why we require uint64_t when unsigned long is available ? [duplicate]

Question

I just wanted to know, Why we need to have uint64_t which is actually a typedef of unsigned long , when unsigned long is anyway available. Is it only for make the name short or any other reason ?

Answer 1

The reason should be pretty obvious; it's a guarantee that there is 64 bits of precision. There is no such guarantee for unsigned long.

The fact that on your system it's a typedef, just means that on your system unsigned long is 64 bits. That's not true in general, but the typedef can be varied (by the compiler implementors) to make the guarantee for uint64_t.

Answer 2

It's not always a typedef for unsigned long, because unsigned long is not universally 64 bit wide. For example, on x64 Windows, unsigned long is 32 bit, only unsigned long long is 64 bit.