Is memcpy of a pointer the same as assignment?

Question

Introduction: This question is part of my collection of C and C++ (and C/C++ common subset) questions regarding the cases where pointers object with strictly ide

Answer 1

You have proven that it seems to work on a specific implementation. That doesn't mean that it works in general. In fact, it is undefined behavior where one possible outcome is exactly "seems to work".

If, we go back to the MS-DOS era we had near pointers (relative to a specific segment) and far pointers (containing both a segment and an offset).

Large arrays were often allocated in their own segment and only the offset was used as a pointer. The compiler already knew what segment contained a specific array, so it could combine the pointer with the proper segment register.

In that case, you could have two pointers with the same bit-pattern, where one pointer pointed into an array segment (pa) and another pointer pointed into the stack segment (pb). The pointers compared equal, but still pointed to different things.

To make it worse, far pointers with a segment:offset pair could be formed with overlapping segments so that different bit-patterns still pointed to the same physical memory address. For example 0100:0210 is the same address as 0120:0010.

The C and C++ languages are designed so that this can work. That's why we have rules that comparing pointers only works (gives a total order) within the same array, and that pointers might not point to the same thing, even if they contain the same bit-pattern.