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
       automatically 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().

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌────────────────────────┬───────────────┬─────────┐
       │Interface               │ Attribute     │ Value   │
       ├────────────────────────┼───────────────┼─────────┤
       │random(), srandom(),    │ Thread safety │ MT-Safe │
       │initstate(), setstate() │               │         │
       └────────────────────────┴───────────────┴─────────┘

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, 4.3BSD.

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
       Scientific Computing (William H. Press, Brian P. Flannery, Saul A. Teukolsky,  William  T.
       Vetterling;  New  York:  Cambridge University Press, 2007, 3rd ed.)  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,  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), getrandom(2), rand(3), random_r(3), srand(3)

COLOPHON

       This page is part of release 4.04 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.