Question

I have a matrix:

#ifndef MATRIX_H
#define MATRIX_H

class Matrix
{   
    public:
        Matrix(int rows, int columns);
        Matrix(int, int, int** matrix); 
        Matrix(Matrix* copy);
        ~Matrix();

        void Set(int, int, int);
        void SetMatrix(int, int, int** matrix);             
        void Print();
        void ZeroMatrix(int,int,int** matrix);      
        void Add(Matrix* B);
        void Subtract(Matrix* B);
        void Copy(Matrix* B);

        int** Multiply(Matrix* B);
        int** Create(int,int);
        int** Get();
        int** Transpose();
        int** Scalar(int);

        int Get(int,int);
        int Rows();
        int Columns();

        Matrix operator*(int);

    private:
        int** _matrix;
        int _rows;
        int _columns;
};

#endif

Here’s the implementation:

Matrix Matrix::operator*(int scale)
{
    return Matrix(_rows, _columns, Scalar(scale));
}

And for a school assignment we have to overload the multiple operator to work with integer scalar. The problem is I keep getting this error:

main.cpp: In function ‘int main(int, char*)’:
main.cpp:18:15: error: no match for ‘operator’ in ‘4 * B’

Breaking code:

#include "Matrix.h"
#include <fstream>
#include <iostream>

int main(int argc, char *argv[])
{   
    Matrix* A = new Matrix(4,2);

    A->Set(0,0,1);  
    A->Set(0,1,2);
    A->Set(1,0,3);
    A->Set(1,1,4);  
    A->Print();

    Matrix B(A);
    B.Print();

    Matrix C(4 * B); //this line
    C.Print();


    delete A;

    return 0;
}

Any ideas?

edit # 1:

the code:

Matrix operator*(int); 
        Matrix operator* (int, const Matrix &);

generates:

In file included from main.cpp:1:0:
Matrix.h:31:40: error: ‘Matrix Matrix::operator*(int, const Matrix&)’ must take either zero or one argument
In file included from matrix.cpp:1:0:
Matrix.h:31:40: error: ‘Matrix Matrix::operator*(int, const Matrix&)’ must take either zero or one argument
matrix.cpp:207:50: error: ‘Matrix Matrix::operator*(int, const Matrix&)’ must take either zero or one argument

Answer 1

When you specify your member function, your class must be the left hand side.

B * 4 is equivalent to B.operator* (4). When you say 4 * B, this does not work.

To remedy this, simply use B * 4 instead of 4 * B, or provide an external overload

Matrix operator* (int, const Matrix &);

Then, the 4 * B will match this overload.