Composition,private Class member variables and methods

**sigur47** · 01-29-2012

I have a class A which has a class B as a private member variable.Class b also has a class C as a private member variable.(A->B->C).. I am trying to call a method which has an implementation in class C but i keep getting an erroR saying the object of class C which i declared in class B is private when i try to write a method in class A. e.g B->C->setGreeting();

class Country
{
public:
void setPoints(int x,int y);
private: City * city;
}
// i am having problems here with error Point * city p is private
void Country::setPoints(int x,int y){
city->p->setPoints(x,y);

}
class City
{
public:
City();
virtual ~City();
protected:
private:

Point *p;
};

class Point
{
public:
Point();
virtual ~Point();
void setPoints(int x,int y);

protected:
private:
int x;
int y;
};
void Point::setPoints(int xp,int yp){
x=xp;
y=yp;
}

**laserlight** · 01-29-2012

It seems that the setGreeting member function of class C was not declared public.

**sigur47** · 01-29-2012

Originally Posted by laserlight

It seems that the setGreeting member function of class C was not declared public.

It is declared public

**laserlight** · 01-29-2012

Sigh. Of course. You are trying to access a private member of B from A, right?

Just post the code. I hate misreading your prose. Code poetry is better.

**sigur47** · 01-29-2012

Originally Posted by laserlight

Sigh. Of course. You are trying to access a private member of B from A, right?

Just post the code. I hate misreading your prose. Code poetry is better.

yup That's what i am trying to do.I have just included a private method in class B to be able to access the private member variable c.The code is quite sensitive that's why i do not want to post it

**laserlight** · 01-29-2012

Originally Posted by sigur47

I have just included a private method in class B to be able to access the private member variable c.

That won't work: A cannot access the private members of B, whether they are member variables or member functions.

Originally Posted by sigur47

The code is quite sensitive that's why i do not want to post it

Then come up with the smallest and simplest program that demonstrates the error.

**sigur47** · 01-29-2012

Originally Posted by laserlight

That won't work: A cannot access the private members of B, whether they are member variables or member functions.

Then come up with the smallest and simplest program that demonstrates the error.

Would do so now thanks for your patience

**sigur47** · 01-29-2012

Originally Posted by laserlight

That won't work: A cannot access the private members of B, whether they are member variables or member functions.

Then come up with the smallest and simplest program that demonstrates the error.

i have posted a code up please kindly have a look at it

**Elysia** · 01-29-2012

Use code tags, please.
Also, the compiler is right to complain:
Country is not supposed to know how a City is implemented. You should provide public methods in City to allow the addition Points, whatever they are.

**sigur47** · 01-29-2012

Originally Posted by Elysia

Use code tags, please.
Also, the compiler is right to complain:
Country is not supposed to know how a City is implemented. You should provide public methods in City to allow the addition Points, whatever they are.

I cannot add extra public method to my player object because its implementing an interface

**Elysia** · 01-29-2012

Just because it is implementing an interface does not mean you cannot add more functions. Of course, the question is, does it make sense? This may or may not be.
Regardless, the design you have now is bad, and cannot work. So either you add more functions to the class, augment the interface or make a new interface and implement it.

**sigur47** · 01-29-2012

Originally Posted by Elysia

Just because it is implementing an interface does not mean you cannot add more functions. Of course, the question is, does it make sense? This may or may not be.
Regardless, the design you have now is bad, and cannot work. So either you add more functions to the class, augment the interface or make a new interface and implement it.

the interface cannot be changed because everyone working on the project has to have the same interface.i cant use private methods because it wont work.Would there be another way of designing my program

**Elysia** · 01-29-2012

OK, so there are two ways:
- Make the variable public (which is a dumb way).
- Make a public method that does what you want (which is a good way).

You can implement the public method in several ways, obviously. It can be inherited from one or more interfaces, or it can be a method only existing in that specific class.

**laserlight** · 01-29-2012

Originally Posted by sigur47

the interface cannot be changed because everyone working on the project has to have the same interface.

Go back to your team and report that there is something deficient about the interface of B. Discuss and change the interface to add the functionality needed to access/modify C from A through B.

Of course, if by implementing an interface to mean to say that you're responsible for designing and implementing C, but C must implement an interface specified by say, an abstract base class that has been agreed on to serve as a pure interface, then that is a different matter: you can freely add to the public interface of C as long as you are also implementing the interface specified.

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