c++ - 为什么系统函数在 C++ 中总是返回一个移位的退出状态？

Question

这个问题在这里已经有了答案:





Exit Codes from system() not as expected

(3 个回答)


1年前关闭。




我想启动一个脚本并在 C++ 中获取退出状态。但我注意到系统命令的退出状态总是左移 8 位。为什么系统功能会这样做？
示例代码:

#include <iostream>

using namespace std;

int main()
{
    int exit_code_0 = system("exit 0") >> 8;
    int exit_code_1 = system("exit 1") >> 8;
    int exit_code_2 = system("exit 2") >> 8;
    int exit_code_3 = system("exit 3") >> 8;
    int exit_code_4 = system("exit 4") >> 8;
    int exit_code_255 = system("exit 255")>> 8;
    cout<<"Exit code was: " << exit_code_0 <<", Expected: 0"<< endl;
    cout<<"Exit code was: " << exit_code_1 <<", Expected: 1"<< endl;
    cout<<"Exit code was: " << exit_code_2 <<", Expected: 2"<< endl;
    cout<<"Exit code was: " << exit_code_3 <<", Expected: 3"<< endl;
    cout<<"Exit code was: " << exit_code_4 <<", Expected: 4"<< endl;
    cout<<"Exit code was: " << exit_code_255 <<", Expected: 255"<< endl;
    
    return 0;
}

测试结果:

Exit code was: 0, Expected: 0                                                                                                                                                       
Exit code was: 1, Expected: 1                                                                                                                                                       
Exit code was: 2, Expected: 2                                                                                                                                                       
Exit code was: 3, Expected: 3                                                                                                                                                       
Exit code was: 4, Expected: 4                                                                                                                                                       
Exit code was: 255, Expected: 255

Answer 1

在 C 和 C++ 标准中，system返回实现定义的值。
在 POSIX 系统中，返回值包含不同值的组合，可以用宏提取。要获取程序的退出状态，请使用 WEXITSTATUS(return_value) ，在您的系统上定义为右移 8。低 8 位包含其他值(例如，让您确定程序是否正常退出或由于信号等)