1	/* byteSwap.c
   2	   This program is to show how to swap bytes in a numeric variable for the
   3	   purposes of solving the byte ordering issues due to the difference in 
   4	   implementations on big-endian and little-endian machines.
     
   5	   The key point illustrated in byteSwap() is how to treat an integer as a 
   6	   character array, so that bytes in the array can be swapped.
   7	*/
     
   8	#include <stdio.h>
   9	#include <string.h>
     
  10	byteSwap(int in, int *out)
  11	{
  12	  int i, pos, siz = sizeof(int);
  13	  char temp, cary[siz];
     
  14	  bcopy((char *)&in, cary, siz);      /* cast and copy an int to a char array */
  15	  pos = siz - 1;
  16	  for (i = 0; i < siz/2; i++) {       /* swap bytes in this char array */
  17	      temp = cary[i];
  18	      cary[i] = cary[pos];
  19	      cary[pos--] = temp;
  20	  }
  21	  bcopy(cary, (char *)out, siz);      /* copy the swapped cary to an int */
  22	}  /* byteSwap */
     
  23	/* A driver to test byteSwap()
  24	   The following numbers show the values before and after byte swaps.
  25	  
  26	   From  |00000100|00000011|00000010|00000001|   -- 67,305,985
  27	   To    |00000001|00000010|00000011|00000100|   -- 16,909,060
  28	*/
     
  29	int main()
  30	{
  31	  union {
  32	      int i;
  33	      short s[2];
  34	  } si;
  35	  int i;
     
  36	  si.s[0] = 0x0201;                   /* |00000010|00000001| */
  37	  si.s[1] = 0x0403;                   /* |00000100|00000011| */
     
  38	  printf("Before swap: %d\n", si.i);
  39	  byteSwap(si.i, &i);
  40	  printf("After swap: %d\n", i);
  41	} /* driver */
     
[pluto:~] byteSwap
Before swap: 67305985
After swap: 16909060