Question

So i have a interface class

class interfaceClass
{
 public:   
    virtual void func1( void ) = 0;
    virtual void func2( void ) = 0;

protected:
    int m_interfaceVar;
}

and a class that inherits from it.
Why can’t i set the member variable of the interface class as follows.

class inhertitedClass : public interfaceClass
{
   inheritedClass(int getInt): m_interfaceVar(getInt){};
   ~inheritedClass(){};
}

and i have to do it like this

class inhertitedClass : public interfaceClass
{
   inheritedClass(int getInt){ m_interfaceVar = getInt;}
   ~inheritedClass(){};
}

I’m sorry if this is a dumb question, but i just ran in to it the other night while i was switching my abstract class into an interface class (the back to an abstract class).

Answer 1

The initializer list in a constructor can specify the ctor for the base classes first and foremost. By depriving interfaceClass of a (protected) constructor (which it obviously should have) you’ve cut off that lifeline.

So add that protected ctor, e.g.:

class interfaceClass
{
 public:   
    virtual void func1( void ) = 0;
    virtual void func2( void ) = 0;

protected:
    int m_interfaceVar;
    interfaceClass(int x) { m_interfaceVar=x; }
}

and then you can do things the right way, namely

class inhertitedClass : public interfaceClass
{
   inheritedClass(int getInt): interfaceClass(getInt){};
   ~inheritedClass(){};
}