126 lines
6.8 KiB
HTML
126 lines
6.8 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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<title>float_t, double_t</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_numeric_math_float_t 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">float_t, double_t</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-numeric.html">numeric</a>‎ | <a href="c-numeric-math.html">math</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><math.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 t-since-c99">
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<div><span class="mw-geshi c source-c"><span class="kw1">typedef</span> <span class="coMULTI">/*implementation defined*/</span> float_t</span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td>
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<tr class="t-dcl t-since-c99">
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<td>
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<div><span class="mw-geshi c source-c"><span class="kw1">typedef</span> <span class="coMULTI">/*implementation defined*/</span> double_t</span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-c99">(C99 起)</span></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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<td></td>
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</tbody>
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<p><span class="t-c"><span class="mw-geshi c source-c">float_t</span></span> 和 <span class="t-c"><span class="mw-geshi c source-c">double_t</span></span> 类型分别是至少与 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">float</span></span></span> 和 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">double</span></span></span> 一样宽的浮点类型，并满足 <span class="t-c"><span class="mw-geshi c source-c">double_t</span></span> 至少与 <span class="t-c"><span class="mw-geshi c source-c">float_t</span></span> 一样宽。 <span class="t-lc"><a href="c-types-limits-FLT_EVAL_METHOD.html">FLT_EVAL_METHOD</a></span> 的值确定 <span class="t-c"><span class="mw-geshi c source-c">float_t</span></span> 和 <span class="t-c"><span class="mw-geshi c source-c">double_t</span></span> 的类型。</p>
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<table class="t-dsc-begin">
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<tr class="t-dsc-hitem">
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<td>FLT_EVAL_METHOD</td>
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<td>解释</td>
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</tr>
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<tr class="t-dsc">
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<td><code>0</code></td>
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<td><span class="t-c"><span class="mw-geshi c source-c">float_t</span></span> 和 <span class="t-c"><span class="mw-geshi c source-c">double_t</span></span> 分别等价于 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">float</span></span></span> 和 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">double</span></span></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>1</code></td>
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<td><span class="t-c"><span class="mw-geshi c source-c">float_t</span></span> 和 <span class="t-c"><span class="mw-geshi c source-c">double_t</span></span> 都等价于 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">double</span></span></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>2</code></td>
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<td><span class="t-c"><span class="mw-geshi c source-c">float_t</span></span> 和 <span class="t-c"><span class="mw-geshi c source-c">double_t</span></span> 都等价于 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">double</span></span></span></td>
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</tr>
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<tr class="t-dsc">
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<td>其他</td>
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<td><span class="t-c"><span class="mw-geshi c source-c">float_t</span></span> 和 <span class="t-c"><span class="mw-geshi c source-c">double_t</span></span> 均为实现定义</td>
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</tr>
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</table>
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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 <float.h></span>
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<span class="co2">#include <math.h></span>
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<span class="co2">#include <stdio.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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<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>, <a href="c-types-limits-FLT_EVAL_METHOD.html"><span class="kw402">FLT_EVAL_METHOD</span></a><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%zu %zu<span class="es1">\n</span>"</span>, <span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">float</span><span class="br0">)</span>,<span class="kw4">sizeof</span><span class="br0">(</span>float_t<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"%zu %zu<span class="es1">\n</span>"</span>, <span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">double</span><span class="br0">)</span>,<span class="kw4">sizeof</span><span class="br0">(</span>double_t<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>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">0
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4 4
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8 8</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>7.12 Mathematics <math.h> (p: 231)</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>7.12 Mathematics <math.h> (p: 212)</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>
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</div>
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<div class="visualClear"></div>
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</div>
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