nearbyintl

nearbyint, nearbyintf, nearbyintl

在头文件中定义
float nearbyintf( float arg	(1)	(since C99)
double nearbyint( double arg	(2)	(since C99)
long double nearbyintl( long double arg	(3)	(since C99)
Defined in header <tgmath.h>
#define nearbyint( arg )	(4)	(since C99)

1-3）arg使用当前舍入模式将浮点参数四舍五入为浮点格式的整数值。

4）类型 - 通用宏：如果arg有类型long double，nearbyintl被调用。否则，如果arg有整数类型或类型double，nearbyint则调用。否则nearbyintf，分别称为。

参数

arg	-	浮点值

返回值

arg根据当前舍入模式，返回最接近的整数值。

错误处理

此函数不受math_errhandling中指定的任何错误的影响。

如果实现支持IEEE浮点运算（IEC 60559），

FE_INEXACT 从未被提出

笔记

之间唯一的区别nearbyint和rint是nearbyint永远不会提高FE_INEXACT。

最大的可表示浮点值是所有标准浮点格式中的精确整数，因此nearbyint不会自行溢出; 但是intmax_t，当存储在整数变量中时，结果可能会溢出任何整数类型（包括）。

如果当前的舍入模式是FE_TONEAREST，这个函数甚至在一半的情况下（例如rint，但不像round）。

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

参考

C11标准（ISO / IEC 9899：2011）：