A SEGV by definition mean, you are trying to write to a segment outside of memory allocated to you. In the first case, you had no storage allocated, only pointers, so the first write gave you the SEGV. The second one is more difficult to detect an error. As long as you are writing to ANY memory allocated to you, you won't get a SEGV. Your pointers just happen to point to allocated memory, in this case your j[] character array. Write enough stuff there, and you'll get a SEGV there also, when you fall off the end of your allocated memory. The compiler & run time libs have no idea if you want to point to allocated memory, or where in that allocated memory you want to point, with your pointers. As long as you are pointing to allocated memory, the runtime, won't issue a SEGV (You are not writing outside of allocated memory)