I have a question regarding the C++ Standard.
Suppose you have a base class with user defined copy constructor and assignment operator. The derived class uses the implicit one generated by the compiler.
Does copying / assignment of the derived class call the user defined copy constructor / assignment operator? Or do you need to implement user defined versions that call the base class?
Thank you for your help.
If a derived class does not declare a copy constructor, and implicit one will be declared (12.8/4 "Copying class objects") - even if the base class has a user-delcared and defined copy constructor. If the base class has a user-defined copy constructor in this case, that base class sub-object is copied using that user-defined copy ctor (12.8/8).
Similarly for copy assignment operators (12.8/10 and 12.8.13).
So you do not necessarily need to implement user defined versions that call the base class if the derived class doesn't need a user-defined copy ctor or copy assignment operator for 'its own stuff'. However, if the derived class does declare and define its own copy ctor/copy assignment operator, then those user-defined implementations are responsible for doing the right thing as far as the base class sub-object is concerned - that is no longer handled by the compiler automatically.
Only if the derived class has an explicitly defined operator function. Otherwise, the op function of the parent class is called. Otherwise, the implicit C++ one is called.
来源：https://stackoverflow.com/questions/2779316/behaviour-of-the-implicit-copy-constructor-assignment-operator