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文字

在头文件<math.h>中定义



float       ceilf( float arg );

(1)

(since C99)

double      ceil( double arg );

(2)


long double ceill( long double arg );

(3)

(since C99)

Defined in header <tgmath.h>



#define ceil( arg )

(4)

(since C99)

1-3)计算不小于的最小整数值arg

4)类型 - 通用宏:如果arg有类型long doubleceill被调用。否则,如果arg有整数类型或类型doubleceil则调用。否则,ceilf被调用。

参数

arg

-

浮点值

返回值

如果没有发生错误arg,则返回不小于的最小整数值,即⌈arg⌉。

返回值

论据

错误处理

按照math_errhandling中的指定报告错误。

如果实现支持IEEE浮点运算(IEC 60559),

  • 当前的舍入模式不起作用。

  • 如果arg是±∞,则返回,未修改

  • 如果arg为±0,则返回,未修改

  • 如果arg是NaN,则返回NaN

笔记

FE_INEXACT 在舍入非整数有限值时可能(但不是必须))。

最大的可表示浮点值是所有标准浮点格式中的精确整数,因此该函数不会自行溢出; 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)。

这个函数(用于双参数)的行为就像(FE_INEXACT由不执行的自由除外)一样。

#include <math.h>#include <fenv.h>#pragma STDC FENV_ACCESS ON
double ceil(double x){
    double result;
    int save_round = fegetround();    fesetround(FE_UPWARD);
    result = rint(x); // or nearbyint     fesetround(save_round);    return result;}

#include <math.h>#include <stdio.h>int main(void){    printf("ceil(+2.4) = %+.1f\n", ceil(2.4));    printf("ceil(-2.4) = %+.1f\n", ceil(-2.4));    printf("ceil(-0.0) = %+.1f\n", ceil(-0.0));    printf("ceil(-Inf) = %+f\n",   ceil(-INFINITY));}

可能的输出:

ceil(+2.4) = +3.0ceil(-2.4) = -2.0ceil(-0.0) = -0.0ceil(-Inf) = -inf

参考

  • C11标准(ISO / IEC 9899:2011):

    • 7.12.9.1细胞功能(p:251)

    • 7.25类型通用数学<tgmath.h>(p:373-375)

    • F.10.6.1 ceil函数(p:526)

  • C99标准(ISO / IEC 9899:1999):

    • 7.12.9.1细胞功能(p:231-232)

    • 7.22类型通用数学<tgmath.h>(p:335-337)

    • F.9.6.1 ceil函数(p:462-463)

  • C89 / C90标准(ISO / IEC 9899:1990):

    • 4.5.6.1 ceil函数

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