Question

Which line is the correct (best) way for defining a pointer?

typedef ptrdiff_t pointer; // pointers are ptrdiff_t.

          -- or --

typedef void* pointer; // pointers are void*.


pointer ptr = malloc(1024);

Answer 1

Pointers in C are of type T* where T is the type pointed to; void* is the generic pointer type. Usually, you let C implicitly convert void* to something useful, e.g.

char *buffer = malloc(1024);

ptrdiff_t is the type returned by the subtraction of two pointers, e.g.

ptrdiff_t d = write_ptr - buffer;
// now you know the write_ptr is d bytes beyond the start of the buffer

ptrdiff_t is an integral type, not a pointer type; you cannot use the indirection operator * on it. (Nor can you meaningfully use it on a void*, by the way.)

Had you wanted to store a pointer in an integer type, uintptr_t would have been appropriate.