我应该在这段代码中使用waitpid和waitpid？

Question

我写了一个程序，它模拟'$ ls -l | wc -c'就像使用管道的命令一样。 现在我无法找到应该在这段代码中使用waitpid或waitpid的位置。

另外我应该关闭管道？ 请查看我的代码并提出建议。

int main ( int argc , char *argv[]) 
{ 

char *cmd_one_tokens[MAX]; /* Array of pointer to hold tokens of first command */ 
char *cmd_two_tokens[MAX]; /* Array of pointer to hold tokens of second command */ 

pid_t pid_one = -1 , /* variable to hold process id of first sub process */ 
     pid_two = -1 ; /* variable to hold process id of second sub process */ 
int status = -1 ; /* variable to read the status of the child process */ 
int pipe_fd[2] = {-1,-1}; /* Array to hold descriptors returned by pipe sys call */ 
int ret_val =-1 ; /* variable to hold return values by system calls */ 

/*Validate Number of command line arguments */ 
if(3 != argc) 
{ 
    printf("Provide Appropriate Arguments \n <lab3> < \"arg1\" > < \"arg2\" > \n"); 
    _exit(FAILURE); 

} 
/*Parse first command and get the tokens */ 
parse_command(argv[1],cmd_one_tokens); 
/*Parse second command and get the tokens */ 
parse_command(argv[2],cmd_two_tokens); 


/* Create pipe */ 
ret_val=pipe(pipe_fd); 
/*Error check */ 
if(ERROR==ret_val) 
{ 
    perror("Pipe creation error \n"); 
    _exit(FAILURE); 
} 
/*Fork First Child */ 
pid_one = fork() ; 
//Error check 
if(0 == pid_one) /*child process block */ 
{ 

    /* redirect stdout to pipe's write end for sub process one*/ 
    dup2(pipe_fd[1],1); 

    /*close pipe read end */ 
    close(pipe_fd[0]); 

    execvp(cmd_one_tokens[0],cmd_one_tokens); 

    /* if execvp returns then if must have failed */ 
    //Error check 

} 
else /*main process block */ 
{ 

    /*Wait for first sub process to finish */ 
    waitpid (pid_two , &status ,0); // <-------changes 

    /*Fork second subprocess */ 
    pid_two = fork(); 
      //Error check 
    if(0 == pid_two) /*second child process block */ 
    { 
     /* redirect stdin to pipe's read end for sub process two */ 
     dup2(pipe_fd[0],0); 

     /*close pipe write end */ 
     close(pipe_fd[1]); 

     execvp(cmd_two_tokens[0] , cmd_two_tokens); 
     /* if execvp returns then if must have failed */ 
     //Error check 

    } 
    else  /*main process block */ 
    { 
     status=-1; /*reset status */ 

     /*Waiting for the second sub process to finish in No hang fashion */ 
      waitpid (pid_two , &status ,0); // <-------changes 

    } 
} 
return(SUCCESS);   

}/*End of main */ 

Answer 1

您可以将父进程while循环（孩子们催生后）调用wait持续，直到两个孩子终止：

while (wait(&status) != -1); 

在您的特定情况下，你能避免waitpid。