Overload cout operator for a dynamic array in a class

Question

I am trying to overload the operator << for cout for a dynamic array in a class. My class and member functions are as follows:

class Matrix{
private:
    int rows;
    int columns;
    double* matrix;
public:
    Matrix();
    explicit Matrix(int N);
    Matrix(int M, int N);
    void setValue(int M, int N, double value);
    double getValue(int M, int N);
    bool isValid() const;
    int getRows();
    int getColumns();
    ~Matrix();
    friend ostream& operator<<(ostream &out, const Matrix&matrix1);

};

    Matrix::Matrix(){
    matrix = NULL;
}

Matrix::Matrix(int N){
    matrix = new double[N * N];
    rows = N;
    columns = N;

    for(int i = 0; i < N; i++){
        for(int j = 0; j < N; j++){
            if(i==j)
                matrix[i * N + j] = 1;
            else
                matrix[i * N + j] = 0;
        }
    }
}

Matrix::Matrix(int M, int N){
    matrix = new double[M * N];
    rows = M;
    columns = N;

    for(int i = 0; i < M; i++){
        for(int j = 0; j < N; j++)
            matrix[i * N + j] =  0;
    }
}

Matrix::~Matrix(){
    delete [] matrix;
}

void Matrix::setValue(int M, int N, double value){
    matrix[M * columns + N] = value;
}

double Matrix::getValue(int M, int N){
    return matrix[M * columns + N];
}

bool Matrix::isValid() const{
    if(matrix==NULL)
        return false;
    else
        return true;
}

int Matrix::getRows(){
    return rows;
}

int Matrix::getColumns(){
    return columns;
}

I've tried to implement the << operator as follows:

ostream& operator<<(ostream &out, const Matrix&matrix1){
Matrix mat1;
int C = mat1.getColumns();
int R = mat1.getRows();

for(int i = 0; i < R; i++){
    for(int j = 0; j < C; j++)
        out << mat1.getValue(i,j) << "\t";
    out << endl;
}
return out;

}

and call it from a function:

void test(){
Matrix mat1(3,4);
cout << mat1 << endl;

}

but this doesn't print anything at all. It seems like the overload functions doesn't get any values for C and R, but I might be wrong. Anyone got some ideas?

It is suppose to print dynamic matrices on the form

a11     a12     a13    . . .
a21     a22     a23    . . .
.        .       .     . . .
.        .       .     . . .
.        .       .     . . .

"It seems like the overload functions doesnt get any values for C and R, but I might be wrong" - Did you set a breakpoint and check the values of C and R? — Qaz
– Qaz, Commented Mar 12, 2013 at 21:37
You're still creating unnecessary local variables, just like you were doing with the constructors earlier. — molbdnilo
– molbdnilo, Commented Mar 12, 2013 at 21:41

masoud · Accepted Answer · 2013-03-12 21:37:52Z

2

You are printing an empty mat1, not given matrix1.

ostream& operator<<(ostream &out, const Matrix& matrix1)
{
    //Matrix mat1;   // <- Comment ythis
    int C = matrix1.getColumns(); // <<- matrix1
    int R = matrix1.getRows(); // <<- matrix1

    for (int i = 0; i < R; i++)
    {
        for (int j = 0; j < C; j++)
            out << matrix1.getValue(i, j) << "\t"; // <<- matrix1
        out << endl;
    }
    return out;
}

answered Mar 12, 2013 at 21:37

masoud

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Comments

juanchopanza · Accepted Answer · 2013-03-12 21:37:32Z

2

You need to print the contents of matrix1. You are creating a local empty matrix mat1 and printing its contents instead.

ostream& operator<<(ostream &out, const Matrix& matrix1) 
{
  int C = matrix1.getColumns();
  int R = matrix1.getRows();

  for(int i = 0; i < R; i++){
    for(int j = 0; j < C; j++)
        out << matrix1.getValue(i,j) << "\t";
    out << endl;
  }
  return out;

}

answered Mar 12, 2013 at 21:37

juanchopanza

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Comments

Sarien · Accepted Answer · 2013-03-12 21:38:05Z

2

Am I seeing this right, Matrix1 is the parameter to operator<< but you are creating a new mat1 and outputting that?

answered Mar 12, 2013 at 21:38

Sarien

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