Change the size of an allocated part of memory. The memory must
have been allocated by malloc() or calloc(). If you reduce the
size, the old contents will be lost. If you enlarge the size,
the new contents will be undefined.
INPUTS
oldmen
What you got from malloc() or calloc().
size
The new size.
RESULT
A pointer to the allocated memory or NULL. If you don't need the
memory anymore, you can pass this pointer to free(). If you don't,
the memory will be freed for you when the application exits.
NOTES
If you get NULL, the memory at oldmem will not have been freed and
can still be used.