221 lines
18 KiB
HTML
221 lines
18 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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<title>标准库头文件 <cfloat></title>
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<link rel="stylesheet" href="ext.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_header_cfloat skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">标准库头文件</span> <cfloat></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-header.html">header</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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<p>此头文件原作为 <code><b><float.h></b></code> 存在于 C 标准库。</p>
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<p>此头文件是<a href="cpp-types.html">类型支持</a>库的一部分，特别是它是 <a href="cpp-types-climits.html">C 数值极限接口</a>的一部分。</p>
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<h3><span class="mw-headline" id=".E5.AE.8F">宏</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><span class="t-lines"><span>FLT_RADIX</span></span></div>
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</div>
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</td>
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<td>所有三种浮点类型的表示所用的基数（整数底）<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>DECIMAL_DIG</span></span></div>
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<div><span class="t-lines"><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>从 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 转换到至少有 <code>DECIMAL_DIG</code> 位数字的十进制表示，再转换回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 为恒等转换：这是序列化/反序列化 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 所要求的十进制精度（参阅 <span class="t-lc"><a href="cpp-types-numeric_limits-max_digits10.html">std::numeric_limits::max_digits10</a></span>）<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>FLT_DECIMAL_DIG</span><span>DBL_DECIMAL_DIG</span><span>LDBL_DECIMAL_DIG</span></span></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>从 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>/<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span>/<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 转换到至少有 <code>FLT_DECIMAL_DIG</code>/<code>DBL_DECIMAL_DIG</code>/<code>LDBL_DECIMAL_DIG</code> 位数字的十进制，再转换回原类型为恒等转换：这是序列化/反序列化浮点值所要求的十进制精度（参阅 <span class="t-lc"><a href="cpp-types-numeric_limits-max_digits10.html">std::numeric_limits::max_digits10</a></span>）。分别定义为至少 6、10 和 10，对于 IEEE float 为 9，对于 IEEE double 为 17。<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>FLT_MIN</span><span>DBL_MIN</span><span>LDBL_MIN</span></span></div>
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</div>
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</td>
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<td>分别为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 的最小规格化正数值<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>FLT_TRUE_MIN</span><span>DBL_TRUE_MIN</span><span>LDBL_TRUE_MIN</span></span></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>分别为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 的最小正数值<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>FLT_MAX</span><span>DBL_MAX</span><span>LDBL_MAX</span></span></div>
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</div>
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</td>
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<td>分别为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 的最大有限值<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>FLT_EPSILON</span><span>DBL_EPSILON</span><span>LDBL_EPSILON</span></span></div>
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</div>
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</td>
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<td>分别为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu16">1.0</span></span></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 及 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 的下一个可表示值之差<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>FLT_DIG</span><span>DBL_DIG</span><span>LDBL_DIG</span></span></div>
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</div>
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</td>
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<td>保证能在文本→ <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>/<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span>/<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> →文本的往返转换中保留而不会因舍入或溢出发生改变的的十进制位数（解释参阅 <span class="t-lc"><a href="cpp-types-numeric_limits-digits10.html">std::numeric_limits::digits10</a></span>）<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>FLT_MANT_DIG</span><span>DBL_MANT_DIG</span><span>LDBL_MANT_DIG</span></span></div>
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</div>
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</td>
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<td>分别为能无精度损失地表示成 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 及 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 的基数 <code>FLT_RADIX</code> 的数字位数<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>FLT_MIN_EXP</span><span>DBL_MIN_EXP</span><span>LDBL_MIN_EXP</span></span></div>
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</div>
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</td>
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<td>分别为能够使<code>FLT_RADIX</code> 的该整数减一次幂为规格化的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 的最小负整数<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>FLT_MIN_10_EXP</span><span>DBL_MIN_10_EXP</span><span>LDBL_MIN_10_EXP</span></span></div>
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</div>
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</td>
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<td>分别为能够使 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">10</span></span></span> 的该整数减一次幂为规格化的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 的最小负整数<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>FLT_MAX_EXP</span><span>DBL_MAX_EXP</span><span>LDBL_MAX_EXP</span></span></div>
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</div>
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</td>
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<td>分别为能够使 <code>FLT_RADIX</code> 的该整数减一次幂为可表示的有限的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 的最大正整数<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>FLT_MAX_10_EXP</span><span>DBL_MAX_10_EXP</span><span>LDBL_MAX_10_EXP</span></span></div>
