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.  Before calling this
       function, the buf.state field must be initialized to NULL.  The
       initstate_r() function records a pointer to the statebuf argument
       inside the structure pointed to by buf.  Thus, statebuf should not be
       deallocated so long as buf is still in use.  (So, statebuf should
       typically be allocated as a static variable, or allocated on the heap
       using malloc(3) or similar.)

       The setstate_r() function is like setstate(3) except that it modifies
       the state in the object pointed to by buf, rather than modifying the
       global state variable.  state must first have been initialized using
       initstate_r() or be the result of a previous call of setstate_r().

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.

BUGS         top

       The initstate_r() interface is confusing.  It appears that the
       random_data type is intended to be opaque, but the implementation
       requires the user to either initialize the buf.state file to NULL or
       zero out the entire structure before the call.

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 4.10 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                              2017-03-13                      RANDOM_R(3)