[C/C++] C++類別繼承筆記(1)

#include <iostream>

using namespace std;

class A
{
    public:
    A(string s)
    {
        cout<<"construct A:"<<s<<endl;
        a = s;
    }
    virtual void displayA() //=0 純虛擬不能實體化
    {
        cout<<"dispalyA"<<endl;
    }
    
    protected:
    string a;
};

class B:public A
{
    public:
    B():A("before B"){cout<<"construct B"<<endl;}
    
    void displayA()         //也是virtual 不需再加
    {
        cout<<"dispalyB"<<endl;
    }
    
    void dispalyB()
    {
        cout<<a<<endl;
    }
};
class C:public B
{
    void displayA()          //也是virtual 不需再加
    {
        cout<<"dispalyC"<<endl;
    }
};
int main()
{
   cout << "Hello World" << endl; 
   A ca("test");    //可實體化
   ca.displayA();
   A *pa;
   B cb;
   pa = &cb;
   pa->displayA();  //虛擬函式會往子class找有實作的
   return 0;

結果:
Hello World
construct A:test
dispalyA
construct A:before B
construct B
dispalyB