Hi Freedo:

I think maybe I misunderstand the concept
of pure virtual function and abstract class when some classed inherit
from it. What I understand is: If a new class(concrete class, not abstract one)
inherits from an abstract class, it must define all of the pure virtual
functions, if not, then this new class has an error and we can justify this
error not until we define an object of this new class.

And what I can get the view of c++ compiler is : if a new class inherits
from an abstract class, new class doesn't need to define all of the pure
virtual functions, that's no problem, but you can't define an object of this
new class, if you define one, you are wrong.
Is that right?




example:



class Pet
{
public:
virtual void speak() const = 0;
virtual void eat() const = 0;
};

class Dog : public Pet {
public:
void eat() const {}
};



// if you write here, and then press F7, no error.



int main()

{

//! Dog d; that's an error.

}



// why compiler must wait to tell me errors until I've created an object.

// I think if I create the class dog and then compile it, the compiler should tell me the error, 'cos I don't override all of the pure virtual functions.



如果我说的不清楚可以用汉语交流一下, 我已经尝试在Microsoft的newsgroup里面讨论这个问题,基本上大家对我对于Compiler的看法表示漠视. Freedo我想听听你的意见。



因为我想如果继续从Dog继承下去，到Dog100(有点儿夸张)的时候(说明一下:从Dog1开始我会全部override Pet中的Pure virtual functions,虽然对于函数speak来讲我觉得应该叫做redefine而不是override了，因为Dog类里面没有实现)，我去实现一个Dog100的对象，那么编译器告诉我没有实现Pet这个Abstract class的speak纯虚函数,那么我们是不是要花时间去寻找到底我们继承中哪个类出了问题呢? 虽然很快可以找到但是我仍然认为是很花时间的.



另外我认为继承到Dog这个类的时候，Dog类几乎已经没有任何用处:

1.如果我们利用它创建对象，肯定有编译问题。

2.如果我们让它作为Base class继续去inherit, 那么我觉得是会有更大的 potential error 在其中的。



Freedo，感谢你花时间看我的问题，我尝试过去Up9rade.com去贴这个问题，但是三次都没有成功，再次感谢。

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