多继承指针转化的问题

标签：c++   多继承   

多继承的指针转化跟数据在内存的布局有极大的关系。目前，用msvc11和gcc4.8.3去测试指针转化之后的结果。发现只要不涉及编译增加虚表指针的情况下，派生类的地址多数是和继承列表的首个父类地址相同。当然会有其他问题影响到布局的指针转化。此次要提的内容是，别使用c_style指针转化。正确的指针转化来自于：dynamic_cast/static_cast。

编译器内部生成的指针对象有某个反射机制，能从父类指针正确的映射出派生类地址。无论是普通继承还是virtual继承。具体的内存布局我还要看完书才行，待续。

编译器的实现真是太有学问啦，同时也影响着我们使用这门语言。为了未来几十年能在游戏引擎有所作为，必须吃透C++/C、数学和计算机图形学应用方向等。

#include <cstdio>
#include <iostream>
#include <string>
#include <cstdarg>




class A
{
public:
	A()
	{
		i = 10;
	};
	~A(){};
	virtual void display()
	{

	}
	int i;
};

class B
{
public:
	virtual void display()
	{

	}
	int j;
};

class C :public A,public B
{
public:
	int i;
	int k;
private:
	
	
};

class D:virtual public A
{
public:
	int di;
	virtual void display() override
	{

	}
private:

};

class  E :virtual public A
{
public:
	int ei;
	virtual void display() override
	{

	}

private:

};

class F : public D,public E
{
public:
	int fi;

	virtual void display() override
	{

	}

private:

};








int main(int argv, char **argc)
{


	C * pC = new C();
	B * pB = dynamic_cast<B*>(pC);
	A * pA = dynamic_cast<A*>(pC);
	B * pB_s = static_cast<B*>(pC);
	A * pA_s = static_cast<A*>(pC);
	C * pCB_D = dynamic_cast<C*>(pB);
	C * pCA_D = dynamic_cast<C*>(pA);
	C * pCB_S = static_cast<C*>(pB);
	C * pCA_S = static_cast<C*>(pA);

	pC->i = 100;
	printf("%d\n",pA->i);
	

	printf("pC = %d,pB_d = %d,pA_d = %d,pB_s = %d,pA_s = %d\n", pC, pB, pA, pB_s, pA_s);

	printf("pCB_D = %d,pCA_D = %d,pCB_S = %d,pCA_S = %d\n", pCB_D, pCA_D, pCB_S, pCA_S);

	F * pF = new F();

	D * pD = dynamic_cast<D*>(pF);
	E * pE = dynamic_cast<E*>(pF);
	D * pD_s = static_cast<D*>(pF);
	E * pE_s = static_cast<E*>(pF);

	F * pFD_D = dynamic_cast<F*>(pD);
	F * pFE_D = dynamic_cast<F*>(pE);
	F * pFD_S = static_cast<F*>(pD);
	F * pFE_S = static_cast<F*>(pE);

	printf("pF = %d,pD_d = %d,pE_d = %d,pD_s = %d,pE_s = %d\n", pF, pD, pE, pD_s, pE_s);
	
	printf("pFD_D = %d, pFE_D = %d,pFD_S = %d, pFE_S = %d\n", pFD_D, pFE_D, pFD_S, pFE_S);
	
	return 0;
}

多继承指针转化的问题

标签：c++   多继承   

原文地址：http://blog.csdn.net/jingzhewangzi/article/details/41521759