211 lines
17 KiB
HTML
211 lines
17 KiB
HTML
<!DOCTYPE html>
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<title>std::strtol, std::strtoll</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>strtol, <span style="font-size:0.7em; line-height:130%">std::</span>strtoll</h1>
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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>定义于头文件 <code><a href="cpp-header-cstdlib.html"><cstdlib></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> strtol<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span>str, <span class="kw4">char</span> <span class="sy2">**</span>str_end, <span class="kw4">int</span> base <span class="br0">)</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">long</span> strtoll<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span>str, <span class="kw4">char</span> <span class="sy2">**</span>str_end, <span class="kw4">int</span> base <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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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>舍弃所有空白符（以调用 <code>isspace()</code> 鉴别），直到找到首个非空白符，然后取尽可能多的字符组成<i>底 n</i> （其中 n=base ）的整数表示，并将它们转换成一个整数值。合法的整数值由下列部分组成：</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><span class="t-mark">(可选)</span>指示八进制底的前缀（ <code><b>0</b></code> ）（仅当底为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">8</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 时应用）</li>
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<li><span class="t-mark">(可选)</span>指示十六进制底的前缀（ <code><b>0x</b></code> 或 <code><b>0X</b></code> ）（仅当底为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">16</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> 时应用）</li>
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<li>一个数字序列</li>
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</ul>
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<p>底的合法集是 {0,2,3,...,36} 。合法数字集对于底 2 整数是 <code>{0,1</code>}，对于底3整数是 <code>{0,1,2</code>} ，以此类推。对于大于 <code>10</code> 的底，合法数字包含字母字符，从对于底 11 整数的 <code>Aa</code> 到对于底36整数的 <code>Zz</code> 。忽略字符大小写。</p>
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<p>当前安装的 C <a href="cpp-locale-setlocale.html">本地环境</a>可能接受另外的数字格式。</p>
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<p>若 base 为 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> ，则自动检测数值进制：若前缀为 <code><b>0</b></code> ，则底为八进制，若前缀为 <code><b>0x</b></code> 或 <code><b>0X</b></code> ，则底为十六进制，否则底为十进制。</p>
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<p>若符号是输入序列的一部分，则对从数字序列计算得来的数字值取反，如同用结果类型的<a href="cpp-language-operator_arithmetic.html#.E4.B8.80.E5.85.83.E7.AE.97.E6.9C.AF.E8.BF.90.E7.AE.97.E7.AC.A6">一元减</a>。</p>
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<p>函数设置 <code>str_end</code> 所指向的指针指向最后被转译字符的后一字符。若 <code>str_end</code> 为空指针，则忽略它。</p>
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<p>若 <code>str</code> 为空或无期待的形式，则不进行转换，并（若 <code>str_end</code> 非空指针）将 <code>str</code> 的值存储于 <code>str_end</code> 所指向的对象。</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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<td>str</td>
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<td>-</td>
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<td>指向要转译的空终止字符串的指针</td>
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<tr class="t-par">
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<td>str_end</td>
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<td>-</td>
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<td>指向指向字符指针的指针。</td>
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<tr class="t-par">
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<td>base</td>
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<td>-</td>
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<td>被转译整数值的<i>底</i></td>
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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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<ul>
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<li>若成功，则返回对应 <code>str</code> 内容的整数值。</li>
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<li>若转换出的值落在对应类型的范围外，则发生值域错误（设置 <span class="t-lc"><a href="cpp-error-errno.html">errno</a></span> 为 <span class="t-lc"><a href="cpp-error-errno_macros.html">ERANGE</a></span> ）并返回 <span class="t-lc"><a href="cpp-types-climits.html">LONG_MAX</a></span> 、 <span class="t-lc"><a href="cpp-types-climits.html">LONG_MIN</a></span> 、 <span class="t-lc"><a href="cpp-types-climits.html">LLONG_MAX</a></span> 或 <span class="t-lc"><a href="cpp-types-climits.html">LLONG_MIN</a></span> 。</li>
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<li>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> 。</li>
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</ul>
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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 <cerrno></span>
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<span class="co2">#include <cstdlib></span>
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<span class="co2">#include <iomanip></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <string></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> p <span class="sy1">=</span> <span class="st0">"10 200000000000000000000000000000 30 -40"</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Parsing "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-quoted.html"><span class="kw1800">std::<span class="me2">quoted</span></span></a><span class="br0">(</span>p<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">":<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="sy4">;;</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="co1">// 库函数调用能设置 errno 为任何非零值，无关乎是否有错误，</span>
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<span class="co1">// 故为检查 strtol 设置的错误，需要清除它</span>
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<span class="kw2">errno</span> <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
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<span class="kw4">char</span><span class="sy2">*</span> p_end<span class="sy4">;</span>
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<span class="kw4">const</span> <span class="kw4">long</span> i <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">strtol</span><span class="br0">(</span>p, <span class="sy3">&</span>p_end, <span class="nu0">10</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>p <span class="sy1">==</span> p_end<span class="br0">)</span>
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<span class="kw1">break</span><span class="sy4">;</span>
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<span class="kw4">const</span> <span class="kw4">bool</span> range_error <span class="sy1">=</span> <span class="kw2">errno</span> <span class="sy1">==</span> <a href="cpp-error-errno_macros.html"><span class="kw862">ERANGE</span></a><span class="sy4">;</span>
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<span class="kw4">const</span> <a href="cpp-string-basic_string.html"><span class="kw1228">std::<span class="me2">string</span></span></a> extracted<span class="br0">(</span>p, p_end <span class="sy2">-</span> p<span class="br0">)</span><span class="sy4">;</span>
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p <span class="sy1">=</span> p_end<span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Extracted "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-quoted.html"><span class="kw1800">std::<span class="me2">quoted</span></span></a><span class="br0">(</span>extracted<span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">", strtol returned "</span> <span class="sy1"><<</span> i <span class="sy1"><<</span> <span class="st0">'.'</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>range_error<span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">" Range error occurred."</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a> <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>
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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">Parsing "10 200000000000000000000000000000 30 -40":
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Extracted "10", strtol returned 10.
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Extracted " 200000000000000000000000000000", strtol returned 9223372036854775807. Range error occurred.
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Extracted " 30", strtol returned 30.
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Extracted " -40", strtol returned -40.</pre></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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<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-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-string-wide-wcstol.html"><span class="t-lines"><span>wcstol</span><span>wcstoll</span></span></a></div>
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</div>
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</td>
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<td>转换宽字符串为整数值<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-strtof.html"><span class="t-lines"><span>strtof</span><span>strtod</span><span>strtold</span></span></a></div>
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</div>
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</td>
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<td>转换字节字符串为浮点值<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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<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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<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-atoi.html"><span class="t-lines"><span>atoi</span><span>atol</span><span>atoll</span></span></a></div>
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<div><span class="t-lines"><span></span><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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</table>
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</div>
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<div class="visualClear"></div>
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</body>
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