c++ - WEXITSTATUS 总是返回 0

Question

我正在分叉一个进程并wc使用execl. 现在在正确的参数下，它运行良好，但是当我给出错误的文件名时，它会失败，但在这两种情况下，返回值 WEXITSTATUS(status) 始终为 0。

我相信我正在做的事情有问题，但我不确定是什么。阅读手册页和谷歌建议我应该根据状态代码获得正确的值。

这是我的代码：

#include <iostream>
#include <unistd.h>

int main(int argc, const char * argv[])
{
    pid_t pid = fork();
    if(pid <0){
        printf("error condition");
    } else if(pid == 0) {
        printf("child process");
        execl("/usr/bin/wc", "wc", "-l", "/Users/gabbi/learning/test/xyz.st",NULL);
        printf("this happened");
    } else {
        int status;
        wait(&status);

        if( WIFEXITED( status ) ) {
            std::cout << "Child terminated normally" << std::endl;
            printf("exit status is %d",WEXITSTATUS(status));
            return 0;
        } else {     
        }
    }
}

score 1 · Accepted Answer

如果您提供一个不存在的文件的名称execl()作为第一个参数，它会失败。如果发生这种情况，程序会在不返回任何特定值的情况下离开。所以0返回默认值。

您可以像这样修复示例：

#include <errno.h>

...

int main(int argc, const char * argv[])
{
  pid_t pid = fork();
  if(pid <0){
    printf("error condition");
  } else if(pid == 0) {
    printf("child process");
    execl(...); /* In case exec succeeds it never returns. */
    perror("execl() failed");
    return errno; /* In case exec fails return something different then 0. */
  }
  ...

score 0 · Accepted Answer

您没有将文件名从 argv 传递给子进程

代替

 execl("/usr/bin/wc", "wc", "-l", "/Users/gabbi/learning/test/xyz.st",NULL);

尝试这个，

 execl("/usr/bin/wc", "wc", "-l", argv[1],NULL);

我在我的机器上得到的输出

xxx@MyUbuntu:~/cpp$ ./a.out test.txt 
6 test.txt
Child terminated normally
exit status is 0

xxx@MyUbuntu:~/cpp$ ./a.out /test.txt 
wc: /test.txt: No such file or directory
Child terminated normally
exit status is 1

score -1 · Accepted Answer

This was an xcode issue, running from console works fine. I am a Java guy, doing some assignments in CPP. Nevertheless, it might come handy to someone getting stuck at similar issue.

c++ - WEXITSTATUS 总是返回 0

3 回答 3

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