nearbyint, nearbyintf, nearbyintl

来自cppreference.com
< c‎ | numeric‎ | math
 
 
 
常用数学函数
函数
基本运算
(C99)
(C99)
(C99)
(C99)
(C99)
(C99)(C99)(C99)
指数函数
(C99)
(C99)
(C99)
(C99)
幂函数
(C99)
(C99)
三角及双曲函数
(C99)
(C99)
(C99)
误差及伽马函数
(C99)
(C99)
(C99)
(C99)
临近整数的浮点运算
(C99)(C99)(C99)
(C99)
nearbyint
(C99)
(C99)(C99)(C99)
浮点数操作函数
(C99)(C99)
(C99)
(C99)
分类
(C99)
(C99)
(C99)
类型
(C99)(C99)
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

参数值

arg - 浮点值

返回值

返回 arg 按照当前舍入模式的最接近整数值。

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

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 )。

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

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)

参阅

(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)
使用当前舍入模式取整到整数,若结果有误则产生异常
(函数)
(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)(C99)
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)
获得或设置数字的舍入方向
(函数)