C standard compliant way to access null pointer address?

Question

In C, deferencing the null pointer is Undefined Behavior, however the null pointer value has a bit representation that in some architectures make it points to a val

Answer 1

As OP has correctly concluded in her answer to her own question:

There is no standard way because there are no (architectural) address in the C standard document. This is true for every (architectural) address, not only the int2ptr(0) one.

However, a situation where one would want to access memory directly is likely one where a custom linker script is employed. (I.e. some kind of embedded systems stuff.) So I would say, the standard compliant way of doing what OP asks would be to export a symbol for the (architectural) address in the linker script, and not bother with the exact address in the C code itself.

A variation of that scheme would be to define a symbol at address zero and simply use that to derive any other required address. To do that add something like the following to the SECTIONS portion of the linker script (assuming GNU ld syntax):

_memory = 0;

And then in your C code:

extern char _memory[];

Now it is possible to e.g. create a pointer to the zero address using for example char *p = &_memory[0]; (or simply char *p = _memory;), without ever converting an int to a pointer. Similarly, int addr = ...; char *p_addr = &_memory[addr]; will create a pointer to the address addr without technically casting an int to a pointer.

(This of course avoids the original question, because the linker is independent from the C standard and C compiler, and every linker might have a different syntax for their linker script. Also, the generated code might be less efficient, because the compiler is not aware of the address being accessed. But I think this still adds an interesting perspective to the question, so please forgive the slightly off-topic answer..)