c++中虚函数的默认值

class cbase
{
public:

    virtual void func(int a = 10)
    {
        cout << "this is cbase func:" << a << endl;
    }
};

class csub : public cbase
{
public:
    void func(int a = 20)
    {
        cout << "this is csub  func:" << a << endl;
    }
};

  cbase * cbToCb = new cbase;
　cbase * cbTocSub = new csub;
　csub  * cSubTocSub = new csub;

　　cbToCb->func(); // "this is csub func:10"
　　cbTocSub->func(); // "this is csub func:10"
　　cSubTocSub->func(); // "this is csub func:20"