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</div>
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</td>
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<td>分别为能够使 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">10</span></span></span> 的该整数减一次幂为可表示的有限的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span>、<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 的最大正整数<br />
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<span class="t-mark">(宏常量)</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-types-climits-FLT_ROUNDS.html"><span class="t-lines"><span>FLT_ROUNDS</span></span></a></div>
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</div>
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</td>
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<td>浮点算术的默认舍入模式<br />
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<span class="t-mark">(宏常量)</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-types-climits-FLT_EVAL_METHOD.html"><span class="t-lines"><span>FLT_EVAL_METHOD</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></div>
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</div>
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</td>
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<td>指定进行所有算术运算所用的精度<br />
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<span class="t-mark">(宏常量)</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><span class="t-lines"><span>FLT_HAS_SUBNORM</span><span>DBL_HAS_SUBNORM</span><span>LDBL_HAS_SUBNORM</span></span></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>指明类型是否支持<a href="https://en.wikipedia.org/wiki/Denormal_number" class="extiw" title="enwiki:Denormal number">非正规</a>数值：-1 为不确定，0 为不支持，1 为支持。<br />
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<span class="t-mark">(宏常量)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E6.A6.82.E8.A6.81">概要</span></h3>
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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">#define FLT_ROUNDS /* 见定义 */</span>
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<span class="co2">#define FLT_EVAL_METHOD /* 见定义 */</span>
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<span class="co2">#define FLT_HAS_SUBNORM /* 见定义 */</span>
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<span class="co2">#define DBL_HAS_SUBNORM /* 见定义 */</span>
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<span class="co2">#define LDBL_HAS_SUBNORM /* 见定义 */</span>
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<span class="co2">#define FLT_RADIX /* 见定义 */</span>
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<span class="co2">#define FLT_MANT_DIG /* 见定义 */</span>
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<span class="co2">#define DBL_MANT_DIG /* 见定义 */</span>
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<span class="co2">#define LDBL_MANT_DIG /* 见定义 */</span>
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<span class="co2">#define FLT_DECIMAL_DIG /* 见定义 */</span>
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<span class="co2">#define DBL_DECIMAL_DIG /* 见定义 */</span>
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<span class="co2">#define LDBL_DECIMAL_DIG /* 见定义 */</span>
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<span class="co2">#define DECIMAL_DIG /* 见定义 */</span>
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<span class="co2">#define FLT_DIG /* 见定义 */</span>
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<span class="co2">#define DBL_DIG /* 见定义 */</span>
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<span class="co2">#define LDBL_DIG /* 见定义 */</span>
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<span class="co2">#define FLT_MIN_EXP /* 见定义 */</span>
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<span class="co2">#define DBL_MIN_EXP /* 见定义 */</span>
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<span class="co2">#define LDBL_MIN_EXP /* 见定义 */</span>
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<span class="co2">#define FLT_MIN_10_EXP /* 见定义 */</span>
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<span class="co2">#define DBL_MIN_10_EXP /* 见定义 */</span>
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<span class="co2">#define LDBL_MIN_10_EXP /* 见定义 */</span>
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<span class="co2">#define FLT_MAX_EXP /* 见定义 */</span>
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<span class="co2">#define DBL_MAX_EXP /* 见定义 */</span>
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<span class="co2">#define LDBL_MAX_EXP /* 见定义 */</span>
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<span class="co2">#define FLT_MAX_10_EXP /* 见定义 */</span>
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<span class="co2">#define DBL_MAX_10_EXP /* 见定义 */</span>
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<span class="co2">#define LDBL_MAX_10_EXP /* 见定义 */</span>
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<span class="co2">#define FLT_MAX /* 见定义 */</span>
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<span class="co2">#define DBL_MAX /* 见定义 */</span>
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<span class="co2">#define LDBL_MAX /* 见定义 */</span>
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<span class="co2">#define FLT_EPSILON /* 见定义 */</span>
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<span class="co2">#define DBL_EPSILON /* 见定义 */</span>
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<span class="co2">#define LDBL_EPSILON /* 见定义 */</span>
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<span class="co2">#define FLT_MIN /* 见定义 */</span>
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<span class="co2">#define DBL_MIN /* 见定义 */</span>
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<span class="co2">#define LDBL_MIN /* 见定义 */</span>
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<span class="co2">#define FLT_TRUE_MIN /* 见定义 */</span>
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<span class="co2">#define DBL_TRUE_MIN /* 见定义 */</span>
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<span class="co2">#define LDBL_TRUE_MIN /* 见定义 */</span></pre></div>
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