Question

In c++ I have an Abstract class A:

 class A
 {
 public:
    A(){}
    virtual ~A(){}
    virtual void out(std::ofstream& outFile) = 0;
    virtual void in(std::ifstream& inFile) = 0;
};    

And B class in which I want to use virtual methods:

class B : public A
{
public:
   B();              
   double angle;
   int index;


   virtual void out(std::ofstream& outFile);
   virtual void in(std::ifstream& inFile);

};

Now here is a question: I want to use B class variable like (int index) in virtual methods:

virtual void out(std::ofstrea& outFile)
{
    outFile<< index << angle;       
}

Here I get compiler error that angle and index are not declared in this scope. It is somewhat logical because this variables are not declared in class A.
Now how can I get access to variable angle and index in virtual methods?

Thanks for your help.

Answer 1

If you’re implementing the method outside the class, you don’t mark it as virtual and you qualify its name:

void B::out(std::ofstrea& outFile)
{
    outFile<< index << angle;       
}