Yes, the size of a pointer is platform dependent. More specifically, the size of a pointer depends on the target processor architecture and the "bit-ness" you compile for.
As a rule of thumb, on a 64bit machine a pointer is usually 64bits, on a 32bit machine usually 32 bits. There are exceptions however.
Since a pointer is just a memory address its always the same size regardless of what the memory it points to contains. So a pointer to a float, a char or an int are all the same size.
