Swap bytes.
  Swaps num bytes of src by pairs and stores the result in dest. Useful to change byte order (lower order byte becomes higher, and higher becomes lower) in order to exchange binary data with a machine that uses a different byte order on 2-bytes data types.

Parameters.

src

Address of data to be swapped

dest

Destination location for the swapped data.

num

Number of bytes to be swapped.

Return Value.
  (none)

Portability.
  Not defined in ANSI-C. Supported by some compilers.

Example.

/* swab example */
#include <stdio.h>
#include <stdlib.h>

/* global arrays: destination[] initialized with zeros */
char source [7] = "ABCDEF";
char destination [7];

main ()
{
  swab (source, destination, 6);
  printf ("swab: %s -> %s\n", source, destination);
  return 0;
}

See also.
  atof, strtol, strtoul