多重继承内存地址问题

 

[cpp] view plaincopy

#include <iostream.h>
class ClassA
{
public:
virtual ~ ClassA(){};
virtual void FunctionA(){};
};
class ClassB
{
public:
virtual void FunctionB(){};
};
class ClassC : public ClassA,public ClassB
{public:
};
void main(){
ClassC aObject;
ClassA* pA=&aObject;
ClassB* pB=&aObject;
ClassC* pC=&aObject;
cout<<pA<<endl;
cout<<pB<<endl;
cout<<pC<<endl;
}

假设aObject的地址是 xxx.
那么：
pA=xxx
pB=xxx + 4(如果ClassA里面多一个 int a；那么这个地址将会变成xxx+8)
pC=xxx

ClassA里面定义了虚函数，所以会有一个虚函数表指针(4 byte)。ClassA的总大小为4 byte. 同理，ClassB的总大小为4 byte.
ClassC从ClassA, ClassB继承来的，在内存中ClassA, ClassB顺序排列。ClassC的总大小为8 byte.

“ClassB* pB=&aObject;”这个隐式转换会得到ClassB类的地址。

class CA{
public:
	//virtual ~CA(){};
	//virtual void f(){cout<<"CA::f"<<endl;}
	int m1;
};
class CB{
public:
	int m2;
	//virtual void f(){cout<<"CA::f"<<endl;}
};
class CC: public CA,public CB{
public:
	int m3;
};

int main(){
	CC* pC=new CC;
	CB* pB=dynamic_cast<CB*>(pC);
	CA* pA=dynamic_cast<CA*>(pC);
	if(pC==pB)
		cout<<"equal"<<endl;
	else
		cout<<"not equal"<<endl;
	if(pC==pA)
		cout<<"equal"<<endl;
	else
		cout<<"not equal"<<endl;
	if(int(pC)==int(pB))
		cout<<"equal"<<endl;
	else
		cout<<"not equal"<<endl;
	if(int(pC)==int(pA))
		cout<<"equal"<<endl;
	else
		cout<<"not equal"<<endl;
	system("pause");
	return 1;
}

输出是：equal  equal  not equal  equal