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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(): _SVID_SOURCE || _BSD_SOURCE

DESCRIPTION
       These  functions  are  the reentrant equivalents of the functions described in ran-
       dom(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.  The generated random number is returned in the argu-
       ment 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, 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, or -1 on 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.

CONFORMING TO
       These functions are non-standard glibc extensions.

SEE ALSO
       drand48(3), rand(3), random(3)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the project, and information about reporting bugs, can be found at  http://www.ker-
       nel.org/doc/man-pages/.



GNU                               2008-03-07                       RANDOM_R(3)

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