If you want the size of an array to vary during the execution of the program it must be dynamically allocated using malloc() or calloc(). I put together a small example of this in which when the array is resized, the contents are persisted as possible. This example elides error handling (such as an allocation failing) etc. but it should get you started.
I should mention that a potentially easier solution may be to use Handles instead of managing the array yourself; doing this is not a portable solution but it is a nice alternative that would do most of this management for you.
#define MIN(a, b) ((a) < (b) ? (a) : (b))
// *pArray can be NULL, oldSize or newSize can be zero
// newSize == zero will free up the array
void ChangeArraySize(int **pArray, int oldSize, int newSize)
{
int *newArray;
// allocate the space for the new array unless the size is <= 0
if (newSize > 0)
newArray = malloc(newSize * sizeof(int));
else
newArray = NULL;
// if an array already exists
if (*pArray)
{
// copy elements if necessary
if (oldSize > 0 && newSize > 0)
memcpy (*pArray, newArray, MIN(oldSize, newSize) * sizeof(int));
// free up the old array
free(*pArray);
}
// drop the new array in
*pArray = newArray;
}
int main(void)
{
int *array = NULL, arraySize = 0, i ;
ChangeArraySize(&array, arraySize, 100); // initial array allocation
arraySize = 100; // keep track of the current size
for (i = 0; i < arraySize; ++i)
array[i] = i;
ChangeArraySize(&array, arraySize, 50); // elements 0-49 are maintained
arraySize = 50;
for (i = 0; i < arraySize; ++i) // prints 0..49
printf("%d\n", i);
ChangeArraySize(&array, arraySize, 0); // free up
return 0;
}
Message Edited by Alex D on 07-02-2005 11:06 PM
