# std::fetestexcept

< cpp‎ | numeric‎ | fenv

定义于头文件 `<cfenv>` |  |
int fetestexcept( int excepts ); |  | (C++11 起)

确定当前设定了哪个浮点异常的指定子集。参数 `excepts` 是浮点异常宏的逐位或。

### 参数

excepts | - | 列出要测试的异常标志的位掩码

### 返回值

包含于 `excepts` 而且对应于当前设置的浮点异常中的浮点异常宏的逐位或。

### 示例

    #include <iostream>
    #include <cfenv>
    #include <cmath>

    #pragma STDC FENV_ACCESS ON

    volatile double zero = 0.0; // 支持 FENV_ACCESS 处不需要 volatile
    volatile double one = 1.0;  // 支持 FENV_ACCESS 处不需要 volatile

    int main()
    {
        std::feclearexcept(FE_ALL_EXCEPT);
        std::cout <<  "1.0/0.0 = " << 1.0 / zero << '\n';
        if(std::fetestexcept(FE_DIVBYZERO)) {
            std::cout << "division by zero reported\n";
        } else {
            std::cout << "divsion by zero not reported\n";
        }

        std::feclearexcept(FE_ALL_EXCEPT);
        std::cout << "1.0/10 = " << one/10 << '\n';
        if(std::fetestexcept(FE_INEXACT)) {
            std::cout << "inexact result reported\n";
        } else {
            std::cout << "inexact result not reported\n";
        }

        std::feclearexcept(FE_ALL_EXCEPT);
        std::cout << "sqrt(-1) = " << std::sqrt(-1) << '\n';
        if(std::fetestexcept(FE_INVALID)) {
            std::cout << "invalid result reported\n";
        } else {
            std::cout << "invalid result not reported\n";
        }
    }

输出：

    1.0/0.0 = inf
    division by zero reported
    1.0/10 = 0.1
    inexact result reported
    sqrt(-1) = -nan
    invalid result reported

### 参阅

feclearexcept (C++11) | 清除指定的浮点状态标志 (函数)