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RedHat 9 (Linux i386) - man page for srand (redhat section 3)

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  gen-
       erator  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 random 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  refer-
       ence  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, vol-
       ume 2 (Seminumerical Algorithms), 2nd ed.; Reading, Massachusetts: Addison-Wesley Publish-
       ing 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)


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