C++继承

#include<iostream>
using namespace std;
 
struct IA
{
    virtual void funInIA() = 0;
};
 
struct IB
{
    virtual void funInIB() = 0;
};
 
struct C : public IA, public IB
{
    virtual void funInIA()
    {
        cout << "funInIA" << endl;
    }
 
    virtual void funInIB()
    {
        cout << "funInIB" << endl;
    }
};
 
int main()
{
    IA* pIA = new C;
    pIA->funInIA();
 
    IB* pIB = (IB*)(void*)(pIA);
    //IB* pIB = new C;
    pIB->funInIB();
 
    delete pIA;
    return 0;
}

上面代码输出：（偏移，欺骗，误打误撞）

funInIA
funInIA

如果将Line 23换成：

IB* pIB = (IB*)(C*)(pIA);
or
IB* pIB = dynamic_cast<IB*>(pIA);

so 代码输出：

funInIA
funInIB

如果，代码如下：

#include<iostream>
using namespace std;
 
struct IA
{
    virtual void funInIA() = 0;
};
 
struct IB
{
    virtual void funInIB() = 0;
};
 
struct C : public IA, public IB
{
    virtual void funInIA()
    {
        cout << "C - funInIA" << endl;
    }
 
    virtual void funInIB()
    {
        cout << "C - funInIB" << endl;
    }
};
 
 
struct D : public IA, public IB
{
    virtual void funInIA()
    {
        cout << "D - funInIA" << endl;
    }
 
    virtual void funInIB()
    {
        cout << "D - funInIB" << endl;
    }
};
 
IA* CreateInstance()
{
    return new C;
    //or //return new D;
}
 
int main()
{
    IA* pIA = CreateInstance();
    pIA->funInIA();
 
    IB* pIB = (IB*)(pIA);
    pIB->funInIB();
 
    delete pIA;
    return 0;
}

以上输出：

C - funInIA
C - funInIA

无论将代码line 52 改成

IB* pIB = (IB*)(D*)(pIA);
or
IB* pIB = (IB*)(C*)(pIA);
代码都会输出：

C - funInIA
C - funInIB

 如果子类重新了父类函数，又想调用父类，则可以：
Derive-Instance.Base::print();

没有虚析构函数，继承类没有析构
//Example:  non- virtual destructors for dynamically allocated objects.
 
#include <iostream.h>
#include <string.h>
class Thing
{ public:
　　　　　　virtual void what_Am_I( ) {cout << "I am a Thing.
";}
　　　　　　~Thing(){cout<<"Thing destructor"<<endl;}
};
class Animal : public Thing
{  
public:
　　　　　　virtual void what_Am_I( ) {cout << "I am an Animal.
";}
15　　　　　　 ~Animal(){cout<<"Animal destructor"<<endl;}
};
int main( )
{
   Thing *t =new Thing;      
   Animal*x = new Animal;
   Thing* array[2];
   array[0] = t;                                // base pointer
   array[1] = x;               
    for (int i=0; i<2; i++)  array[i]->what_Am_I( ) ;
   delete array[0];
   delete array[1];
   return 0;
}

以上代码输出:

I am a Thing.
I am an Animal.
Thing destructor
Thing destructor
当把父类析构函数加上virtual后，以上代码输出:

I am a Thing.
I am an Animal.
Thing destructor
Animal destructor
Thing destructor