bsdRandomEx.c

/**
   @file      bsdRandomEx.c
   @author    Mitch Richling <http://www.mitchr.me/>
   @Copyright Copyright 2004 by Mitch Richling.  All rights reserved.
   @brief     Example for the BSD random/srandom functions@EOL
   @Keywords  random bsd 
   @Std       C89

              In BSD 4.2 the random() and srandom() functions appeared
              as a better replacement for the ISO C rand()/srand()
              functions and the family of rand48() functions.
              random() has a period of roughly 16*((2**31)-1), and
              returns long integers roughly distributed as
              U[0, (2**31)-1].  In addition to replacing rand() and
              srand(), the BSD developers also provided an interface
              to the random device via srandomdev() and a more
              sophisticated state management system via setstate() and
              initstate().  The last two functions are not
              demonstrated here.  Note that random() produces better
              random numbers than rand(), but one should still use
              more secure sources for cryptographic needs and better
              studied sources for serious simulation.
              
*/

#include <stdio.h>              /* I/O lib         ISOC  */
#include <stdlib.h>             /* Standard Lib    ISOC  */

int main(int argc, char *argv[]);

int main(int argc, char *argv[]) {

  int  i;
  long aRand;

  /* Set the seed for the random number */
  srandom(1234);

  printf("Five random long integers in U[0, (2**31)-1]\n");
  for(i=0; i<5; i++) {
    aRand = random();
    printf("%3d %15ld\n", i, aRand);
  }

  /* Use the random number device to seed the generator.  Note that
     this can lead to states no reproducible via srandom() */
  srandomdev();

  printf("Five random long integers in U[0, (2**31)-1]\n");
  for(i=0; i<5; i++) {
    aRand = random();
    printf("%3d %15ld\n", i, aRand);
  }

  return 0;
}