redhat man page for srand

RAND(3) 						     Linux Programmer's Manual							   RAND(3)

NAME
       rand, srand - random number generator.

SYNOPSIS
       #include <stdlib.h>

       int rand(void);

       void srand(unsigned int seed);

DESCRIPTION
       The rand() function returns a pseudo-random integer between 0 and RAND_MAX.

       The  srand() function sets its argument as the seed for a new sequence of pseudo-random integers to be returned by rand().  These sequences
       are repeatable by calling srand() with the same seed value.

       If no seed value is provided, the rand() function is automatically seeded with a value of 1.

RETURN VALUE
       The rand() function returns a value between 0 and RAND_MAX.  The srand() returns no value.

NOTES
       The versions of rand() and srand() in the Linux C Library use the same random number generator as random() and  srandom(),  so  the  lower-
       order bits should be as random as the higher-order bits.  However, on older rand() implementations, the lower-order bits are much less ran-
       dom than the higher-order bits.

       In Numerical Recipes in C: The Art of Scientific Computing (William H. Press, Brian P. Flannery, Saul A. Teukolsky, William T.  Vetterling;
       New York: Cambridge University Press, 1992 (2nd ed., p. 277)), the following comments are made:
	      "If you want to generate a random integer between 1 and 10, you should always do it by using high-order bits, as in

		     j=1+(int) (10.0*rand()/(RAND_MAX+1.0));

	      and never by anything resembling

		     j=1+(rand() % 10);

	      (which uses lower-order bits)."

       Random-number  generation  is  a  complex topic.  The Numerical Recipes in C book (see reference above) provides an excellent discussion of
       practical random-number generation issues in Chapter 7 (Random Numbers).

       For a more theoretical discussion which also covers many practical issues in depth, please see Chapter 3  (Random  Numbers)  in	Donald	E.
       Knuth's	The  Art  of Computer Programming, volume 2 (Seminumerical Algorithms), 2nd ed.; Reading, Massachusetts: Addison-Wesley Publishing
       Company, 1981.

CONFORMING TO
       SVID 3, BSD 4.3, ISO 9899

SEE ALSO
       random(3), srandom(3), initstate(3), setstate(3)

GNU
								    1995-05-18								   RAND(3)