帮忙看看错在哪里！

[talkingmute]

#include<iostream.h>
class ca
{
private:
int a1;
public:

virtual f(){}
};
class cb:public ca
{
private:
int b1;
public:

f(){return b1}
};
main()
{
ca *p;
cb *p1=(cb *)p;
p1->m_b1=0;
p1->f();
return 0;
}

[zhouqingyuan]

楼主大约想表现一下多态的特性，再写一下。
#include<iostream.h>
class ca
{
private:
int a1;
public:
ca(int x=1):a1(x){}
virtual void f(){cout<<a1;}
};
class cb:public ca
{
private:
int b1;
public:
cb(int x=0):b1(x){}
virtual void f(){cout<<b1<<endl;}
};
class cc:public ca
{
private:
int c1;
public:
cc(int x=2):c1(x){}
virtual void f(){cout<<c1<<endl;}
};
int main()
{
ca *p=new cb;
p->f();
p=new cc;
p->f();
return 0;
}

[gundamboy]

用了new,最好还是在后面用delete吧

[bmwboy]

哪个是对象？对象都没一个怎么初始化

[zhouqingyuan]

ca *p;//你的对象都没有产生，

[zhouqingyuan]

你写的错误比较多，大致改成下面的样子，楼主还得把书再多看看。

#include<iostream.h>
class ca
{
private:
int a1;
public:
ca(int x=0):a1(x){}
virtual void f(){cout<<a1;}
};
class cb:public ca
{
private:
int b1;
public:
cb(int x=0):b1(x){}
void f(){cout<<b1;}
};
int main()
{
ca *p=new ca;
cb *p1=(cb *)p;
p1->f();
return 0;
}

[liuheliaoshi7879]

同意楼上，P没有初始化

[海阔天空的创业与创作]

虚函数测试程序：vc6下调试运行正确

#include<iostream.h>
class ca
{
public:
virtual void f(){ cout << "aaa" << endl; }
};
class cb:public ca
{
public:
virtual void f(){ cout << "bbb" << endl; }
};
void main()
{
ca *pa = new ca();
cb *pb = (cb *)pa;
pa->f();//aaa
pb->f();//aaa

cb *p = new cb();
p->f();//bbb
}