Thread: Appropiate class interface design

What is the preferred way to read values of class members from an other class? For example: If class ClassA contains variables a,b,c, and ClassB contains a method that prints the values of a,b and c, how should an instance of ClassB that declares one instance of ClassA classA_Inst as one of it's members access the values of a, b and c from classA_Inst?

Code:

#include <iostream>

class ClassA
{
public:
    int a,b,c;
}

class ClassB
{
private:
    ClassA classA_Inst;
public:
    void print_abc()
    {
        std::cout << classA_Inst.a << classA_Inst.b << classA_Inst.c << std::endl;
    }
}

.........
ClassB classB_Inst;
classB_Inst.print_abc();

Or

Code:

#include <iostream>

class ClassA
{
private:
    int a,b,c;
public:
    int getA() return a;
    int getB() return b;
    int getC() return c;
}

class ClassB
{
private:
    ClassA classA_Inst;
public:
    void print_abc()
    {
        std::cout << classA_Inst.getA() << classA_Inst.getB() << classA_Inst.getC() << std::endl;
    }
}

.........
ClassB classB_Inst;
classB_Inst.print_abc();

Or

Code:

#include <iostream>

class ClassB;

class ClassA
{
private:
    int a,b,c;
public:
    void getABC(ClassB* classB_ptr)
    {
        classB_ptr->copy_a = a;
        classB_ptr->copy_b = b;
        classB_ptr->copy_c = c;
    }
}

class ClassB
{
private:
    ClassA classA_Inst;
public:
    int copy_a, copy_b, copy_c;
    void print_abc()
    {
        classA_Inst.getABC( this );
        std::cout << copy_a << copy_b << copy_c << std::endl;
    }
}

.........
ClassB classB_Inst;
classB_Inst.print_abc();

Or have I missed something ? There must be some better ways to do that...

Well, all of the three approaches are valid. You can any one of them. But if you consider it from the design perspective. You must look into "Coupling & Cohesion". Your classes have dependency. So it is better to remove this dependency and increase the inter class dependency by putting the print() method in the same class as well.

What is the preferred way to read values of class members from an other class?

Normally this is done, as has been said, via public accessors or public 'getters'.