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roundeven, roundevenf, roundevenl

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定义于头文件 <math.h>
float roundevenf ( float arg ) ;
(1) (C23 起)
double roundeven ( double arg ) ;
(2) (C23 起)
long double roundevenl ( long double arg ) ;
(3) (C23 起)
定义于头文件 <tgmath.h>
#define roundeven( arg )
(4) (C23 起)
1-3) 计算最接近 arg （以浮点格式表示）的整数值，将中间情况向最近的偶数取整，与当前舍入模式无关。
4) 类型泛型宏：若 arg 具有 long double 类型，则调用 roundevenl 。否则，若 arg 具有整数类型或 double 类型，则调用 roundeven 。否则，分别调用 roundevenf 。

目录

参数

arg - 浮点数值

返回值

如果未发生错误，则返回最接近 arg 的整数值，四舍五入到最接近的偶数整数。

错误处理

此函数不受 math_errhandling 中指定的任何错误影响。

如果实现支持 IEEE 浮点算术 (IEC 60559)：

  • FE_INEXACT 永不触发。
  • 若 arg 为 ±∞，则直接返回该值。
  • 若 arg 为 ±0，则直接返回该值。
  • 若 arg 为 NaN，则返回 NaN。

示例

运行此代码 
#include <math.h>
#include <stdio.h>
int main(void)
{
    printf("roundeven(+2.4) = %+.1f\n", roundeven(2.4));
    printf("roundeven(-2.4) = %+.1f\n", roundeven(-2.4));
    printf("roundeven(+2.5) = %+.1f\n", roundeven(2.5));
    printf("roundeven(-2.5) = %+.1f\n", roundeven(-2.5));
    printf("roundeven(+2.6) = %+.1f\n", roundeven(2.6));
    printf("roundeven(-2.6) = %+.1f\n", roundeven(-2.6));
    printf("roundeven(+3.5) = %+.1f\n", roundeven(3.5));
    printf("roundeven(-3.5) = %+.1f\n", roundeven(-3.5));
    printf("roundeven(-0.0) = %+.1f\n", roundeven(-0.0));
    printf("roundeven(-Inf) = %+f\n",   roundeven(-INFINITY));
}

可能的输出： 

roundeven(+2.4) = +2.0
roundeven(-2.4) = -2.0
roundeven(+2.5) = +2.0
roundeven(-2.5) = -2.0
roundeven(+2.6) = +3.0
roundeven(-2.6) = -3.0
roundeven(+3.5) = +4.0
roundeven(-3.5) = -4.0
roundeven(-0.0) = -0.0
roundeven(-Inf) = -inf

参考文献

  • C23 标准 (ISO/IEC 9899:2024):
  • 7.12.9.8 roundeven 函数集 (p: 265-266)
  • 7.27 泛型数学 <tgmath.h> (p: 386-390)
  • F.10.6.8 roundeven 函数集 (p: 532)

参见

(C99) (C99) (C99) (C99) (C99) (C99) (C99) (C99) (C99)
使用当前舍入模式将数值舍入为整数，
若结果不同则产生异常
(函数)
(C99) (C99) (C99) (C99) (C99) (C99) (C99) (C99) (C99)
舍入到最接近的整数，中间情况向远离零的方向舍入
(函数)