Question

I want to return a unique status code to a waiting parent process from a child process through exit(), based on the execution of child’s code. If execvp fails, then the exit() is used. I assume that if execvp is successful, the command executed will send its status code.

pid=fork();
if(pid==0)
{
    if(execvp(cmdName,cmdArgs)==-1)
    {
         printf("Exec failed!\n");
         exit(K);   //K?
    }
}
waitpid(pid,&status,0);

Suppose the command passed to execvp() is “ls”, the man page says that it may return 0(success), 1 or 2(failure).

What safe unique value K can I use to indicate the return status of a child process, which won’t clash with any value returned by the command executed by execvp()?

Answer 1

For obvious reasons, there cannot be such a value of K that will never clash with the return status of any other program.

Proof: Suppose there was such a K, and you make your program call itself…