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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | BUGS | SEE ALSO | COLOPHON |
RANDOM_R(3) Linux Programmer's Manual RANDOM_R(3)
random_r, srandom_r, initstate_r, setstate_r - reentrant random num‐
ber generator
#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 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().
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
initstate_r().
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
attributes(7).
┌────────────────────────────┬───────────────┬──────────────────┐
│Interface │ Attribute │ Value │
├────────────────────────────┼───────────────┼──────────────────┤
│random_r(), srandom_r(), │ Thread safety │ MT-Safe race:buf │
│initstate_r(), setstate_r() │ │ │
└────────────────────────────┴───────────────┴──────────────────┘
These functions are nonstandard glibc extensions.
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.
drand48(3), rand(3), random(3)
This page is part of release 4.12 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 2017-03-13 RANDOM_R(3)
Pages that refer to this page: random(3)