《Inside the C++ Object Model》关于基类与派生类的Tips

近来阅读《Inside the C++ Object Model》,里边讲到，在C++中多态只存于public class体系中，且只有通过pointer和reference来间接处理。

#include <iostream>

using std::cout;
using std::endl;

class Base
{
public:
	virtual void printf(void)
	{
		cout<< "Base printf"<< endl;
	}
};

class Derv : public Base
{
public:
	virtual void printf(void)
	{
		cout<< "Derv printf"<< endl;
	}
};

int main(int argc, char** argv)
{
	Base* pBase = new Base();
	Derv* pDerv = new Derv();
	pBase = pDerv;
	pBase->printf();

	cout<<"-------------------------"<< endl;

	Base* pBase2 = new Derv();
	pBase2->printf();

	cout<<"-------------------------"<< endl;

	Base base;
	Derv derv;
	base = derv;
	base.printf();

	cout<<"-------------------------"<< endl;

	Derv derv2;
	Base &base2 = derv2;
	base2.printf();

	getchar();
	return 0;
}

结果如下：

 可见对象base并未调用派生类中的printf()函数，而是继续使用基类的函数。

 不知在哪见过，调用printf()函数时，指向它的this指针属于谁，那么就调用谁的printf()；具体内容待找到后补上。

 例子：

#include <iostream>

using std::cout;
using std::endl;

class Base
{
public:
	Base(): m_nData(1){}

	virtual void printf(void)
	{
		cout<< m_nData<< endl;
	}

private:
	int m_nData;
};

class Derv : public Base
{
public:
	Derv() : m_nData(2){}
	virtual void printf(void)
	{
		cout<< m_nData<< endl;
	}

private:
	int m_nData;
};

int main(int argc, char** argv)
{
	Base* pBase = new Base();
	Derv* pDerv = new Derv();
	pBase = pDerv;
	pBase->printf();

	cout<<"-------------------------"<< endl;

	Base* pBase2 = new Derv();
	pBase2->printf();

	cout<<"-------------------------"<< endl;

	Base base;
	Derv derv;
	base = derv;
	base.printf();

	cout<<"-------------------------"<< endl;

	Derv derv2;
	Base &base2 = derv2;
	base2.printf();

	getchar();
	return 0;
}

结果如下：