#include <iostream>
#pragma hdrstop
using std::cout;
using std::endl;
//---------------------------------------------------------------------------
#pragma argsused
//---------------------------------------------------------------------------
class Base {
public:
Base() { };
virtual void DisplayMessage() {
cout << "Displaying Message from an object of Base class" << endl;
};
};
//---------------------------------------------------------------------------
class DerivedFirst : public Base {
public:
DerivedFirst() { };
void DisplayMessage() {
cout << "Displaying Message from an object of DerivedFirst class" << endl;
}
};
//---------------------------------------------------------------------------
class DerivedSecond : public Base {
public:
DerivedSecond() { };
void DisplayMessage() {
cout << "Displaying Message from an object of DerivedSecond class" << endl;
}
};
//---------------------------------------------------------------------------
class DerivedThird : public Base {
public:
DerivedThird() { };
};
//---------------------------------------------------------------------------
int main()
{
// create a base class object
Base* bc = new Base();
bc->DisplayMessage();
// delete the base class object and assign it to DerivedFirst object
delete bc;
bc = new DerivedFirst();
bc->DisplayMessage();
// delete the base class object and assign it to DerivedSecond object
delete bc;
bc = new DerivedSecond();
bc->DisplayMessage();
// delete the base class object and assign it to DerivedThird object
delete bc;
bc = new DerivedThird();
bc->DisplayMessage();
delete bc;
return EXIT_SUCCESS;
}
//---------------------------------------------------------------------------
虚函数主要作用：用基类声明的指针（Base* bc），指向派生类，如果派生类中有与基类中相同的方面就调用子类的方法，如果子类没有该方面，就调用基类自身的方法。
基类中如果不加virtual 关键字，用用基类声明的指针，调用函数时只能调用基类自身的函数。
