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web/cppreference-zh/chmhelp/cpp-string-byte-atoi.html
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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>std::atoi, std::atol, std::atoll</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_string_byte_atoi 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>atoi, <span style="font-size:0.7em; line-height:130%">std::</span>atol, <span style="font-size:0.7em; line-height:130%">std::</span>atoll</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-string.html">string</a>‎ | <a href="cpp-string-byte.html">byte</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-cstdlib.html"><cstdlib></a></code></div>
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</td>
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<td></td>
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<td></td>
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<td class="t-dcl-nopad">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">int</span> atoi<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>
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<td class="t-dcl-nopad">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> atol<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>
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<td class="t-dcl-nopad"></td>
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<tr class="t-dcl t-since-cxx11">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">long</span> atoll<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>
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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-cxx11">(C++11 起)</span></td>
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</tr>
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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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</tr>
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</tbody>
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</table>
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<p>转译 <code>str</code> 所指向的字节字符串中的整数值。</p>
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<p>舍弃任何空白符，直至找到首个非空白符，然后接收尽可能多的字符以组成合法的整数表示，并转换之为整数值。合法的整数值含下列部分：</p>
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<ul>
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<li><span class="t-mark">(可选)</span> 正或负号</li>
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<li>数位</li>
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</ul>
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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>str</td>
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<td>-</td>
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<td>指向要转译的空终止字节字符串的指针</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>成功时为对应 <code>str</code> 内容的整数值。若转换出的值落在对应返回类型的范围外，则返回值未定义。若不能进行转换，则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 。</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 <cstdlib></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="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span>str1 <span class="sy1">=</span> <span class="st0">"42"</span><span class="sy4">;</span>
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<span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span>str2 <span class="sy1">=</span> <span class="st0">"3.14159"</span><span class="sy4">;</span>
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<span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span>str3 <span class="sy1">=</span> <span class="st0">"31337 with words"</span><span class="sy4">;</span>
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<span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span>str4 <span class="sy1">=</span> <span class="st0">"words and 2"</span><span class="sy4">;</span>
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<span class="kw4">int</span> num1 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">atoi</span><span class="br0">(</span>str1<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> num2 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">atoi</span><span class="br0">(</span>str2<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> num3 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">atoi</span><span class="br0">(</span>str3<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">int</span> num4 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">atoi</span><span class="br0">(</span>str4<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1755">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"std::atoi(<span class="es1">\"</span>"</span> <span class="sy1"><<</span> str1 <span class="sy1"><<</span> <span class="st0">"<span class="es1">\"</span>) is "</span> <span class="sy1"><<</span> num1 <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1755">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"std::atoi(<span class="es1">\"</span>"</span> <span class="sy1"><<</span> str2 <span class="sy1"><<</span> <span class="st0">"<span class="es1">\"</span>) is "</span> <span class="sy1"><<</span> num2 <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1755">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"std::atoi(<span class="es1">\"</span>"</span> <span class="sy1"><<</span> str3 <span class="sy1"><<</span> <span class="st0">"<span class="es1">\"</span>) is "</span> <span class="sy1"><<</span> num3 <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1755">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"std::atoi(<span class="es1">\"</span>"</span> <span class="sy1"><<</span> str4 <span class="sy1"><<</span> <span class="st0">"<span class="es1">\"</span>) is "</span> <span class="sy1"><<</span> num4 <span class="sy1"><<</span> <span class="st0">'<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">std::atoi("42") is 42
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std::atoi("3.14159") is 3
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std::atoi("31337 with words") is 31337
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std::atoi("words and 2") is 0</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">
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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="cpp-string-basic_string-stol.html"><span class="t-lines"><span>stoi</span><span>stol</span><span>stoll</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><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><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>转换字符串为有符号整数<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="cpp-string-basic_string-stoul.html"><span class="t-lines"><span>stoul</span><span>stoull</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><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>转换字符串为无符号整数<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="cpp-string-byte-strtol.html"><span class="t-lines"><span>strtol</span><span>strtoll</span></span></a></div>
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<div><span class="t-lines"><span></span><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>转换字节字符串为整数值<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="cpp-string-byte-strtoul.html"><span class="t-lines"><span>strtoul</span><span>strtoull</span></span></a></div>
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<div><span class="t-lines"><span></span><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>转换字节字符串为无符号整数值<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="cpp-string-byte-strtoimax.html"><span class="t-lines"><span>strtoimax</span><span>strtoumax</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><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>转换字节字符串为 <span class="t-lc"><a href="cpp-types-integer.html">std::intmax_t</a></span> 或 <span class="t-lc"><a href="cpp-types-integer.html">std::uintmax_t</a></span><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="cpp-utility-from_chars.html"><span class="t-lines"><span>from_chars</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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</div>
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</td>
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<td>转换字符序列到整数或浮点值<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 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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