Unix/Linux Go Back    


Linux 2.6 - man page for random (linux section 3)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)


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

NAME
       random, srandom, initstate, setstate - random number generator

SYNOPSIS
       #include <stdlib.h>

       long int random(void);

       void srandom(unsigned int seed);

       char *initstate(unsigned int seed, char *state, size_t n);
       char *setstate(char *state);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       random(), srandom(), initstate(), setstate():
	   _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
	   _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

DESCRIPTION
       The random() function uses a nonlinear additive feedback random number generator employing
       a default table of size 31 long integers to return successive pseudo-random numbers in the
       range from 0 to RAND_MAX.  The period of this  random  number  generator  is  very  large,
       approximately 16 * ((2^31) - 1).

       The  srandom()  function sets its argument as the seed for a new sequence of pseudo-random
       integers to be returned by random().  These sequences are repeatable by calling	srandom()
       with the same seed value.  If no seed value is provided, the random() function is automat-
       ically seeded with a value of 1.

       The initstate() function allows a state array state to be initialized for use by random().
       The  size of the state array n is used by initstate() to decide how sophisticated a random
       number generator it should use--the larger the state array, the better the random  numbers
       will  be.   seed  is the seed for the initialization, which specifies a starting point for
       the random number sequence, and provides for restarting at the same point.

       The setstate() function changes the state array used by the random() function.  The  state
       array  state  is  used  for random number generation until the next call to initstate() or
       setstate().  state must first have been initialized using initstate() or be the result  of
       a previous call of setstate().

RETURN VALUE
       The  random()  function	returns  a  value between 0 and RAND_MAX.  The srandom() function
       returns no value.

       The initstate() function returns a pointer to the previous state array.	On  error,  errno
       is set to indicate the cause.

       On  success,  setstate()  returns  a  pointer  to  the previous state array.  On error, it
       returns NULL, with errno set to indicate the cause of the error.

ERRORS
       EINVAL The state argument given to setstate() was NULL.

       EINVAL A state array of less than 8 bytes was specified to initstate().

CONFORMING TO
       4.3BSD, POSIX.1-2001.

NOTES
       Current "optimal" values for the size of the state array n are 8, 32,  64,  128,  and  256
       bytes;  other amounts will be rounded down to the nearest known amount.	Using less than 8
       bytes will cause an error.

       This function should not be used in cases where multiple  threads  use  random()  and  the
       behavior should be reproducible.  Use random_r(3) for that purpose.

       Random-number  generation  is  a complex topic.	Numerical Recipes in C: The Art of Scien-
       tific Computing (William H. Press, Brian P. Flannery, Saul A. Teukolsky, William  T.  Vet-
       terling;  New York: Cambridge University Press, 2007, 3rd ed.)  provides an excellent dis-
       cussion of practical random-number generation issues in Chapter 7 (Random Numbers).

       For a more theoretical discussion which also covers many practical issues  in  depth,  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.

BUGS
       According to POSIX, initstate() should return NULL on error.  In the glibc implementation,
       errno is (as specified) set on error, but the function does not return NULL.

SEE ALSO
       drand48(3), rand(3), random_r(3), srand(3)

COLOPHON
       This page is part of release 3.55 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at
       http://www.kernel.org/doc/man-pages/.

GNU					    2013-04-19					RANDOM(3)
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 04:57 PM.