How do pointer to pointers work in C?

Question

How do pointers to pointers work in C? When would you use them?

Answer 1

When a reference to a pointer is required. For example, when you wish to modify the value (address pointed to) of a pointer variable declared in a calling function's scope inside a called function.

If you pass a single pointer in as an argument, you will be modifying local copies of the pointer, not the original pointer in the calling scope. With a pointer to a pointer, you modify the latter.