Are all pointers derived from pointers to structure types the same?

Question

The Question

The question of whether all pointers derived from pointers to structure types are the same, is not easy to answer. I find it to be a significant quest

Answer 1

My answer is "no."

There is no wording in any standard of C that I'm aware of which suggests otherwise. The fact that all pointers to structure types have the same representation and alignment requirements has no bearing on any derived type.

This makes complete sense and any other reality would seem to be inconsistent. Consider the alternative:

Let's call the alignment and representation requirements for pointers to structure types "A". Suppose that any "recursively derived type" shares the requirements "A".

Let's call the alignment and representation requirements for pointers to union types "B". Suppose that any "recursively derived type" shares the requirements "B".

Let's suppose that "A" and "B" are not the same[1]. Furthermore, let's suppose that they cannot be satisfied at the same time. (A 4-byte representation and an 8-byte representation, for example.)

Now derive a type from both:

1. A type with requirements "A"
2. A type with requirements "B"

Now you have a type whose requirements are impossible to satisfy, because it must satisfy "A" and "B", but they cannot both be satisfied at once.

Perhaps you're thinking of derived types as having a flat lineage all the way back to a single ancestor, but that's not so. Derived types can have many ancestors. The standard definition of "derived types" discusses this.

[1] While it might seem unreasonable, unlikely and silly, it's allowed.