解释一下C++程序
请高手帮我看看这个程序 小弟刚刚接触C++ 不是很懂 请把这个程序解释一下 这个程序很可能是错的.
请
#include <stdafx.h>
#include <iostream.h>
class Base
{public:
Base(int i) {b=i;}
void Print()=0;
protected;
int b;
};
class Derive1:public Base
{public:
Derive1(int i):Base(i){};
void Print(){cout < < "Derive1 's Print() called. " < <endl;}
};
class Derive2:public Base
{
public:
Derive2(int i):Base(i){};
viod Print(){cout < < " Derive2 's Print() called. " < <endl}
};
void fun( Base *obj ){obj-> Print();}
void main()
{Derive1 *d1=new Derive1();
Derive2 *d2=new Derive2() ;
fun(d1);
fun(d2);
}
[解决办法]
这是一个关于虚拟函数的用法实例，但是在基类里为什么printf不加虚拟virtual呢，这样的话这个程序就看不懂了。作为一个抽象基类，肯定是要声明为virtual的，否则当基类指针指向派生类时执行print就只能执行基类print了，毫无意义。
#include <stdafx.h>
#include <iostream.h>
class Base
{public:
Base(int i) {b=i;}
virtual void Print()=0; //这里加上virtual
protected;
int b;
};
class Derive1:public Base
{public:
Derive1(int i):Base(i){};
void Print(){cout < < "Derive1 's Print() called. " < <endl;}
};
class Derive2:public Base
{
public:
Derive2(int i):Base(i){};
viod Print(){cout < < " Derive2 's Print() called. " < <endl}
};
void fun( Base *obj ){ obj-> Print();}
void main()
{ Derive1 *d1=new Derive1();
Derive2 *d2=new Derive2() ;
fun(d1);
fun(d2);
}
[解决办法]
class Base
{
public:
Base(){}
Base(int i) : b(i) {};
virtual void Print() = 0; //要做纯虚函数，要添加virtual
protected:// : 不是 ;
int b;
};
class Derive1: public Base
{
public:
Derive1() {}
Derive1(int i) : Base(i){};
void Print(){cout < < "Derive1 's Print() called. " < <endl;}
};
class Derive2: public Base
{
public:
Derive2(){}
Derive2(int i) : Base(i) {};
void Print(){ cout < < " Derive2 's Print() called. " < <endl; }
// void 不是 viod , endl后面少了;
};
void fun(Base* obj){obj-> Print();}
void main()
{
//虚函数的多态性，要用基类指针.
Base* d1 = new Derive1(); //没有默认构造函数，会出错
Base* d2 = new Derive2();
fun(d1);
fun(d2);
}
