Consider the following code:
func ()
{
long a = 0x12345678;
char *p;
p = (char *) &a;
printf ("%02X\n", *p);
}
On a little-endian machine, this prints the value "0x78"; on a big-endian machine, it prints "0x12". This is one of the big (pardon the pun) reasons why structured programmers generally frown on typecasts.