How to check if char pointer is a constant!?

Hi everybody,

I have some function, say
void empty(char *p) { p[0] = '\0'; }

If I call it like this empty("Hello") it will segfaults since "Hello"
is put in readonly section of the program. Is there a way to check for
this?! Maybe some nasty gcc extension!?

Regards,

-- 
"Do or do not. There is no try"
  Yoda Master