Question

Here is a small piece of code, the parent process write pipe and child read pipe, everything works fine before I add ‘wait()’ in parent process. I think it should be no difference, but it just stucks when I input. I’m quite new to system programming. Anyone can help with this?

int main() {
      char* msg = malloc(sizeof(100));
      int fd[2];
      pipe(fd);
      int status;


if (fork()!=0){
    close(fd[0]);
    dup2(fd[1],1);
    scanf("%s",msg);
    puts(msg);
    wait(&status);
}
else {
    char* buf = malloc(sizeof(100));
    close(fd[1]);
    dup2(fd[0],0);
    scanf("%s",buf);
    puts(buf);
}
return 0;}

Answer 1

You have to flush stdout before calling wait().

Your program was working before without the wait() since an implicit flush was done when the parent process exit.