NAME

       random_r, srandom_r, initstate_r, setstate_r - reentrant random number generator

SYNOPSIS

       #include <stdlib.h>

       int random_r(struct random_data *buf, int32_t *result);

       int srandom_r(unsigned int seed, struct random_data *buf);

       int initstate_r(unsigned int seed, char *statebuf,
                       size_t statelen, struct random_data *buf);
       int setstate_r(char *statebuf, struct random_data *buf);

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

       random_r(), srandom_r(), initstate_r(), setstate_r():
           _SVID_SOURCE || _BSD_SOURCE

DESCRIPTION

       These  functions  are  the  reentrant equivalents of the functions described in random(3).
       They are suitable for use in multithreaded programs where each thread needs to  obtain  an
       independent, reproducible sequence of random numbers.

       The  random_r() function is like random(3), except that instead of using state information
       maintained in a global variable, it uses the state information in the argument pointed  to
       by  buf,  which  must  have  been  previously initialized by initstate_r().  The generated
       random number is returned in the argument result.

       The srandom_r() function is like srandom(3), except that it initializes the seed  for  the
       random  number  generator whose state is maintained in the object pointed to by buf, which
       must have been previously initialized by initstate_r(), instead  of  the  seed  associated
       with the global state variable.

       The  initstate_r()  function  is like initstate(3) except that it initializes the state in
       the object pointed to by buf, rather than initializing the global state variable.

       The setstate_r() function is like setstate(3) except that it modifies  the  state  in  the
       object pointer to by buf, rather than modifying the global state variable.

RETURN VALUE

       All  of  these functions return 0 on success.  On error, -1 is returned, with errno set to
       indicate the cause of the error.

ERRORS

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

       EINVAL The statebuf or buf argument to setstate_r() was NULL.

       EINVAL The buf or result argument to random_r() was NULL.

ATTRIBUTES

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

       ┌────────────────────────────┬───────────────┬──────────────────┐
       │Interface                   │ Attribute     │ Value            │
       ├────────────────────────────┼───────────────┼──────────────────┤
       │random_r(), srandom_r(),    │ Thread safety │ MT-Safe race:buf │
       │initstate_r(), setstate_r() │               │                  │
       └────────────────────────────┴───────────────┴──────────────────┘

CONFORMING TO

       These functions are nonstandard glibc extensions.

SEE ALSO

       drand48(3), rand(3), random(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/.