Re: Can we override [][] ?

"Jim Langston" <>
Tue, 30 May 2006 19:37:08 -0700
"Cy Edmunds" <> wrote in message

"Jim Langston" <> wrote in message

I wanted to do an operator override for [][] but couldnt' figure out the
syntax. I tried this (code that doesn't compile commented out with //:

class CMyBitmap
   CMyBitmap( int Rows, int Columns ): Rows_( Rows ), Columns_( Columns )
       Data_ = new SPixel[ Rows * Columns ];
       delete[] Data_;

// error C2804: binary 'operator [' has too many parameters
// SPixel& operator[]( const int Row, const int Column )
// {
// return Data_[ Columns_ * Row + Column ];
// }

// error C2092: '[]' array element type cannot be function
// SPixel& operator[][]( const int Row, const int Column )

   SPixel& Pixel( const int Row, const int Column )
       return Data_[ Columns_ * Row + Column ];

   SPixel* Data_;
   int Rows_;
   int Columns_;

   // No copy or assignment yet so disable by making private.
   CMyBitmap ( CMyBitmap const& ) {};
   CMyBitmap& operator=( CMyBitmap const& ) {};


Can we override 2d array access?

You should declare your operator as

something operator [] (int Row);

Then "something" must define

SPixel &operator [] (int Column);

The question is, what is "something"? The best thing is probably to make
it a separate class. However, a well known cheat is to make "something" an
SPixel*, which automatically provides this second operator by the usual
rules for subscripting a pointer. Hence

SPixel *operator [] (int Row) {return Row * Columns_;}

will do it!

This is an excellant solution, but I can't check for column overflow. I
think I'll keep the existing solution I have right now, but keep your's in
mind for other classes.


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