Virtual Keyword

I have doubt using the keyword "virtual". In C++ if I create a pure virtual function then the derived class has to implement it. If the derived class does not declare the pure virtual function with the keyword "virtual" the MVC++ does not warn me about it. But if I had the keyword virtual in the derived class it still doesn't make any difference.

Here is a sample code:

Code:

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class A 
{
public:
        A();
        virtual ~A();
        virtual void A::op() = 0;
 
};
 

class B : public A 
{
public:
        B();
        virtual ~B();
        void op(); // doesnt make any difference if I have virtual or don't have it.
 
};

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I want to know if there is any difference using / not using the virtual keyword?

Quote:

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If the derived class does not declare the pure virtual function with the keyword "virtual" the MVC++ does not warn me about it. But if I had the keyword virtual in the derived class it still doesn't make any difference.

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The virtual function inherited is still virtual either way.

>I have doubt using the keyword "virtual".
You have a question. A doubt is different.

>If the derived class does not declare the pure virtual function
>with the keyword "virtual" the MVC++ does not warn me about it.
No compiler will warn you about it. It's perfectly legal to omit the virtual keyword in the derived class, and the member function will still be virtual.

Thanks for your response, is it used just for better understanding of the code?
SO IT MAKES NO DIFFERENCE AT ALL IF I USE IT/ NOT RIGHT??

[Mis]quoted from a book, if a function is going to be virtual, or you want it to be virtual, just type it and get it over with. You'll remember that way.

>> SO IT MAKES NO DIFFERENCE AT ALL IF I USE IT/ NOT RIGHT??

It makes no difference to the compiler if you don't put it in the derived class, but it does make a difference to people reading your code. Making your code clear and self-explanatory is worth putting a little bit of effort into.

Quote:

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If the derived class does not declare the pure virtual function with the keyword "virtual" the MVC++ does not warn me about it.

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This is because the compiler assumes that the inherited class will also be an interface (pure virtual class); thus. it doesn't warn you. However, if you tried creating an instance of the inherited class, you would get a compiler warning telling you it's impossible to make an instance of the class.