Re: Can we override [][] ?

From:
"Jim Langston" <tazmaster@rocketmail.com>
Newsgroups:
comp.lang.c++
Date:
Tue, 30 May 2006 17:56:34 -0700
Message-ID:
<eR5fg.138$212.127@fe04.lga>
"Mike Wahler" <mkwahler@mkwahler.net> wrote in message
news:5I5fg.9653$y4.1299@newsread2.news.pas.earthlink.net...

"Jim Langston" <tazmaster@rocketmail.com> wrote in message
news:KB5fg.137$212.111@fe04.lga...

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
{
public:
   CMyBitmap( int Rows, int Columns ): Rows_( Rows ), Columns_( Columns )
   {
       Data_ = new SPixel[ Rows * Columns ];
   }
   ~CMyBitmap()
   {
       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 ];
   }

private:
   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?


Certainly. But...
[][] is not an operator, it's two instances of the single
operator []. If you have your operator[] do the 'right
thing', you shouldn't have any problems using expressions
such as x[], x[][], x[][][], etc. Post back if you need
more help or an example.


I had goggled for operator[] but goggle doesn't seem to index special
characters (such as '[') so the hits weren't very orderly and it took me a
long time to even find the syntax for [] My manual didn't give me any
examples, time to get a new manual.

I would need an example please, as I don't know how to override[] to accept
two paramters but you seem to indicate it is two instances of []. What is
the 'right thing' or can you direct me to a web page on the subject? As I
said, in this case Google was not my friend.

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