Subj : Re: Need help, please!
To   : borland.public.cpp.borlandcpp
From : "Ed Mulroy [TeamB]" <dont_email_me@bitbuc.ket>
Date : Tue Nov 25 2003 06:52 pm

Here is one.  I'll be back with another in a few minutes.

-------------------------------------------
C:\Lookat\q421
>type q421.cpp

// partial declaration so the function
// prototype of the operator will know
// something of what the symbol 'ClassA' means

class ClassA;


// Function prototype for the operator
//
// You don't need a friend operator for two
// class arguments because you already have
// that from the member function.  You may need
// one for subtracting the class from an int.
//
// Note that this uses a reference, not an instance
// (call by reference instead of by value)

int operator - (int i1, const ClassA& obj2);


class ClassA
{
private:
    int iMember; // Make class data private
    // If it were public then you would be
    // able to access it so why would you
    // need a friend function?

public:
    // added constructor insures behavior
    // is always deterministic
    ClassA() : iMember(0) {}
    ClassA(int i) : iMember(i) {}

    // added accessor function, gets the value
    int Value() const { return iMember; }

    // added mutator function, changes the value
    void Value(int i) { iMember = i; }

    // note that this uses references, not instances
    ClassA operator - (const ClassA& Obj ) const
    {
        ClassA tmp;
        tmp.iMember = iMember - Obj.iMember;
        return tmp;
    }

    friend int operator - (int i1, const ClassA& obj2);

// the function below is not needed because
// it duplicates what the member function does
//    friend ClassA operator-(const ClassA Obj1, const ClassA Obj2);
};


// because we now have the Value() member function,
// we could get away from needing this to be a friend
// however I'll write it to use iMember to illustrate that
// a friend function works
int operator - (int i1, const ClassA& obj2)
{
    return i1 - obj2.iMember; // could have used obj2.Value()
}

#include <iostream>

using namespace std;

int main()
  {
  ClassA obj1(5);
  ClassA obj2(3);
  ClassA result = obj1 - obj2;

  cout << "obj1.Value() = " << obj1.Value() << endl;
  cout << "obj2.Value() = " << obj2.Value() << endl;
  cout << "obj1.Value() - obj2.Value() = " << result.Value()
       << endl;

  cout << "17-obj2 Using friend: " << 17 - obj2 << endl;
  return 0;
  }

C:\Lookat\q421
>

C:\Lookat\q421
>bcc32 -WCR q421
Borland C++ 5.6.4 for Win32 Copyright (c) 1993, 2002 Borland
Q421.CPP:
Turbo Incremental Link 5.64 Copyright (c) 1997-2002 Borland

C:\Lookat\q421
>q421
obj1.Value() = 5
obj2.Value() = 3
obj1.Value() - obj2.Value() = 2
17-obj2 Using friend: 14

C:\Lookat\q421
>
-------------------------------------------

..  Ed
'
> Bojidar Markov wrote in message
> news:3fc3d0e3@newsgroups.borland.com...

.