realloc woes

[John C. Lusth]

I have a need to store some information in an array, but don't want to
have an arbitrary limit on the size of the array.  I came up with the
following scheme to successively increase the size of the array as needed.
The code has been excerpted and edited; I hope I haven't introduced errors.

char	**Strings;

if (i >= StringCount) {  /* str is not already in the pool */

    if (SlotsLeft <= 0) {

	if (FirstTime) {
	    Strings = (char **) malloc(BankSize * sizeof(char *));
	    FirstTime = 0;
	    }
	else
	    Strings = (char **) realloc(Strings, (i+BankSize) * sizeof(char *));

	SlotsLeft = BankSize;
	}
    
    Strings[i] = str;	/* here's where I trash somebody else */
	
    ++StringCount;
    --SlotsLeft;
    }

In the program I am working on, I have four arrays I expand this way.
Unfortunately, at one point in saving a string, I trash the memory
used by another expanding array.  My questions are:

    1)  is there a better way to have arrays that can grow without bound?

    2)  if not, am I using realloc correctly?  I suspect realloc is
	the culprit because if I set BankSize high enough, the problem goes
	away.  BTW, in the actual code, I check the returns of malloc
	and realloc.

    3)  if I am using realloc correctly, what's the best way for finding
	out how I'm ending up with some shared memory locations?

I am running SUN OS 4.1.1 using cc.

john
--
John C. Lusth, Becton Dickinson Research Center, RTP, NC, jcl at bdrc.bd.com