In what cases does C++ automatically invoke the copy constructor?

Automatic invocation of the copy constructor in C++ occurs in the following cases:

• When initializing an object with another object of the same type, for example:

  MyClass a;
  MyClass b = a; // copy constructor is called
  

• When passing an object by value to a function:

  void func(MyClass obj); // calling func(a) will invoke the copy constructor
  

• When returning an object by value from a function (before compiler optimizations):

  MyClass func() {
      MyClass a;
      return a; // may invoke the copy constructor
  }
  

• When initializing an object in the initialization list of another object.

If the copy constructor is not explicitly defined, the compiler will generate it automatically if possible.