When to use system() and when to use execv*()?
Well, the other answers are mostly correct.
System, while not only forks and then execs, it doesn't exec your process, it runs the default shell, passing your program as an argument.
So, unless you really want a shell (for parameter parsing and the like) it is much more efficient to do something like:
int i = fork();if ( i != 0 ) { exec*(...); // whichever flavor fits the bill} else { wait(); // or something more sophisticated}
The exec family of functions will replace the current process with a new one, whilst system will fork off the new process, and then wait for it to finish. Which one to use depends on what you want.
Since you're doing this in a loop, I guess you don't want to replace the original process. Therefore, I suggest you try to go with system.