et, bonne lecture :
If command is NULL and the command interpreter is found, the function returns a nonzero value. If the command interpreter is not found, it returns 0 and sets errno to ENOENT. If command is not NULL, system returns the value that is returned by the command interpreter. It returns the value 0 only if the command interpreter returns the value 0. A return value of ? 1 indicates an error, and errno is set to one of the following values:
(trouvé dans la msdn en 2 secondes !)