virtual function, C++ (gcc)

virtual function

//g++  5.4.0

#include <iostream>
using std::cout ;
using std::string;

struct Base{
public:
    // virtual function
    virtual void func() {
        cout<<"Hello World\n";
    }
    
    // pure virtual function
    virtual void say(string message) = 0;
};

class A : public Base{
public:
    
    // override Base::func, and mark "final"(can not be overrride)
    void func() final{
        cout<<"A func\n";
    }
    
    // override Base::say
    void say(string message) override{
        cout<<message<<'\n';
    }
    
    // base class haven't "test" to override
    //void test() override;

};

class B : public A{
    string name;
public:
    B(const char* name):name(name){}
    
    // A::func is marked "final" cannot be override
    //void func() override;
    
    // override A::say
    void say(string message) override{
        cout<<name<<" say "<<message<<'\n';
    }
};

int main()
{
    //Base base; // error: Base is abstract class
    Base* a = new A();
    Base* b = new B("B");
    
    a->func();
    a->say(string("Hi"));
    b->say(string("Hi"));
    
    a->Base::func();
    b->Base::func();
}


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