realloc questions

[William P. Kaufman]

Just one more thing to add to the discussion,...

To remind you (I added the previous corrections someone suggested to the code):

In article <4563 at rouge.usl.edu> pcb at gator.cacs.usl.edu (Peter C. Bahrs) writes:
>
>    typedef struct a 
>            { int row, col; long **arr} A;
>    A *temp;
>
>    temp=(A *) calloc (1, sizeof(A));  /* then initialize row and col ... */
>    temp->arr=(long *)calloc (temp->row, sizeof(long *));
>    for (j=0;j<temp->row;j++)
>       temp->arr[j] = calloc(col,sizeof(long));
>
>1) I should now be able to index as temp->arr[j][k], correct?
>2) or should type A contain long *arr[] instead?

	That would be fine as long as you know the number of rows
ahead of time, as in "long *arr[30]", or some such.  Otherwise, "type
var[]" is only good if the variable is actually declared somewhere
else--say in an extern definition, or as a function parameter.  The
compiler needs to know at compilation time how large the objects are.
	As it is, it's just fine.

>Now I want to redimension the type to a new_row and new_col. 
>
>   temp->arr=(long *) realloc ((char *)&temp->arr, new_row*sizeof(long *));
>   for (j=0;j<temp->new_row;j++)
>       temp->arr[j] = realloc(new_col,sizeof(long));

	AUUGGGHHH!!  Sorry, I just recently had to re-write someone's
code that did this sort of thing.  You're re-allocating temp->arr
before you re-allocate temp->arr[j]! Just switch the order of the
realloc() calls and you should be fine.

	Happy hunting!

				-Bill Kaufman
				Nowhere you can get to by e-mail