CODEWITHSUNDEEP
c++pointersoperator-overloading
vveil
vveil

Reputation: 330

Can't figure out why overloaded operator[] isn't getting called

I got a class Matrix and a class Row. Matrix has as member variable a pointer to a pointer of an object from class Row. I overloaded the operator [] for Matrix and Row. But somehow the overloaded operator from Row is never getting called and I can't figure out why not.

Example Code: matrix.h

class Row
{
    int* value;
    int size;

public:
    int& operator[](int i)
    {
        assert(i >= 0 && i < size);
        return value[i];
    }
};
class Matrix
{
private:
    Row **mat;        // Pointer to "Row"-Vector
    int nrows, ncols;   // Row- and Columnnumber

public:
    Row& Matrix::operator[](int i){
        assert(i >= 0 && i < nrows);
        return *mat[i];
    }
    Row** getMat() {
        return mat;
    }
    // Constructor
    Matrix(int rows, int cols, int value);

};

matrix.cpp

#include "matrix.h"

Matrix::Matrix(int rows, int cols, int value) : nrows(rows), ncols(cols){
    mat = new Row*[rows];

    for(int i = 0; i < rows; i++) {
        mat[i] = new Row(ncols);
        for(int j = 0; j < ncols; j++){
            // the operator-overload of Row[] isn't getting called and I don't get why not
            mat[i][j] = value;
        }
    }
}


int main(){

Matrix m = new Matrix(2, 2, 4);

return 0;

Upvotes: 0

Views: 53

Answers (2)

vveil
vveil

Reputation: 330

So I just figured it out myself. I tried to call the []-operator from Matrix through mat[][], but since mat is a Row** Row& Matrix::operator[](int i) is never getting called.

Upvotes: 1

ivan.ukr
ivan.ukr

Reputation: 3551

mat[i] gives you Row*, and you want to call Row::operator[], but pointer to Row is not dereferenced automatically. So you have to dereference it manually: (*mat[i])[j].

Upvotes: 1

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