Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!usc!jarthur!nntp-server.caltech.edu!suncub.bbso.caltech.edu!EYCHANER
From: eychaner@suncub.bbso.caltech.edu (Amateurgrammer)
Newsgroups: comp.lang.c
Subject: Re: More 2D array woes...
Message-ID: <1991Mar4.064805.22220@nntp-server.caltech.edu>
Date: 4 Mar 91 06:48:05 GMT
References: <1991Mar3.235114.12154@nntp-server.caltech.edu>,<1002@caslon.cs.arizona.edu>,<1991Mar4.030849.16054@nntp-server.caltech.edu>
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Reply-To: eychaner@suncub.bbso.caltech.edu
Organization: Big Bear Solar Observatory, Caltech
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A followup to my followup...

eychaner@suncub.bbso.caltech.edu (Amateurgrammer) writes:
>>eychaner@suncub.bbso.caltech.edu writes:
>>>Here we go again, warm up the flame guns...
>>>
>>>Ok, suppose I have an array like
>>>    char strings[NUMBER][SIZE];
>>>How do I add more strings to this array, i.e. make it larger, portably and
>>>easily.  I can't realloc it, since it's not a pointer!  Argh!

Some poeple have complained that this is in the FAQ; well, I did read the
FAQ beforehand and the solutions it gives either result in a non-contiguous
array or make it VERY DIFFICULT to make the array larger.  The following
solution is MUCH better (though a little more opaque) than the ones in the
FAQ, and IMHO should be included there.

>Well, actually, Chris Torek (torek@ee.lbl.gov) pointed out that the "cheap
>and dirty way" (my phrase, not his) of doing this is to declare
>
>      char (*dynamic)[N];
>      dynamic = (char (*)[N]) malloc (M * N);
>
>where N is the number of items in each row of the array, and M is the
>number of rows.  This array can then be accessed by
>
>      dynamic [x][y] = SOME_CHAR;
>
>and reallocated by
>
>      dynamic = realloc (dynamic, NEWSIZE * N);
>
>so you CAN do it in C.  It's just a little tricky.  Ok, a LOT tricky.

Also, I would like to point out that to call realloc (to add a new row to 
the array) with a function could be (I HOPE I got this right, PLEASE):

      void increase_array (char (**array)[N], int *num_of_elements)
      {
      *array = (char (*)[N]) realloc (*array, ++(*num_of_elements) * N);
      }

This is called as:

      char (*dynamic)[N]; 
      int num_elem;
      increase_array (&dynamic, &num_elem);

If your compiler lets you call realloc() with NULL, set dynamic = NULL and
num_elem to 0 to add the FIRST element.
This is VERY powerful, and is MUCH better than the FAQ answer.  It is also
EXACTLY what I wanted.  So the FAQ is not the be-all and end-all of C.
Neither is C++ (which some people suggested).
:-)
Glenn Eychaner - Big Bear Solar Observatory - eychaner@suncub.bbso.caltech.edu
"You Have the Right to Remain DEAD."
					-The Simpsons