virtual-functions

Why do I sometimes see in C++ examples when talking about subclassing / inheritance, the base class has virtual keyword and sometimes the overridden function has also the virtual keyword, why it's necessary to add to the subclass the virtual key word sometimes? For example: class Base { Base(){}; virtual void f() ...... } }; class Sub : public Base { Sub(){}; virtual void f() ...new impl of f() ... } }; It is not necessary, but it helps readability if you only see the derived class definition. §10.3 [class.virtual]/3 If a virtual member function vf is declared in a class Base and in a class

I have been reading about Virtual functions and found, VF are used in polymorphism of an inherited class. So , if a class and derived class both have the same function name, VF binds the appropriate function to the function call. i.e. If the function in question is designated virtual in the base class then the derived class's function would be called. If it is not virtual, the base class's function would be called. In Java by default: all functions are Virtual C++: Non-virtual and can be made Virtual in Java by using final, private access modifier while in C++ using Virtual keyword to make a

If the virtual function table is the same for all objects of the class, then why can't the pointer to that table (vfptr) be static and be shared across all the objects? The vtable is essentially static. But you need a vptr member actually inside the object to do virtual dispatch and other RTTI operations. On a vptr implementation, this C++ code: class Base { public: virtual void f(); }; class Derived : public Base { public: virtual void f(); }; may act similarly to something like this: class Base { public: Base::Base() : m_vptr(&Base_vtab) {} Base::Base(const Base& b) : m_vptr(&Base_vtab) {}

QUESTION 1) class Base { Base(std::string name); virtual std::string generateName(); } class Derived : Base { Derived(); virtual std::string generateName(); } here comes the question : what method will be called on generateName() ? Derived :: Derived : Base(generateName()) { //what method will be called on generateName() ? } QUESTION 2) how should i make it? if the default constructor must accept a parameter, but i need to generate that parameter in the Derived constructor? First, the solution: use a static member function or a nonmember function. As for the behavior, Derived::generateName()

Consider this simple situation: A.h class A { public: virtual void a() = 0; }; B.h #include <iostream> class B { public: virtual void b() {std::cout << "b()." << std::endl;}; }; C.h #include "A.h" #include "B.h" class C : public B, public A { public: void a() {std::cout << "a() in C." << std::endl;}; }; int main() { B* b = new C(); ((A*) b)->a(); // Output: b(). A* a = new C(); a->a(); // Output:: a() in C. return 0; } In other words: - A is a pure virtual class. - B is a class with no super class and one non-pure virtual function. - C is a subclass of A and B and overrides A's pure virtual