In C, all arguments are passed by value. All of them.  Every  time.

If the argument is a pointer, its value (i.e., the address it contains) is
passed by value.  That means that:
(a) you cannot change in the function what the caller's pointer is pointing at,
    since you're operating on a copy of the pointer
(b) but you can change the memory pointed at by your copy of the pointer,
    because it's the same memory that the caller's pointer is pointing at