c - 使用 fork 两次 - 奇怪的行为

Question

我正在尝试创建 2 个子进程并将它们与管道连接，但我的代码出了点问题。

int des_p[2];
if(pipe(des_p) == -1) {
    perror("Pipe failed");
    exit(1);
}
if((this->procId = fork())==0){ //filter for only the SON process to pass
    close(STDOUT_FILENO);   //closing stdout
    dup(des_p[1]);      //replacing stdout with pipe write 
    close(des_p[0]);    //closing pipe read
    close(des_p[1]);    //closing pipe write

    execvp(op1, argsp1);
    perror("execvp failed");
    exit(1);
}
if(this->procIdSecondary = fork() == 0)            //creating 2nd child, also a filter for only the SON process to pass
{
    close(STDIN_FILENO);    //closing stdin
    dup(des_p[0]);      //replacing stdin with pipe read
    close(des_p[1]);    //closing pipe write
    close(des_p[0]);    //closing pipe read

    execvp(op2, argsp2);
    perror("execvp failed");
    exit(1);
}
else
{
        cout <<"pid=" << this->procIdSecondary<<endl;

}

close(des_p[0]); 
close(des_p[1]);

`

我得到 pid=0

这怎么可能？

Answer 1

您的问题是此 if 语句中的运算符优先级

if(this->procIdSecondary = fork() == 0)

this->procIdSecondary 被分配比较的结果。在第一个 if 中添加括号。