sizeof (int) == sizeof (void*)?

Question

Is there an integer type with the same size as pointer? Guaranteed on all microarchitectures?

Answer 1

Usually sizeof(*void) depends on memory bus width (although not necessarily - pre-RISC AS/400 had 48-bit address bus but 64-bit pointers), and int usually is as big as CPU's general-purpose register (there are also exceptions - SGI C used 32-bit ints on 64-bit MIPS).

So there is no guarantee.

Answer 2

This would be true on a standard 32 bit system, but there certainly are no guarantees, and you could find lots of architectures where it isn't true. For example, a common misconception is that sizeof(int) on x86_64 would be 8 (since it's a 64 bit system, I guess), which it isn't. On x86_64, sizeof(int) is still 4, but sizeof(void*) is 8.

Answer 3

The answer seems to be "no", but if all you need is a type that can act as both, you can use a union:

union int_ptr_t {
    int i;
    void* p;
};

Answer 4

According to this Wikipedia page, in C99 your stdint.h header might declare intptr_t and uintptr_t, but then that of course requires

• C99
• A compiler implementor which has chosen to implement this optional part of the standard

So in general I think this one is tough.