Win32/C++ Class Inheritance problem

I am writing an GL effect system in my application so i hav开发者_StackOverflowe a superclass called

cEffect - which handles loading/parsing configuration file for each effect

and other inherited classess

cFX<name> - for every effect i add ( blur, bloom, chaos,... ).

The code is simplified here but looks like this:

Class cEffect
{
    public:
     bool ParseString(...);

    private:
     int m_nStartFrame;
     int m_nEndFrame;
     float m_fSpeed;
};


// Blur effect
Class cFXBlur : public cEffect
{
  public: 
   bool RenderFrame(...);
};
// Bloom effect
Class cFXBloom : public cEffect
{
  public: 
   bool RenderFrame(...);
};
// Scene drawing effect
Class cFXScene : public cEffect
{
  public: 
   bool RenderFrame(...);
};
// Clear the depth/color buffer
Class cFXClearBuffers : public cEffect
{
  public
   bool RenderFrame(...);
}

Now, the demo engine handles a

std::vector<cEffect *> m_pvEffects;

Vector that has a list of effects added. And when an effect is added to the current time (let's say i add a blur) i add it like:

// Blur to be added 

cEffect *newEffect = new cFXBlur;
newEffect->SetStartTime(x);
newEffect->SetEndTime(y);
newEffect->SetPower(13.0f);
newEffect->SetTexture(...);

// Now add the effect to the effects list.
m_pvEffects.push_back(newEffect);

Now, when i render i iterate through m_pvEffects list - but also i would like to call an RenderFrame method ( which is public in every CFX<name> effect).

(*it)->RenderFrame(...) 

But compiler says:

error C2039: 'RenderFrame' : is not a member of 'CEffect'

I kinda understand why it happens but can't really think of a way how can i fix this, can you guys help me out please - it seems like i lost the plot ...

Thanks for any suggestion, what can i do to add CFX to a cEffect vector and later use -> RenderFrame method?

You should change your class cEffect to:

Class cEffect
{
    public:
     bool ParseString(...);
     virtual bool RenderFrame(...) = 0;

    private:
     int m_nStartFrame;
     int m_nEndFrame;
     float m_fSpeed;
};

You need the keyword virtual, if you want to redefine a method in a subclass. The = 0 makes the class cEffect abstract (i.e. you cannot create an object directly of the type cEffect), therefore subclasses must implement the method RenderFrame(...)

The error occurs, because cEffect has no member function called RenderFrame. What you want is a virtual function, a fundamental concept of object oriented programming. Basically you need to add a function

virtual bool RenderFrame(...);

to your cEffect definition. The virtual keyword basically tells the compiler to resolve it at runtime. This means if you call this method on a cEffect pointer or a reference, the corresponding method of the concrete derived class this pointer or reference point to is called. In this case you should also declare the method as virtual in all derived classes (although this is not neccessary, it makes your code clearer).

If you do not want the base class method to do anything and you want to require all derived classes to override it with their own implementation, then you can make this method pure virtual in the base class, by decralring it like

virtual bool RenderFrame(...) = 0;

This basically tells the compiler, that this is an abstract method, which doesn't have a concrete implementation and is only implemented by derived classes.

This is a very simplified explanation (appologies to every expert who thinks my wordings not 100% exact). You should read some more material on object oriented programming, especially in conjunction with C++.