Does memory for new have to come from operator new?

Question

When considering something along the lines of

auto x = new T;

Does the Standard enforce that the memory must come from operator new- class-specific or global? i.e., there is no way a conforming implementation, given a lack of a class-specific operator new, could get the memory from anywhere except the global operator new?

Answer 1

I think you have it the wrong way round.

The expression new T always consists of two steps:

1. A suitable operator new is searched for. If one exists in the class T, that one is taken, otherwise the global one is taken. The global one always exists, as this is mandated by the standard (so you can never "define" it (since it is already defined), but you can replace it).

   You can say ::new T to always pick the global operator new unconditionally.

2. Once the allocation function has been called and succeeded, the object is constructed in that memory.

If you say new (a, b, c) T, then the same happens, only that in step 1 we are now looking for an operator new overload with the appropriate signature.