Overriding a protected variable in a dervied class

Question

I have the following project, in which I define a main class called frame, and from that class I derive multiple type of classes. The main class "frame" has a protected variable defined as:

class frame {
protected:
    char header[4];
}

And in the derived classes I want the array header to have different size, as the following:

class dervied_frame : public frame {
protected:
    char header[8];
}

So my question is it possible to override the protected variable in the derived classes? and how to do that?

Note: I don't want to define the header as a pointer and in then in the constructor I define the size that I want through dynamic allocation.

its simple, dont use protected variables (most of the time there's a better ideia to your implementation) — , May 01 '14 at 17:09
No, because the "header" has a fixed size. You can easily do this with dynamic allocation. Why is that not a valid option? — IdeaHat, May 01 '14 at 17:09
@HA-AS dynamic allocation or what IronMensan mentioned, but read this http://stackoverflow.com/a/3933120/2709465 — , May 01 '14 at 17:18
well the simplest would be to use `std:vector` instead of char[]. — AndersK, May 01 '14 at 17:19

score 3 · Accepted Answer · answered May 01 '14 at 17:13

You could use a template like this:

template <int headerSize>
class frame {
protected:
    char header[headerSize];
};

class dervied_frame : public frame<8> {
};

But then every sub-class will have a unique base class so you won't really be able to do anything with a frame *. Depending on what you are using this class for, that restriction could be a deal breaker. You can partially get around this by adding another super-class:

class frame {
public:
    void otherMethodsHere();
};

template <int headerSize>
class frameHeader : public frame {
protected:
    char header[headerSize];
};

class dervied_frame : public frameHeader<8> {
};

@HA-AS The caveat for the templated base class is an important one. — Captain Giraffe, May 01 '14 at 18:20

Overriding a protected variable in a dervied class

1 Answers1