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


     random_r,  srandom_r, initstate_r, setstate_r - reentrant random number


     #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


     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().


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


     EINVAL A  state  array  of  less  than  8  bytes was specified to init-
     EINVAL The statebuf or buf argument to setstate_r() was NULL.
     EINVAL The buf or result argument to random_r() was NULL.


     For  an  explanation  of  the  terms  used   in   this   section,   see
     allbox;  lbw27  lb  lb l l l.  Interface Attribute Value T{ random_r(),
     initstate_r(), setstate_r() T}   Thread safety  MT-Safe race:buf


     These functions are nonstandard glibc extensions.


     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.


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


     This  page  is  part of release 4.16 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 2017-09-15 RANDOM_R(3)

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