有关C++继承与友元、继承与类型转换详解

#include  

using namespace std; 

class a{
friend class pal;
private:
	int i;
protected:
	int j;
public:
	int k;
};

class b:public a{
protected:
	int l;
};

class c:protected a{};
class d:private a{};
class e:public b{};

class pal{
public:
	void f(a a1){
		cout<

#include  

using namespace std; 

class a{};
class b:public a{};
class c:protected a{};
class d:private a{};
class bb:public b{};
class cc:public c{};
class dd:public d{};




int main() 
{	
	a a1;b b1;c c1;d d1;bb bb1;cc cc1;dd dd1;
	a* a1=&b1;//ok
	a* a2=&c1;//error
	a* a3=&d1;//error
	a* a4=&bb1;//ok
	a* a5=&cc1;//error
	a* a6=&dd1;//error
	system("pause");
	return 0; 
}