Matrix class operator overloading

[Sp1ke]

Hi Guys,

I'm trying to learn about classes and operator overloading. I took this code (also from this forum as a basis and changed some stuff around:
http://www.cplusplus.com/forum/general/87651/

My Problem is, that the copy assignment operator somehow does not work properly and I can't pinpoint the mistake. The result after performing the operation Matrix A = Matrix B ist still Matrix A.

I would be very grateful for any tip.

Here's the class file:

#include "matrix.h"
#include <iostream>
//#include <stdio.h>
//#include <stdlib.h>
//#include <new>

using namespace std;


//matrix initialisation
matrix::matrix(int r, int c){           //defines the constructor to create a new matrix (dimension r*c) with 0 values
	row = r;
	col = c;
	array = new int*[row];              //initialize empty rows

	for (int i=0; i<row; i++){
		array[i] = new int[col];        //initialize empty columns
		}

	for (int i=0; i<row; i++){
		for (int j=0; j<col; j++){
			array[i][j] = 0;            //fills empty matrix with 0 vales
		}
	}
};

//initialises copy constructor
matrix::matrix(const matrix& m){ //defines the copying constructor
	row = m.row;
	col = m.col;
	array = new int*[row];
	for (int i=0; i<row; i++){
		array[i] = new int[col];
		}
	for (int i=0; i<row; i++){
		for (int j=0; j<col; j++){
			array[i][j] = m.array[i][j];
		}
	}
}

//destructor
matrix::~matrix(){ //destroy matrix
	for (int i=0; i<row; i++){
		delete[] array[i]; //delete columns
		}
	delete[] array; //delete rows
	};




void matrix::setValue(int r, int c, int e){
	array[r][c] = e;
};

int matrix::getValue(int r, int c){
	return array[r][c];
}





//overload operator= (copy assignment operator) - does not create new matrix
matrix matrix::operator=(const matrix& m){

    matrix new_mat(row,col);
	for (int i=0; i<row; i++){
		for (int j=0; j<col; j++){
              new_mat.array[i][j] = m.array[i][j];
            }
        }
        return new_mat;
     }

// overload + operator
matrix matrix::operator+(const matrix& m){
	//  if matrices do not have the same size, return original matrix
	if (row != m.row || col != m.col){
		cerr << "Matrix sizes do not match.";
		return (*this);
	}
	matrix new_mat(row,col);
	for (int i=0; i<row; i++){
		for (int j=0; j<col; j++){
			new_mat.array[i][j] = array[i][j] + m.array[i][j];
		}
	}
	return new_mat;
}

// overload * operator
matrix matrix::operator*(const matrix& m){

	matrix new_mat(row,col);
	for (int i=0; i<row; i++){  //i = rows
		for (int j=0; j<col; j++){  //j = cols
		for(int k = 0; k < col; ++k)
            {
                new_mat.array[i][j] += array[i][k] * m.array[k][j];
            }
		}
	}
	return new_mat;
}

Header:

#ifndef MATRIX_H
#define MATRIX_H


class matrix
{
	int row;
	int col;
	int **array;

	public:
		matrix(int,int); //constuctor
		matrix(const matrix&); //constructor to copy a matrix
		~matrix(); //destructor

        //operator overloads
		matrix operator=(const matrix&);
		matrix operator+(const matrix&);
		matrix operator*(const matrix&);


        void setValue(int r, int c, int e);
		int getValue(int r, int c);
};

#endif // MATRIX_H 

And Main.cpp

#include <iostream>
#include <matrix.h>
#include <cmath>



using namespace std;

int main()
{
	int r = 4;
	int c = 4;
	matrix matrixA(r,c);
	matrix matrixB(r,c);
	matrix matrixC(r,c);

	for (int i=0; i<r; i++){
		for (int j=0; j<c; j++){
			matrixA.setValue(i,j,1);
			matrixB.setValue(i,j,2);
			//matrixC.setValue(i,j,5);
		}
	}

	cout << "matrixA" << endl;
	for (int i=0; i<r; i++){
		for (int j=0; j<c; j++){
			cout << matrixA.getValue(i,j) << "\t";
		}
		cout << endl;
	}
	cout << endl;

	cout << "matrixB" << endl;
	for (int i=0; i<r; i++){
		for (int j=0; j<c; j++){
			cout << matrixB.getValue(i,j) << "\t";
		}
		cout << endl;
	}
	cout << endl;

	cout << "matrixC before addition" << endl;
	for (int i=0; i<r; i++){
		for (int j=0; j<c; j++){
			cout << matrixC.getValue(i,j) << "\t";
		}
		cout << endl;
	}
	cout << endl;

	matrixC = matrixA; // + matrixB;

	cout << "matrixC after addition" << endl;
	for (int i=0; i<r; i++){
		for (int j=0; j<c; j++){
			cout << matrixC.getValue(i,j) << "\t";
		}
		cout << endl;
	}
	cout << endl;
}

[Peter87]

The copy assignment operator should modify the object that you called it on (i.e. *this) and return a reference to the same object.

[Sp1ke]

Great, problem solved!!
Thanks so much!!