nearbyint, nearbyintf, nearbyintl

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< c‎ | numeric‎ | math
 
 
 
常用数学函数
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基本运算
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指数函数
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幂函数
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三角及双曲函数
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误差及伽马函数
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临近整数的浮点运算
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nearbyint
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浮点数操作函数
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分类
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类型
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宏常量
 
定义于头文件 <math.h>
float       nearbyintf( float arg );
(1) (C99 起)
double      nearbyint( double arg );
(2) (C99 起)
long double nearbyintl( long double arg );
(3) (C99 起)
定义于头文件 <tgmath.h>
#define nearbyint( arg )
(4) (C99 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) 泛型宏:若 arg 拥有 long double 类型,则调用 nearbyintl 。否则,若 arg 拥有整数类型或 double 类型,则调用 nearbyint 。否则调用 nearbyintf

目录

[编辑] 参数值

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

nearbyintrint 之间仅有的区别是 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 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 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 <stdio.h>
#include <math.h>
#include <fenv.h>
 
int main(void)
{
#pragma STDC FENV_ACCESS ON
    fesetround(FE_TONEAREST);
    printf("rounding to nearest:\nnearbyint(+2.3) = %+.1f  ", nearbyint(2.3));
    printf("nearbyint(+2.5) = %+.1f  ", nearbyint(2.5));
    printf("nearbyint(+3.5) = %+.1f\n", nearbyint(3.5));
    printf("nearbyint(-2.3) = %+.1f  ", nearbyint(-2.3));
    printf("nearbyint(-2.5) = %+.1f  ", nearbyint(-2.5));
    printf("nearbyint(-3.5) = %+.1f\n", nearbyint(-3.5));
 
    fesetround(FE_DOWNWARD);
    printf("rounding down: \nnearbyint(+2.3) = %+.1f  ", nearbyint(2.3));
    printf("nearbyint(+2.5) = %+.1f  ", nearbyint(2.5));
    printf("nearbyint(+3.5) = %+.1f\n", nearbyint(3.5));
    printf("nearbyint(-2.3) = %+.1f  ", nearbyint(-2.3));
    printf("nearbyint(-2.5) = %+.1f  ", nearbyint(-2.5));
    printf("nearbyint(-3.5) = %+.1f\n", nearbyint(-3.5));
 
    printf("nearbyint(-0.0) = %+.1f\n", nearbyint(-0.0));
    printf("nearbyint(-Inf) = %+.1f\n", nearbyint(-INFINITY));
}

输出:

rounding to nearest:
nearbyint(+2.3) = +2.0  nearbyint(+2.5) = +2.0  nearbyint(+3.5) = +4.0
nearbyint(-2.3) = -2.0  nearbyint(-2.5) = -2.0  nearbyint(-3.5) = -4.0
rounding down: 
nearbyint(+2.3) = +2.0  nearbyint(+2.5) = +2.0  nearbyint(+3.5) = +3.0
nearbyint(-2.3) = -3.0  nearbyint(-2.5) = -3.0  nearbyint(-3.5) = -4.0
nearbyint(-0.0) = -0.0
nearbyint(-Inf) = -inf

[编辑] 引用

  • C11 standard (ISO/IEC 9899:2011):
  • 7.12.9.3 The nearbyint functions (p: 251-252)
  • 7.25 Type-generic math <tgmath.h> (p: 373-375)
  • F.10.6.3 The nearbyint functions (p: 526)
  • C99 standard (ISO/IEC 9899:1999):
  • 7.12.9.3 The nearbyint functions (p: 232)
  • 7.22 Type-generic math <tgmath.h> (p: 335-337)
  • F.9.6.3 The nearbyint functions (p: 463)

[编辑] 参阅

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使用当前舍入模式取整到整数,若结果有误则产生异常
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取整到最接近的整数,在相邻整数正中间时取远离零的数
(函数) [编辑]
获得或设置舍入方向
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nearbyintC++ 文档