c++ - Why can't you do bitwise operations on pointer in C, and is there a way around this?

Question

I read that you can't do bitmasks on pointers, how come you can't do bitwise operations on pointers?

Is there any way to achieve the same effect?

Does the same apply to C++?

Answer 1

The reason you can't do bitwise pointer operations is because the standard says you can't. I suppose the reason why the standard says so is because bitwise pointer operations would almost universally result in undefined or (at best) implementation-defined behavior. So there would be nothing you could do that is both useful and portable, unlike simpler operations like addition.

But you can get around it with casting:

#include <stdint.h>

void *ptr1;
// Find page start
void *ptr2 = (void *) ((uintptr_t) ptr1 & ~(uintptr_t) 0xfff)

As for C++, just use reinterpret_cast instead of the C-style casts.