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matrix operator overloading

Started by skitzo_smurf Jul 11, 2000 at 4:36 PM 4 replies 250+ views

Original Post

Jul 11, 2000 at 4:36 PM

Say I had a simple class such as this: class matrix { public: matrix(int rows, int cols); //allocate a rows x cols matrix //etc, etc.... private: int **theMatrix; //will be allocated dynamically int rows; int cols; }; How do you overload the [] operator to properly do this: matrix someMatrix(5,5); //make a 5 x 5 matrix //do whatever...... cout << someMatrix[2][4] << endl; I know how to do it with a single dimension array, but how do you do this with a two dimension array? thanks, skitzo_smurf Edited by - skitzo_smurf on 7/11/00 4:37:20 PM Edited by - skitzo_smurf on 7/11/00 5:45:21 PM

skitzo_smurf

Author

skitzo_smurf

Jul 11, 2000 at 5:53 PM

could someone please help me. I dont mean to be a pest, but I have to go soon and this is really bothering me. I know when you do this with a single dimension array you just overload the [] operator like this....

class matrix //example does not really represent a matrix now
{
public:
matrix(int Width) : width(Width) { data = new int[width]; }

//other stuff
//just return the address of data[x]
int &operator [](int x) { return data[x]; }

private:
int *data; //pointer to a dynamically allocated array
int width;
};

then you could say

matrix someMatrix(5);

//later on....
cout << someMatrix[3] << endl;

please help, and if im doing something wrong here then please tell me.

thanks,
skitzo_smurf

Pouya

203

Pouya

Jul 11, 2000 at 6:08 PM

    
class matrix
{
public:
    matrix(int w, int h) : width(w), height(h) 
    {
        data = new (int*)[ width ];
        for (int i=0;i<width;i++)
            data[ i ] = new int[ height ];
    }

    int* operator [](int x)
    {
        return data[ x ];
    } 

private:
    int **data;
    int width, height;
};

there!
matrix[ i ] return an int* as the result, and that int* is equvalent to an int[] iself.
so saying matrix[ i ][ j ], first calls matrix[ i ] to get the pointer fot data and then it references to element j ([ j ]) in that array which gives you data[ i ][ j ]. get it?

----------------
- Pouya / FOO!!!
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skitzo_smurf

Author

skitzo_smurf

Jul 11, 2000 at 6:12 PM

thank you very much for the help pouya! I will try immediately.
btw how do you put code in a window like that on this forum?

skitzo_smurf

RWarden

Jul 11, 2000 at 6:17 PM

I don''t remember if this is legal, but give it a shot:

int matrix::operator[] ( int row, int col )

By the way you might want to have the overloaded [] operator return a reference to the int. That way you could do this:

matrix[x][y] = z;

just a thought =)
-RWarden (roberte@maui.net)

Pouya

203

Pouya

Jul 11, 2000 at 7:14 PM

quote:
Original post by skitzo_smurf

thank you very much for the help pouya! I will try immediately.
btw how do you put code in a window like that on this forum?

skitzo_smurf

put it in [ source ] and [ /source ] tags (don''t put the spaces there btw)

----------------
- Pouya / FOO!!!
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