CODEWITHSUNDEEP
c++operator-overloading
darko
darko

Reputation: 2458

Operator overloading with friend function error

I am working on an assignment that introduces me to operator overloading. I have to overload some binary operators as member functions and also as friend functions. My member function that overloads the "+" operator works fine but my friend function that overloads the "-" operator seems to have trouble finding data that the member function is able to use.

class def:

class matrix
{
    friend ostream& operator << (ostream&, const matrix&);
    friend bool operator == (const matrix &, const matrix &);
    friend matrix operator - (const matrix &, const matrix &);

private:
    int size;
    int range;
    int array[10][10];

public:
    matrix(int);
    matrix(int, int);
    bool operator != (const matrix &) const;
    matrix operator + (const matrix &) const;
    const matrix & operator = (const matrix &);
};

"+" overload:

matrix matrix::operator + (const matrix & a) const
{
    matrix temp(size,range);

    for (int i = 0; i < a.size; i++)
        for (int j = 0; j < a.size; j++)
            temp.array[i][j] = a.array[i][j] + array[i][j];

    return temp;
}

"-" overload:

matrix operator - (const matrix & a, const matrix & b)
{
    matrix temp(size, range);

    for (int i = 0; i < a.size; i++)
        for (int j = 0; j < a.size; j++)
            temp.array[i][j] = a.array[i][j] - array[i][j];

    return temp;
}

The error I am getting in the friend function is that size, range, and array are all undeclared. I am confused because I thought member and friend functions both had equal access to data in a class and I basically doing the same thing in both functions. Does anyone know what my issue may be?

Upvotes: 0

Views: 1635

Answers (2)

Marius Bancila
Marius Bancila

Reputation: 16338

The friend operator is not part of the class. Thus, it does not know size and range and array. You must use the objects a and b. It should be something like this:

matrix operator - (const matrix & a, const matrix & b)
{
   if(a.size != b.size)
      throw std::exception(...);

   matrix temp(a.size, a.range);

   for (int i = 0; i < a.size; i++)
                for (int j = 0; j < a.size; j++)
                     temp.array[i][j] = a.array[i][j] - b.array[i][j];

    return temp;
}

Upvotes: 5

Shamim Hafiz - MSFT
Shamim Hafiz - MSFT

Reputation: 22124

Though your friend function would be able to access the private data of the Objects, but this doesn't imply that the attributes are in the scope of that function. I mean, it wont act like a member function as you are expecting it to. You would need to provide the size from one of the objects that you are passing.

Upvotes: 0

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