Multiple Inheritance and inherited data member in the derived class constructor initialisation list

Question

I have written a simple program that deals with repeated inheritance. I use a base class, two child classes and a grandchild class

class Parent{
public: 
Parent(string Word = "", double A = 1.00, double B = 1.00): sWord(Word), dA(A), dB(B){
}


//Member function
void Operation(){
cout << dA << " + " << dB << " = " << (dA + dB) << endl;
}

protected: 
string sWord;
double dA;
double dB;
};

Now here is the first child class

 class Child1 : public Parent{
 public: 
//Constructor with initialisation list and inherited data values from Parent class   
Child1(string Word, double A, double B , string Text = "" , double C = 0.00, double D = 0.00): Parent(Word, A, B), sText(Text), dC(C), dD(D){};


//member function
void Operation(){
cout << dA << " x " << dB << " x " << dC << " x " << dD << " = " << (dA*dB*dC*dD) << endl;}

void Average(){
cout << "Average: " << ((dA+dB+dC+dD)/4) << endl;}


protected: 
string sText;
double dC;
double dD;
};

Here is the second child class

class Child2 : public Parent {
public: 
//Constructor with explicit inherited initialisation list and inherited data values from Base Class
Child2(string Word, double A, double B, string Name = "", double E = 0.00, double F = 0.00): Parent(Word, A, B), sName(Name), dE(E), dF(F){}


//member functions
void Operation(){
cout << "( " << dA << " x " << dB << " ) - ( " << dE << " / " << dF << " )" << " = "
    << (dA*dB)-(dE/dF) << endl;}

void Average(){
cout << "Average: " << ((dA+dB+dE+dF)/4) << endl;}

protected: 
string sName;
double dE;
double dF;
};

Here is the grandchild class that deals with multiple inheritance

 class GrandChild : public Child1, public Child2{
 public:
 //Constructor with explicitly inherited data members
 GrandChild(string Text, double C, double D,
               string Name, double E, double F): Child1(Text, C, D), Child2(Name, E, F){}


//member function
void Operation(){
cout << "Sum: " << (dC + dD + dE + dF) << endl;
}

};

In the main function I then create a GrandChild object and initialise it like so:

GrandChild gObj("N\A", 24, 7, "N\A", 19, 6);

//calling the void data member function in the GrandChild class
gObj.Operation();

The answer I get to this is

SUM: 0

However the answer should be 56! Clearly the default inherited values used in the constructor for the GrandChild class are being used, and not the data values that are included in the construction of the GrandChild object. How can I solve this problem?

Tell this to your professor, since you don't have any question. — P0W, Sep 01 '14 at 13:15
It is not the default values in the constructor of the grand child object that are used, but the ones in the constructors of the child objects.. You actually gave values to A and B, but not to C D and E, check your parameters orders and default values in your child classes — Drax, Sep 01 '14 at 13:48
When I change the values of C D E and F in the respective child constructors the void Operation() displays a different result accordingly. — A Big Ball Of Lettuce, Sep 01 '14 at 14:02
However What I want is for the data values supplied to the object gObj to be used INSTEAD of these default values. How do I do this? — A Big Ball Of Lettuce, Sep 01 '14 at 14:03

score 2 · Answer 1 · answered Sep 01 '14 at 15:25

In order to get the code to work as I want I made these changes

  //Constructor with explicitly inherited data members
GrandChild(string Word, double A, double B, string Text, double C, double D,
      string Name, double E, double F):
          Child1(Word, A, B, Text, C, D), 
              Child2(Word, A, B, Name, E, F){ }

Basically each Child class inherits its own seperate Parent class. The data member of this Parent class appear in both the child classes constructor lists. When constructing the GrandChild class I declare these values as parameters in its constructor (only once to avoid duplication)! I also include the inherited child classes.

In main I then can create a GrandChild object like so:

GrandChild gObj("n\a", 0.00, 0.00, "text", 3, 3, "text", 3, 3, 7);

And using the dot operator and the void member function I get the correct answer:

gObj.Operation()

which is:

sum: 12

Multiple Inheritance and inherited data member in the derived class constructor initialisation list

1 Answers1