nearbyint
nearbyint, nearbyintf, nearbyintl
| 在头文件 | | |
|---|---|---|
| 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）：
