demo of virtual functions

lectures/26_inheritance/virtual.cpp

@@ -0,0 +1,67 @@
+#include <iostream>
+
+class A
+{
+public:
+	void print(){
+		std::cout << "A" << std::endl;
+	}
+};
+
+class B: public A
+{
+public:
+	// virtual void print(){
+	void print(){
+		std::cout << "B" << std::endl;
+	}
+};
+
+class C: public B
+{
+public:
+	void print(){
+		std::cout << "C" << std::endl;
+	}
+};
+
+class D: public C
+{
+public:
+	void print(){
+		std::cout << "D" << std::endl;
+	}
+};
+
+int main(){
+	// initialize base class pointer with a derived class object.
+	A* pA = new B;
+	// which print is getting called?
+	// if no virtual, decide by pointer type.
+	pA->print();
+
+	// which print is getting called?
+	// if no virtual, decide by pointer type.
+	// if base is marked as virtual, decide by object type.
+	B* pB = new C;
+	pB->print();
+	// which print is getting called?
+	// pointer and object same type, just call its local member function.
+	pB = new B;
+	pB->print();
+	// which print is getting called?
+	// if no virtual, decide by pointer type.
+	// if base is marked as virtual, decide by object type.
+	C c;
+	pB = &c;
+	pB->print();
+
+	// which print is getting called?
+	// if no virtual, decide by pointer type.
+	// if base is marked as virtual, decide by object type.
+	// also, virtual can be inheritated, even if the derived one doesn't use the virtual keyword.
+	C* pC = new D;
+	pC->print();
+
+	return 0;
+}