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

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