200 lines
12 KiB
HTML
200 lines
12 KiB
HTML
<!DOCTYPE html>
|
|
<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
|
|
<head><meta http-equiv="x-ua-compatible" content="ie=edge">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
<title>atof</title>
|
|
<link rel="stylesheet" href="ext.css" />
|
|
<link rel="stylesheet" href="site_modules.css" />
|
|
</head>
|
|
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_string_byte_atof skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading">atof</h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="c.html">c</a>‎ | <a href="c-string.html">string</a>‎ | <a href="c-string-byte.html">byte</a></span></div>
|
|
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dsc-header">
|
|
<td>
|
|
<div>定义于头文件 <code><stdlib.h></code></div>
|
|
</td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl">
|
|
<td class="t-dcl-nopad">
|
|
<div><span class="mw-geshi c source-c"><span class="kw4">double</span> atof<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> str <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td class="t-dcl-nopad"></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>转译 <code>str</code> 所指向的字节字符串中的浮点值。</p>
|
|
<p>函数会舍弃任何空白符（由 <span class="t-c"><span class="mw-geshi c source-c">std<span class="sy4">::</span><a href="c-string-byte-isspace.html"><span class="kw534">isspace</span></a><span class="br0">(</span><span class="br0">)</span></span></span> 确定），直至找到首个非空白符。然后它会取用尽可能多的字符，以构成合法的浮点数表示，并将它们转换成浮点值。合法的浮点值可以为下列之一：</p>
|
|
<ul>
|
|
<li>十进制浮点数表达式。它由下列部分组成：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li><span class="t-mark">(可选)</span> 正或负号</li>
|
|
<li>非空的十进制数字序列，可选地包含一个小数点字符（由当前的 C <a href="c-locale-setlocale.html">本地环境</a>确定）（定义有效数字）</li>
|
|
<li><span class="t-mark">(可选)</span> <code><b>e</b></code> 或 <code><b>E</b></code> ，并跟随可选的正或负号，以及非空十进制数字序列（以 10 为底定义指数）</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<table class="t-rev-begin">
|
|
<tr class="t-rev t-since-c99">
|
|
<td>
|
|
<ul>
|
|
<li>十六进制浮点数表达式。它由下列部分组成：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li><span class="t-mark">(可选)</span> 正或负号</li>
|
|
<li><code><b>0x</b></code> 或 <code><b>0X</b></code></li>
|
|
<li>非空的十六进制数字序列，选地包含一个小数点字符（由当前的 C <a href="c-locale-setlocale.html">本地环境</a>确定）（定义有效数字）</li>
|
|
<li><span class="t-mark">(可选)</span> <code><b>p</b></code> 或 <code><b>P</b></code> ，并跟随可选的正或负号，以及非空十进制数字序列（以 2 为底定义指数）</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<ul>
|
|
<li>无穷大表达式。它由下列部分组成：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li><span class="t-mark">(可选)</span> 正或负号</li>
|
|
<li><code><b>INF</b></code> 或 <code><b>INFINITY</b></code> ，忽略大小写</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<ul>
|
|
<li>非数（NaN）表达式。它由下列部分组成：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li><span class="t-mark">(可选)</span> 正或负号</li>
|
|
<li><code><b>NAN</b></code> 或 <code><b>NAN(</b></code><i>char_sequence</i><code><b>)</b></code> ，忽略 <code><b>NAN</b></code> 部分的大小写。 <i>char_sequence</i> 只能由数字、拉丁字母和下划线构成。结果是一个静态的 NaN 浮点值。</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
</td>
|
|
<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td>
|
|
</tr>
|
|
</table>
|
|
<ul>
|
|
<li>任何其他可由当前 C <a href="c-locale-setlocale.html">本地环境</a>接受的表达式</li>
|
|
</ul>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td>str</td>
|
|
<td>-</td>
|
|
<td>指向待转译的空终止字符串的指针</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
|
|
<p>成功时返回代表 <code>str</code> 内容的 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">double</span></span></span> 值。若转换的值在返回值范围外，则返回值未定义。若无可进行的转换，则返回 <span class="t-c"><span class="mw-geshi c source-c"><span class="nu16">0.0</span></span></span> 。</p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="c source-c">
|
|
<pre class="de1"><span class="co2">#include <stdlib.h></span>
|
|
<span class="co2">#include <stdio.h></span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%g<span class="es1">\n</span>"</span>, atof<span class="br0">(</span><span class="st0">" -0.0000000123junk"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%g<span class="es1">\n</span>"</span>, atof<span class="br0">(</span><span class="st0">"0.012"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%g<span class="es1">\n</span>"</span>, atof<span class="br0">(</span><span class="st0">"15e16"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%g<span class="es1">\n</span>"</span>, atof<span class="br0">(</span><span class="st0">"-0x1afp-2"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%g<span class="es1">\n</span>"</span>, atof<span class="br0">(</span><span class="st0">"inF"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%g<span class="es1">\n</span>"</span>, atof<span class="br0">(</span><span class="st0">"Nan"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%g<span class="es1">\n</span>"</span>, atof<span class="br0">(</span><span class="st0">"1.0e+309"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// UB ：超出 double 范围</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%g<span class="es1">\n</span>"</span>, atof<span class="br0">(</span><span class="st0">"0.0"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"%g<span class="es1">\n</span>"</span>, atof<span class="br0">(</span><span class="st0">"junk"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 无可进行的转换</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>可能的输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">-1.23e-08
|
|
0.012
|
|
1.5e+17
|
|
-107.75
|
|
inf
|
|
nan
|
|
inf
|
|
0
|
|
0</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
|
|
<div class="t-ref-std-11">
|
|
<ul>
|
|
<li>C11 标准（ISO/IEC 9899:2011）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>7.22.1.1 The atof function (p: 341)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<div class="t-ref-std-c99">
|
|
<ul>
|
|
<li>C99 标准（ISO/IEC 9899:1999）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>7.20.1.1 The atof function (p: 307)</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<div class="t-ref-std-c89">
|
|
<ul>
|
|
<li>C89/C90 标准（ISO/IEC 9899:1990）：</li>
|
|
</ul>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>4.10.1.1 The atof function</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="c-string-byte-strtof.html"><span class="t-lines"><span>strtof</span><span>strtod</span><span>strtold</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>将字节字符串转换成浮点值<br />
|
|
<span class="t-mark">(函数)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|