Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!columbia!cubmol!ping
From: ping@cubmol.bio.columbia.edu (Shiping Zhang)
Newsgroups: comp.lang.c
Subject: Re: realloc questions
Message-ID: <1990Feb27.215122.10441@cubmol.bio.columbia.edu>
Date: 27 Feb 90 21:51:22 GMT
References: <4563@rouge.usl.edu>
Reply-To: ping@cubmol.bio.columbia.edu (Shiping Zhang)
Distribution: usa
Organization: Dept. of Biology, Columbia Univ., New York, NY
Lines: 49

In article <4563@rouge.usl.edu> pcb@gator.cacs.usl.edu (Peter C. Bahrs) writes:
>This may be a naive discussion but here goes...
>
>I want to create an N (2 for now) dimensional datum of long integers.
>
>    typedef struct a 
>            { int row, col; long **arr} A;
>    A *temp;

    Why don't you declare temp as varible A instead of a point to A,
    and omit the following line of code to allocate space for temp?

>    temp=(A *) calloc (1, sizeof(A));  /* then initialize row and col ... */

>    A->arr=(long *)calloc (A->row, sizeof(long *));
     ^       ^^^^^^         ^

    A (and also in following lines) should be temp and the cast
     should be (long **).

>    for (j=0;j<A->row;j++)
>       A->arr[j] = calloc(col,sizeof(long));
                   ^
    Need cast (long *).
 
>1) I should now be able to index as A->arr[j][k], correct?

    Yes, with the corrections.

>2) or should type A contain long *arr[] instead?
    
    No.  "long *arr[]" is illegal code in C.
 
>Now I want to redimension the type to a new_row and new_col. 
>
>   A->arr=(long *) realloc ((char *)&A->arr, new_row*sizeof(long *));
                ^                    ^
    
  The cast should (long **) and the address operator should NOT be used.
    
>   for (j=0;j<A->new_row;j++)
>       A->arr[j] = realloc(new_col,sizeof(long));
                   ^        ^
    Need cast.

>3) This doesn't work (sometimes).  I understand realloc will retain values
   Not surprising.  With the corrections, it should work all the time.

-ping