If you are adding things like friend operators to a class like this:

MyClass

you can click "Add definition to class.cpp" to create a definition. The definition incorrectly looks like this:

bool MyClass::operator==(const MyClass& lhs, const MyClass& rhs)
{

}

The MyClass:: part should not be there, as a friend function can be declared inside the scope of the class but is not a member function of that class.