看看你的父类是否是public的，如下是正确的范例：

class Dog:public Animal
{
public:
	Dog(){cout<<"dog constructor"<<endl;}
	virtual ~Dog(){cout<<"dog destructor"<<endl;}
	void cry() const{cout<<"dog cry..."<<endl;}
};

如果：

class Dog:Animal
{
public:
	Dog(){cout<<"dog constructor"<<endl;}
	virtual ~Dog(){cout<<"dog destructor"<<endl;}
	void cry() const{cout<<"dog cry..."<<endl;}
};

这样就会报错。