unsigned long long conflict with uint64_t? [duplicate]

Answer 1

So unsigned long long is the same as uint64_t in the 32-bit compilation but not in 64-bit compilation?

Yes.

In 32-bit mode, most likely long is 32 bits and long long is 64 bits. In 64-bit mode, both are probably 64 bits.

In 32-bit mode, the compiler (more precisely the <stdint.h> header) defines uint64_t as unsigned long long, because unsigned long isn't wide enough.

In 64-bit mode, it defines uint64_t as unsigned long.

It could have defined it as unsigned long long in both modes. The choice is arbitrary; all that's required is that it has to be a 64-bit type.

In general, each of the integer types defined in <stdint.h> is a typedef for some predefined type with the appropriate characteristics. You can't assume that any of them are distinct from the predefined types.

Answer 2

This is from stdint.h for GCC 4.8:

#if __WORDSIZE == 64
typedef unsigned long int   uint64_t;
#else
__extension__
typedef unsigned long long int  uint64_t;
#endif

So:

So unsigned long long is the same as uint64_t in the 32bit compliation but not in 64 bit compliation?

Yes.