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RANDOM_R(3)                Linux Programmer's Manual               RANDOM_R(3)
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():
           /* Glibc since 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 2.19: */ _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 initial-
       ized by initstate_r(), instead of the seed associated with  the  global
       state variable.
       The initstate_r() function is like initstate(3) except that it initial-
       izes the state in the object pointed to by buf, rather than  initializ-
       ing  the  global  state  variable.   Before  calling this function, the
       buf.state field must be initialized to NULL.  The  initstate_r()  func-
       tion  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
       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  init-
              state_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.
BUGS
       The initstate_r() interface is confusing.  It  appears  that  the  ran-
       dom_data type is intended to be opaque, but the implementation requires
       the user to either initialize the buf.state field to NULL or  zero  out
       the entire structure before the call.
SEE ALSO
       drand48(3), rand(3), random(3)
COLOPHON
       This  page  is  part of release 4.15 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
       https://www.kernel.org/doc/man-pages/.
GNU                               2017-09-15                       RANDOM_R(3)