Hi Fan Lu, > And in my opinion, the constructor of base class (if defined) will > always be invoked in spite of whether the derived class has its own > constructor, Correct. And if the base class constructor is not explicitly identified in the derived class's explicit constructor, the base class default constructor will be used. > but the copy constructor and assignment operator in base class(if > defined) will not be invoked if the derived class has its own. > Is it right? Re: copy constructor... Correct, the derived class explicit copy constructor needs to explicitly call the base class copy constructor (assuming that is the desired behavior). OTHERWISE, the base class default constructor will be used if left implicit. Re: assignment operator... Correct, the derived class explicit assignment operator needs to explicitly call the base class assignment, assuming the desired behavior is that the base class assignment operator also be called. OTHERWISE, the base class will have the same member variable values that it had before the assignment operator call (assuming nothing else has changed the state of those variables in the derived class assignment operator). You may want to take a look into using the std::swap technique to maintain object state integrity during the assignment operation. (q.v. Herb Sutter "C++ Coding Standards" on std::swap, assignment operator, and "never fail".) Sincerely, --Eljay
