operator overloading [][] 2d array c++

问题

I have a 2D array and I want to define a function that returns the value of the index that the user gives me using operator overloading. In other words:

void MyMatrix::ReturnValue()
{
    int row = 0, col = 0;
    cout << "Return Value From the last Matrix" << endl;
    cout << "----------------------------------" << endl;
    cout << "Please Enter the index: [" << row << "][" << col << "] =" << ((*this).matrix)[row][col] << endl;
}

The operation ((*this).matrix)[row][col] should return an int. I have no idea how to build the operator [][].
Alternatively, I could concatenate a couple of calls to the operator [], but I didn't succeed in it, because the first call to that operaror will return int* and the second one will return int, and it compel to build another operator, and I dont want to do that.

What can I do? Thank you,

回答1:

Simply, such an operator does not exist, so you can not overload it.

A possible solution is to define two classes: the Matrix and the Row.
You can define the operator[] of a Matrix so that it returns a Row, then define the same operator for the Row so that it returns an actual value (int or whatever you want, your Matrix could be also a template).
This way, the statement myMatrix[row][col] will be legal and meaningful.

The same can be done in order to assign a new Row to a Matrix or to change a value in a Row.

* EDIT *

As suggested in the comments, also you should take in consideration to use operator() instead of operator[] for such a case.
This way, there wouldn't be anymore the need for a Row class too.

回答2:

You can define your own operator [] for the class. A straightforward approach can look the following way

#include <iostream>
#include <iomanip>

struct A
{
    enum { Rows = 3, Cols = 4 };
    int matrix[Rows][Cols];
    int ( & operator []( size_t i ) )[Cols]
    {
        return matrix[i];
    }
};

int main()
{
    A a;

    for ( size_t i = 0; i < a.Rows; i++ )
    {
        for ( size_t j = 0; j < a.Cols; j++ ) a[i][j] = a.Cols * i + j;
    }


    for ( size_t i = 0; i < a.Rows; i++ )
    {
        for ( size_t j = 0; j < a.Cols; j++ ) std::cout << std::setw( 2 ) << a[i][j] << ' ';
        std::cout << std::endl;
    }
}

The program output is

 0  1  2  3 
 4  5  6  7 
 8  9 10 11

回答3:

#include<iostream>
using namespace std;
class matrix
{
     int **arr;
     int r;
     int c;
     public:
    /* another code*/
     class row
    {
        matrix &_a;
        int _i;
        public:
        row(matrix &a,int i) : _a(a),_i(i){}
        int operator[](int j) {return _a.arr[_i][j];}
     };
     row operator[](int i)
    {   
        return row(*this,i);
     }
 };

This could help you

来源：https://stackoverflow.com/questions/34461416/operator-overloading-2d-array-c

标签

c++

arrays

operator-overloading

operator-keyword