">"CPU time used (per clock_gettime()): %.2f ms<span class="es1">\n</span>"</span>, posix_dur<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">"Wall time passed: %.2f ms<span class="es1">\n</span>"</span>, posix_wall<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">CPU time used (per clock(): 1580.00 ms
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CPU time used (per clock_gettime()): 1582.76 ms
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Wall time passed: 792.13 ms</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>7.27.2.1 The clock function (p: 389)</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>7.23.2.1 The clock function (p: 339)</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>4.12.2.1 The clock function</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-chrono-ctime.html"><span class="t-lines"><span>ctime</span><span>ctime_r</span><span>ctime_s</span></span></a></div>
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<div><span class="t-lines"><span></span><span><span class="t-mark-rev t-since-c23">(C23)</span></span><span><span class="t-mark-rev t-since-c11">(C11)</span></span></span></div>
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</div>
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</td>
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<td>将 <code>struct time_t</code> 对象转换成文本表示<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="c-chrono-time.html"><span class="t-lines"><span>time</span></span></a></div>
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</div>
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</td>
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<td>返回纪元开始经过的当前系统日历时间<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>
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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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