RANDOM_R
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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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 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().
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(),
initstate_r(),
setstate_r()
| Thread safety | MT-Safe race:buf
|
CONFORMING TO
These functions are nonstandard glibc extensions.
BUGS
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.
SEE ALSO
drand48(3),
rand(3),
random(3)
COLOPHON
This page is part of release 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- BUGS
-
- SEE ALSO
-
- COLOPHON
-
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