C++ 中的临时对象在哪里分配？

Question

SomeClass a, b, c;
SomeClass foo();
SomeClass a = (b + c); //Where is the object (b + c) allocated?
SomeClass a = foo(); //Where is the returned value of foo() allocated?

My guess is that they are allocated on the heap because I read that temporary objects are destroyed at the end of the expression(;).

It makes sense to me because the move constructor could be implemented by stealing the pointer of the temporary object on the heap.

Answer 1

If created at all (consider optimizations), they're in automatic storage . Ie the stack.

Answer 2

Generally, if there's a destination for the temporary object, it can be created there. Even stronger, that can be true even if the temporary has a different type: Foo f = transmogrify(Bar()); - the Bar() temporary can probably steal the storage needed for f .

There's a theoretical model when destructors run, but often that's not observable behavior and therefore optimizable. Ie many dtors can run early.