C++之踏入多态

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一.先考虑在继承的时候基类与派生类的初始化顺序和一个类中的数据成员的初始化顺序

#include<iostream>
using namespace std;

class A
{
public:
	A(int x=0):m_data(x)
	{
  cout<<"Constructor A!!!\n";
	}
private:
	int m_data;
};

class B
{
public:
	B(int x=0,int y=0):data(y)
	{
       cout<<"Constructor B!!!\n";
	}
private:
	int data;
};

class C:public A,public B
{
public:
	C(int x=0,int y=0,int z=0):A(x),B(y),b(z),a(y)
	{
    cout<<"Constructor C!!!\n";
	}
private:
	int c_data;
	B b;
	A a;
};
void  main()
{
   C b;

}

二.C++中钻石类的继承

下面就是一个钻石类，因为最base 类会在最低的继承类中存在两种从 derived 继承来的版本，这样就造成了数据的不准确

#include<iostream>
using namespace std;

class A
{
public:
	A(int x=0):m_data(x)
	{
   cout<<"constructor A\n";
	}
	void show ()
	{
		cout<<m_data<<"\n";
	}

private:
	int m_data;
};

class B:virtual public A
{

public:
	B(int x=0):A(x)
	{
	cout<<"constructor B\n";
	}

	void show()
	{
		show();
	cout<<m_data<<"\n";
	}
private:
};

class C:virtual public A
{
public:
	C(int x=0):A(x)
	{
 cout<<"constructor C\n";
	}
};
class D:public B,public C
{
public:
    D(int x=0):B(x),C(x)
	{

  cout<<"constructor D\n";
	}
};
void main()
{
	D d(1);

<span style="font-size:18px;">}</span>

#include<iostream>
using namespace std;

class A
{
public:
	A(int x=0):m_data(x)
	{
		cout<<"constructor A\n";
	}
   virtual	void show ()
	{
		cout<<"A:: "<<m_data<<"\n";
	}
	virtual A* Ret()//VC 6.0 不支持这种,vs 2008支持其实这个函数符合3同，返回值，函数名，参数相同
	{
		    cout<<"A::  Ret Fuction!!!\n";
			return this;
	}
	
	virtual ~A()//在存在指针数据的类中，把析构函数设计成虚函数更能体现出价值
	{
		cout<<"Destructor A!!!";
	}
private:
	int m_data;
};

class B: public A
{
	
public:
	B(int x=0,int y=0):A(x),data(y)
	{
		cout<<"constructor B\n";
	}
	void show()
	{
	cout<<"B:: "<<data<<"\n";
	}

	B* Ret()
	{
		cout<<"B::  Ret Fuction!!!\n";
		return this;
	}
   ~B()
   {
	  cout<<"Destructor B!!!";
   }
private:
	int data;
};

void main()
{
	A a;
	B b(1,2);
	a=b;
	a.show();
	a.Ret();
	cout<<"\n\n";
	//以下可以实现多态都是依靠赋值兼容规则借助指针和引用实现
	A *ptr=&b;
	ptr->show();
    ptr->show();

	A &p=b;
	p.show();
    p.Ret();
}

C++之踏入多态

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原文地址：http://blog.csdn.net/kai8wei/article/details/46688953