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From: heintze.peewee.enet.dec.com (Sieg Heintze)
Newsgroups: comp.lang.c++
Subject: Multidimensional Arrays accessed with [] operator
Summary: How to implement multidimensional Arrays
Keywords: Arrays, [] operator
Message-ID: <13060@shlump.nac.dec.com>
Date: 3 Jul 90 17:19:22 GMT
Sender: newsdaemon@shlump.nac.dec.com
Organization: Digital Equipment Corporation
Lines: 39

During Spring Semester, I was simulating the write path of a magnetic-optical 
storage (MO) disk.   I needed a five dimenensional array of floats whose 
dimensions would be determined at run time.  I was  also determined to access
the elements with the [] operator regardless of whether I was in a function or 
not!

I wanted to create  a special array class and overload the [] operator.

As you may know, there is a serious problem with C and the default array
syntax for C++. I refer you to page 120 of Stroustrup's "the C++ Programming
Language" where he says you cannot pass arrays, you can only pass pointers and
inside the recieving subprogram you have to compute your own offsets. Even
Bjarne (in the comments) says that this is obscure!

Someone kindly gave an example of using the [] operator to access a pseudo 
array.  This what was done was to use [] to access an array of pointers. So 
for each successive dimension, you have another array of pointers.  Each array 
of pointers is contained an a class that also holds the bounds for that row or 
column.

Well this was very nice and even pratical for two dimensional arrays.  But I 
was afraid to try it with a five dimensional pseudo array!  The redundant 
overhead would be staggering!

How can I efficiently overload [] for a five dimensional pseudo array.

Better yet, how can I efficiently overload [] for a five dimensional real 
array (ie, an contiguous array that does not use pointers to find a element 
given the row and column).

Incidently, for my simulation, I gave up on overloading [] and just used the 
features of C to access entity declared as  "float**** modisk;".   This did 
not, of course, have the bounds checking I wanted.

heintze@genral.enet.dec.com
Digital Equipment Corporation
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