WIFSTOPPED is not working properly

I am trying to implement the fg command in my mini shell. The problem is as follows:

• A process(gedit) is started in foreground.
• I stop with ctrl+z and check exit my wait loop by checking the return value of WIFSTOPPED(status):

while(1){
    pid_t pid_check = waitpid(pid,&signal,WNOHANG|WUNTRACED);
    if(pid_check == pid){
        if(WIFSTOPPED(signal)){
            tempid = pid_check;
            break;
        }
        else if(WIFEXITED(signal))
            break;
        else if(WIFSIGNALED(signal))
            break;
    }
    …
}

I want this to resume when fg command is given:

kill(tempid,SIGCONT);
while(1){
    pid_t pid_check = waitpid(pid,&signal,WNOHANG|WUNTRACED);
    if(pid_check == pid){
        if(WIFSTOPPED(signal)){
            tempid = pid_check;
            printf("Here");
            break;
        }
        else if(WIFEXITED(signal))
            break;
        else if(WIFSIGNALED(signal))
            break;
    }
}

But WIFSTOPPED keeps returning non zero so waitpid is breaking and process goes in background. I tried to search online but couldn’t find anything useful.

Answer

One thing I notice is that you’re sending the continuation signal to tempid, then monitoring pid.

Check to make sure that these are set to the same PID, although it would probably be safer and more readable to just use:

kill(pid,SIGCONT);

before entering the monitoring loop.

You might also want to consider renaming your signal variable to avoid possible clashes with the signal() function.