Re: how to overload subscript of 2D-array

From:
"Axter" <google@axter.com>
Newsgroups:
comp.lang.c++
Date:
10 May 2006 15:31:14 -0700
Message-ID:
<1147300274.207500.65520@j73g2000cwa.googlegroups.com>
DaVinci wrote:

Axter wrote:

DaVinci wrote:

/* how to overload the operation [] ,subscipt of 2D-array?
 * how can I get element through piece[i][j],rather than piece(i)[j]?
 * */
#include"global.h"
using namespace std;
class Piece
{
    public:
    Piece()
    {
    for(size_t i = 0;i<2;i++)
        for(size_t j = 0;j<3;j++)
        {
        piece[i][j] = i+ j;
        }
    for(size_t i=0;i<2;i++)
    {
        std::copy(piece[i],piece[i]+3,ostream_iterator<int>(cout," "));
        cout<<endl;
    }
    cout<<"----------------------"<<endl;
    }
    int* operator()(const int& t)//change operator() to operator[] is
wrong ,why?
    {
    i = t; //
    return piece[i];
    }
    int operator[](const int & t)
    {
    return this->operator()(i)[t];
    }
    private:
    int i;//witchout varible i,how can I implement overload the () , []
or[],[]
    int piece[2][3];
};
//----------------------------------------
int main()
{
    Piece p ;
    for(int i=0;i<2;i++)
    {
    for(int j=0;j<3;j++)
    {
         cout<<p(i)[j]<<" ";//p[i][j],??
    }
    cout<<endl;
    }
}
/*
//output is
0 1 2
1 2 3
----------------------
0 1 2
1 2 3
*/


I recommend against using the method posted in the C++ FAQ.
It recommends you use a non-standard syntax.

If you want to use standard syntax check out the following link for an
example:
http://code.axter.com/dynamic_2d_array.h

However, for most requirements, I recommend using a vector of vector.
Example:
int col = 123;
int row = 456;
vector<vector<int> > My2dArray(col, vector<int>(row));

You can reference both the above vector code and the dynamic_2d_array
class using double index ([][])
My2dArray[0][0] = 99;

Check out the following link for wrapper classes using vector of
vector:
http://www.codeguru.com/forum/showthread.php?t=231046
http://www.codeguru.com/forum/showthread.php?s=&threadid=297838


yes,I know vector<vector<int> > but here

The class Piece 's purpose 's isnot just for 2D-array,it was desiged to
support some other
operation such as void draw_grahic(),
void move_left() and so on.
But I must first Encapsulate the 2d-array int piece[2][3] as private
data.
and supply operator[][] to get it's data,
is there way to overload the operator[] twice to meet my need?


Yes.
Did you look at the first link I posted?
http://code.axter.com/dynamic_2d_array.h

The above link doesn't use vector vector, and it's able to use
operator[] to return a 2D array without using a proxy class.

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