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

NAME         top

       random_r,  srandom_r, initstate_r, setstate_r - reentrant random num‐
       ber generator

SYNOPSIS         top

       #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():
           /* Glibc since 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

DESCRIPTION         top

       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         top

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

ERRORS         top

       EINVAL A state array of less than 8 bytes was specified to

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

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

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                   Attribute     Value            │
       │random_r(), srandom_r(),    │ Thread safety │ MT-Safe race:buf │
       │initstate_r(), setstate_r() │               │                  │

CONFORMING TO         top

       These functions are nonstandard glibc extensions.

SEE ALSO         top

       drand48(3), rand(3), random(3)

COLOPHON         top

       This page is part of release 4.09 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

GNU                              2016-03-15                      RANDOM_R(3)