overriding virtual function differs from 'Base::afn' only by return type or calling conven

#include
using namespace std;
//-------------------
class Base
{
public:
virtual Base* afn(){cout<<"in base class\n";return this;}
};
class Sub:public Base
{
public:
virtual Sub* afn(){cout<<"in sub class\n";return this;}
};
void test(Base& s)
{
Base* p;
p=s.afn();
}
int main()
{
test(Base());
test(Sub());
}

virtual SubClass* afn()

这个你要是把afn函数里面+个参数还可以实现一下函数的的重载

如果是你这样不能实现函数的重载,因为重载函数不以返回值来区分.

把virtual SubClass* afn() 改为:

virtual Base * afn()或者Base * afn()都可以

建议你去看一下虚函数的作用;

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