In which situations is the C++ copy constructor called?

Question

I know of the following situations in c++ where the copy constructor would be invoked:

1. when an existing object is assigned an object of it own class

Answer 1

Situation (1) is incorrect and does not compile the way you've written it. It should be:

MyClass A, B;
A = MyClass(); /* Redefinition of `A`; perfectly legal though superfluous: I've
                  dropped the `new` to defeat compiler error.*/
B = A; // Assignment operator called (`B` is already constructed)
MyClass C = B; // Copy constructor called.

You are correct in case (2).

But in case (3), the copy constructor may not be called: if the compiler can detect no side effects then it can implement return value optimisation to optimise out the unnecessary deep copy. C++11 formalises this with rvalue references.