question abot classes

**baxy** · 09-02-2013

Hi,

i am starting to play around classes and oop and i have a very basic question that i cannot grasp. so the situation is:

I have a class X and several functions operating on it (are a part of that class). Now, as far as i understood, i can pass a function to a class by saying X::func() but now this function is a part of my class X and if i need to pass it down to another class i need to make this other class a part of my X class, is that right ? If yes then how would one share a function between two or more different unrelated classes ?

thnx

baxy

PS.

did i completely misunderstand the whole thing ??

**manasij7479** · 09-02-2013

You are confused about the difference between 'has a' and 'is a' relationships between classes.
For example, you have a class called Animal and another called Human.
A human is an animal.
So, you derive human from animal and implement/override necessary member functions.
This is called inheritance.

You can also have composition, in which a object of type..say..Brain may literraly be a member of a human object.

You can have 'nested' classes, which for which I can not find a good analogy here....
(Humans do not have iterators

)

**baxy** · 09-02-2013

ok so if i have a method that formats some private data structures , let say a simple array . and i want to use the same function on a compleatly unrelated class to do the same thing on a private array in that class how would i do this. the rreason why i am aking this question is because to me oop right now looks so un-flexible in comparison to simple procedural design (nicer and more efficient but extreamly un-flxible ). so is something like that possible and how would i do it? example:

Code:

 
class X{
      Constr(int i=0 )throw( ...bla...);
      ~Constr()throw(...bla...);

     private:  
     int *array; 
      

};



class Y{
      Constr(int i=0 )throw( ...bla...);
     ~Constr()throw(...bla...);

private: 
      int *array;
      

};

modif(){
  // it modifies arrays
}

how would i make the function modif work on both arrays in classes X and Y ?

**c99tutorial** · 09-02-2013

Originally Posted by baxy

ok so if i have a method that formats some private data structures , let say a simple array . and i want to use the same function on a compleatly unrelated class to do the same thing on a private array in that class how would i do this.

It sounds like what you want is a superclass. Then you can put the similar function into the superclass or if it changes based on the subclasses, let them each have their own version. Going on your example here is one that should give some ideas

Code:

class Sup {
protected:
    static const int lim_ = 10;
    int array_[lim_];
public:
    virtual void modif() = 0;
    void fill(int i) {
        for (int j=0; j < lim_; j++) {
            array_[j] = i;
        }
    }
    
    friend std::ostream & ::print(std::ostream &, const Sup &);
};

std::ostream &print(std::ostream &os, const Sup &s)
{
    using std::cout;
    cout << s.array_[0];
    for (int i = 1; i < s.lim_; i++) {
        cout << " " << s.array_[i];
    }
    return os;
}
        
class X : public Sup {
private:
    const int modifchar_ = 42;
public:
    X(int i=0) {
        fill(i);
    }
    ~X() { }

    virtual void modif() {
        for (int i=0; i < lim_; i++) {
            array_[i] = modifchar_;
        }
    }
};

class Y : public Sup {
private:
    const int modifchar_ = 97;
public:
    Y(int i=0) {
        fill(i);
    }
    ~Y() { }

    virtual void modif() {
        for (int i=0; i < lim_; i++) {
            array_[i] = modifchar_;
        }
    }
};

Demonstration using the classes

Code:

int main()

{

    X x;
    Y y;
    x.fill(10);
    y.fill(20);
    print(cout, x) << endl;
    print(cout, y) << endl;
    x.modif();
    y.modif();
    print(cout, x) << endl;
    print(cout, y) << endl;    
    return 0;

}

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