在基類中，純虛擬函式也不一定不能定義。以前一直認為純虛擬函式只能被派生類定義，看了另一本書以後，才發現也有特殊情況。

class CBase{
public:
 virtual void pure() = 0;
};

class CDerived:public CBase{
public:
 void pure() {cout<<"CDerived::pure"<<endl;}
 void foo(){CBase::pure();}
};
void CBase::pure(){cout<<"CBase::pure"<<endl;}

int main(int argc, char **argv)
{
 CDerived d;
 d.CBase::pure();
 d.foo();
 d.pure();
 CBase *b = &d;
 b->pure();
 return 0;
}