virtual template function is in working c++ ????

Question

hi All  after so much surfing and cominng across various opinions I just want to know a clear idea about the following problem.

I've a base class with template and a dervied class of course with a template.Then can some of the functions declared virtual in base class and reimplemented in derived class work in c++ ..??

ex:

template<class Type>

class Hello{

public:

    virtual Type foo(Type jk){

        cout<<"jk is in Base class "<<jk<<endl;

        return jk;

    }

};

template<class Type>

class HelloD:public Hello<Type>{

    public:

     Type foo(Type jk){

        cout<<"jk is in derived class "<<jk<<endl;

        return jk;

    }

};

 But I see  the above code works with Qt compiler.Which one the pure virtual or both  abstract and  virtual base class template are not allowed in c++ .

regards

simbu 

Answer 1

What exactly do you expect your code to do, and how does the actual behavior differ?
 

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David Wilkinson | Visual C++ MVP

Answer 2

okk..I want to create a template base class A and a template dervied class B , derived from A..I simply want to have some member functions of A as virtual functions using template parameter and I  want to reimplement them in class B  differently .Example is as shown in my first post.I'm asking is this legitimate  to do in c++..??

If no why and if yes then will it be same with pure virtual functions..??

regards

simbu

Answer 3

You haven't shown how you use these classes, or said what you expect to happen.

But the answer to your underlying question is: Yes, functions in a template class can be virtual.

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David Wilkinson | Visual C++ MVP

Answer 4

A simple concept we use template to implement generic function and classes . But default behaviour of classes and function always persist and it doesn't matter how you are implementing your class .

Thanks

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Rupesh Shukla

Answer 5

Hi simbu,

I have tried the codes you posted in VS2010 SP1 on my side. And in main function of a Win32 Console application, I added codes in main function as follows:

	Hello<int>* hello=new Hello<int>();
	HelloD<int>* hellod=new HelloD<int>();
	int a=hello->foo(3);
	int b=hellod->foo(5);

After running the application, I saw the following result of Console Window:

So we know that we can program like this in C++. If we declare a pure virtual function in Base class like this:

public:  virtual Type foo(Type jk)=0;

Then the Base class can not be initialized, we can still get result 5 from derieved class with the codes above.

I hope this reply is helpful to you. If you have any questions, please feel free to let me know.
Have a nice day!

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Helen Zhao [MSFT]
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