c ++无法将派生类转换为基类

Question

我有一个非常简单的基类/派生类场景:

#include <tchar.h>
#include <stdio.h>
#include <iostream.h>
#include <conio.h>

       class BaseChannel{
          private:
          public:
           virtual ~BaseChannel(){};
           virtual void SayBoo( bool SelectAll)=0;
       };

       class gdbChannel: BaseChannel{
       public:
         void SayBoo(bool SelectAll) {if (SelectAll) cout<<"boo";}
       };

       class UsesChannel{
       public:
          BaseChannel * c;
       };


int _tmain(int argc, _TCHAR* argv[])
{
   gdbChannel gc;
   UsesChannel uc;
   // uc.c = &gc; //cannot convert gdbChannel* to BaseChannel*
   uc.c = (BaseChannel*)&gc; // works
   uc.c->SayBoo(true);
   getch();
    return 0;
}

我上面说明的初始实现将无法编译.有谁能解释为什么？我觉得因为gdbChannel明确是BaseChannel的一个实例,所以不需要强制转换.

Answer 1

那是因为gdbChannel不使用public继承来派生BaseChannel(class类型的默认值是private).

如果公共继承是你想表达的,那就写下:

class gdbChannel : public BaseChannel{
//                 ^^^^^^
public:
    void SayBoo(bool SelectAll) {if (SelectAll) cout<<"boo";}
};