this指针再探讨：究竟绑定谁？

        在深入MFC之前，应该先搞懂最简单的this指针。我们先看简单的程序：

 

#include <iostream>
using namespace std;
 
class Base
{
public:
    void fun()
	{
		cout << "Base fun" << endl;
	}
};
 
class Derived : public Base
{
public:
    void fun()
	{
		cout << "Derived fun" << endl;
	}
};
 
int main()
{
 
	Base b, *pB;
	pB = &b;
	pB->fun();
 
	Derived d;
	pB = &d;
	pB->fun();
 
	return 0;
}

       结果为：

 

Base fun
Base fun

       改为虚函数，如下：

 

#include <iostream>
using namespace std;
 
class Base
{
public:
    virtual void fun()
	{
		cout << "Base fun" << endl;
	}
};
 
class Derived : public Base
{
public:
    virtual void fun()
	{
		cout << "Derived fun" << endl;
	}
};
 
int main()
{
 
	Base b, *pB;
	pB = &b;
	pB->fun();
 
	Derived d;
	pB = &d;
	pB->fun();
 
	return 0;
}

      结果为：

 

Base fun
Derived fun

      下面我们来看看this指针，程序如下：

 

#include <iostream>
using namespace std;
 
class Base;
Base *pB;
 
class Base
{
public:
	Base()
	{
		pB = this;
		cout << "Base Constructor" << endl;
	}
 
    void fun()
	{
		cout << "Base fun" << endl;
	}
};
 
class Derived : public Base
{
public:
	Derived()
	{
		cout << "Derived Constructor" << endl;
	}
 
    void fun()
	{
		cout << "Derived fun" << endl;
	}
};
 
int main()
{
	Base b;
	pB->fun();
 
	Derived d;
	pB->fun();
 
	return 0;
}

       程序结果为：

 

Base Constructor
Base fun
Base Constructor
Derived Constructor
Base fun
       

      改为虚函数，程序如下：

 

#include <iostream>
using namespace std;
 
class Base;
Base *pB;
 
class Base
{
public:
	Base()
	{
		pB = this;
		cout << "Base Constructor" << endl;
	}
 
    virtual void fun()
	{
		cout << "Base fun" << endl;
	}
};
 
class Derived : public Base
{
public:
	Derived()
	{
		cout << "Derived Constructor" << endl;
	}
 
    virtual void fun()
	{
		cout << "Derived fun" << endl;
	}
};
 
int main()
{
	Base b;
	pB->fun();
 
	Derived d;
	pB->fun();
 
	return 0;
}

        结果为：

 

Base Constructor
Base fun
Base Constructor
Derived Constructor
Derived fun

       下面的这个程序颇似MFC程序：

 

#include <iostream>
using namespace std;
 
class Base
{
public:
	Base *pB;
 
	Base()
	{
		pB = this;
		cout << "Base Constructor" << endl;
	}
 
	virtual void fun()
	{
		cout << "Base fun" << endl;
	}
};
 
class Derived : public Base
{
public:
	Derived()
	{
		cout << "Derived Constructor" << endl;
	}
 
	virtual void fun()
	{
		cout << "Derived fun" << endl;
	}
};
 
Derived d;
 
Base *getPointer()
{
	return d.pB;
}
 
int main()
{
	Base *p = getPointer();
	p->fun();
 
	return 0;
}

      结果为：

 

Base Constructor
Derived Constructor
Derived fun

 

      如果要深入理解MFC, 那么搞懂上面这些简单的程序是很有必要的。