std::nearbyint

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< cpp‎ | numeric‎ | math
 
 
 
常用数学函数
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基本运算
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误差与伽马函数
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临近整数的浮点运算
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nearbyint
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浮点操作函数
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宏常量
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定义于头文件 <cmath>
float       nearbyint( float arg );
(1) (C++11 起)
double      nearbyint( double arg );
(2) (C++11 起)
long double nearbyint( long double arg );
(3) (C++11 起)
double      nearbyint( Integral arg );
(4) (C++11 起)
1-3)当前舍入模式,舍入浮点参数 arg 到浮点格式的整数值。
4) 接受任何整数类型参数的重载集或函数模板。等价于 (2) (将参数转型为 double )。

目录

[编辑] 参数

arg - 浮点值

[编辑] 返回值

返回 arg 按照当前舍入模式的最接近整数值。

[编辑] 错误处理

此函数不受制于任何指定于 math_errhandling 的错误。

若实现支持 IEEE 浮点算术( IEC 60559 ),则

  • 决不引发 FE_INEXACT
  • arg 为 ±∞ ,则返回不修改的参数
  • arg 为 ±0 ,则返回不修改的参数
  • arg 为 NaN ,则返回 NaN

[编辑] 注意

std::nearbyintrint 之间仅有的区别是 std::nearbyint 决不引发 FE_INEXACT

所有标准浮点格式中,最大可表示浮点值都是整数,故 std::nearbyint 自身决不溢出;然而存储结果于整数对象时,结果可能溢出任何整数类型(包含 std::intmax_t )。

若当前舍入模式为 FE_TONEAREST ,则此函数在中点情况向偶数舍入(同 rint ,但不同于 round )。

[编辑] 示例

#include <iostream>
#include <cmath>
#include <cfenv>
 
int main()
{
#pragma STDC FENV_ACCESS ON
    std::fesetround(FE_TONEAREST);
    std::cout << "rounding to nearest: \n"
              << "nearbyint(+2.3) = " << std::nearbyint(2.3)
              << "  nearbyint(+2.5) = " << std::nearbyint(2.5)
              << "  nearbyint(+3.5) = " << std::nearbyint(3.5) << '\n'
              << "nearbyint(-2.3) = " << std::nearbyint(-2.3)
              << "  nearbyint(-2.5) = " << std::nearbyint(-2.5)
              << "  nearbyint(-3.5) = " << std::nearbyint(-3.5) << '\n';
 
    std::fesetround(FE_DOWNWARD);
    std::cout << "rounding down:\n"
              << "nearbyint(+2.3) = " << std::nearbyint(2.3)
              << "  nearbyint(+2.5) = " << std::nearbyint(2.5)
              << "  nearbyint(+3.5) = " << std::nearbyint(3.5) << '\n'
              << "nearbyint(-2.3) = " << std::nearbyint(-2.3)
              << "  nearbyint(-2.5) = " << std::nearbyint(-2.5)
              << "  nearbyint(-3.5) = " << std::nearbyint(-3.5) << '\n';
 
    std::cout << "nearbyint(-0.0) = " << std::nearbyint(-0.0)  << '\n'
              << "nearbyint(-Inf) = " << std::nearbyint(-INFINITY) << '\n';
}

输出:

rounding to nearest: 
nearbyint(+2.3) = 2  nearbyint(+2.5) = 2  nearbyint(+3.5) = 4
nearbyint(-2.3) = -2  nearbyint(-2.5) = -2  nearbyint(-3.5) = -4
rounding down:
nearbyint(+2.3) = 2  nearbyint(+2.5) = 2  nearbyint(+3.5) = 3
nearbyint(-2.3) = -3  nearbyint(-2.5) = -3  nearbyint(-3.5) = -4
nearbyint(-0.0) = -0
nearbyint(-Inf) = -inf

[编辑] 参阅

(C++11)
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使用当前舍入模式的最接近整数
若结果有别则有异常
(函数) [编辑]
(C++11)
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最接近整数,中间情况下舍入到远离零
(函数) [编辑]
(C++11)
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获取或设置舍入方向
(函数) [编辑]
nearbyintC 文档