FP_NORMAL, FP_SUBNORMAL, FP_ZERO, FP_INFINITE, FP_NAN

描述

FP_NORMAL、FP_SUBNORMAL、FP_ZERO、FP_INFINITE、FP_NAN 宏分别表示浮点数的不同类别。它们都扩展为一个整数常量表达式。

常量	解释
FP_NORMAL	表示该值为正常值，即不是无穷大、次正规数、非数字或零
FP_SUBNORMAL	表示该值为次正规数
FP_ZERO	表示该值为正零或负零
FP_INFINITE	表示该值无法由底层类型表示（正无穷大或负无穷大）
FP_NAN	表示该值为非数字 (NaN)

声明

#define FP_NORMAL    /* implementation defined */

#define FP_SUBNORMAL /* implementation defined */

#define FP_ZERO      /* implementation defined */

#define FP_INFINITE  /* implementation defined */

#define FP_NAN       /* implementation defined */

示例

#include <cfloat>
#include <cmath>
#include <iostream>
 
auto show_classification(double x)
{
    switch (std::fpclassify(x))
    {
        case FP_INFINITE:
            return "Inf";
        case FP_NAN:
            return "NaN";
        case FP_NORMAL:
            return "normal";
        case FP_SUBNORMAL:
            return "subnormal";
        case FP_ZERO:
            return "zero";
        default:
            return "unknown";
    }
}
 
int main()
{
    std::cout 
        << "1.0/0.0 is " 
        << show_classification(1 / 0.0) << '\n'
        << "0.0/0.0 is " 
        << show_classification(0.0 / 0.0) << '\n'
        << "DBL_MIN/2 is " 
        << show_classification(DBL_MIN / 2) << '\n'
        << "-0.0 is " 
        << show_classification(-0.0) << '\n'
        << "1.0 is " 
        << show_classification(1.0) << '\n';
}

结果

1.0/0.0 is Inf
0.0/0.0 is NaN
DBL_MIN/2 is subnormal
-0.0 is zero
1.0 is normal