operator over loading: "operator+"must take either zero or one argument

Question

I have a matrix class called IntMatrix

namespace mtm
{
    class IntMatrix
    {
    private:
        int** data;
        int col;
        int row;
    public:
          IntMatrix(int row,int col,int num=0);
         IntMatrix(const IntMatrix& mat);
          //some functions
          IntMatrix ::operator+(int num) const;
          friend IntMatrix operator+(const int &num, const IntMatrix& matrix);
};
//ctor
IntMatrix::IntMatrix(int row,int col, int num) :data(new int*[row]), col(col), row(row)
    {
        for (int i = 0; i < col; i++)
        {
            data[i] = new int[col];
        }
        for (int i = 0; i < row; i++)
        {
            for (int j = 0; j < col); j++)
            {
                data[i][j] = num;
            }
        }
    }
}

I am trying to overload operator+, so that this would work:

//copy ctor
IntMatrix::IntMatrix(const IntMatrix& mat)
{
    data=new int*[mat.row];
    for(int i = 0; i < mat.row; i++) 
    {
        data[i]=new int[mat.col];
    }
    row=mat.row;
    col=mat.col;
    for(int i=0;i<row;i++)
    {
     for(int j=0;j<col;j++)
     {
         data[i][j]=mat.data[i][j];
     }
    }
}

IntMatrix IntMatrix::operator+(int num) const
{
    IntMatrix new_Matrix(*this);
    for(int i=0;i<new_Matrix.row;i++)
    {
        for(int j=0;j<new_Matrix.col;j++)
        {
            new_Matrix.data[i][j]+=num;
        }
    }
    return new_Matrix;
}
// the function I have problem with:
IntMatrix IntMatrix::operator+(const int &num, const IntMatrix& matrix) 
{
    return matrix+num;
}

int main()
{
 mtm::IntMatrix mat(2,1,3);
 mtm::IntMatrix mat2=2+mat;
return 0;
}

how ever no matter what I do I keep getting this error: error: ‘mtm::IntMatrix mtm::IntMatrix::operator+(const int&, const mtm::IntMatrix&)’ must take either zero or one argument IntMatrix IntMatrix::operator+(const int &num, const IntMatrix& matrix)

I tried:

friend IntMatrix operator+(const int &num, const IntMatrix& matrix);
IntMatrix operator+(const int &num, const IntMatrix& matrix);
IntMatrix operator+(const int &num, const IntMatrix& matrix)const;
IntMatrix operator+(int &num, const IntMatrix& matrix);
IntMatrix operator+( int num, const IntMatrix& matrix);

yet I got the same error with all of them, so does any one know what is the correct way to write it?

@molbdnilo this is a reproducible example, I posted the class, the ctor, the function I have problem with , and the main() — raghad
Are you sure that you get that error from the code you posted? — 463035818_is_not_a_number
Your current example (with friend) compiles just right for me, provided that I add a body for that function (and fix typo in constructor) — Yksisarvinen
you posted enough to compile it, but it doesnt reproduce the error: godbolt.org/z/Lqd5xL — 463035818_is_not_a_number

user253751 user253751 · Accepted Answer · 2020-06-25T13:41:18

Declaring a function with friend does not make it part of the class. The int+IntMatrix operator is not IntMatrix::operator+ - it's just operator+.

//        wrong - delete this part
//        vvvvvvvvvvv
IntMatrix IntMatrix::operator+(const int &num, const IntMatrix& matrix) 
{
    return matrix+num;
}

operator over loading: "operator+"must take either zero or one argument

2 Answers