The offsetof() macro is a compile-time construct. There is no standard-compliant way to define it, but every compiler must have some way of doing it. One example would be: #define offsetof( type, member ) ( (size_t) &( ( (type *) 0 )->member ) ) While not being a compile-time construct technically (see comments by user … Read more
From a lawyer point of view, the expression &(((struct name *)NULL)->b); should lead to UB, since you could not find a path in which there would be no UB. IMHO the root cause is that at a moment you apply the -> operator on an expression that does not point to an object. From a … Read more
Where the language standard says “undefined behavior”, any given compiler can define the behavior. Implementation code in the standard library typically relies on that. So there are two questions: (1) Is the code UB with respect to the C++ standard? That’s a really hard question, because it’s a well known almost-defect that the C++98/03 standard … Read more
Bluehorn’s answer is correct, but for me it doesn’t explain the reason for the problem in simplest terms. The way I understand it is as follows: If NonPOD is a non-POD class, then when you do: NonPOD np; np.field; the compiler does not necessarily access the field by adding some offset to the base pointer … Read more
At no point in the above code is anything dereferenced. A dereference occurs when the * or -> is used on an address value to find referenced value. The only use of * above is in a type declaration for the purpose of casting. The -> operator is used above but it’s not used to … Read more