random_r, srandom_r, initstate_r, setstate_r - reentrant random number generator
Standard C library (
libc,
-lc)
#include <stdlib.h>
int random_r(struct random_data *restrict buf,
int32_t *restrict result);
int srandom_r(unsigned int seed, struct random_data *buf);
int initstate_r(unsigned int seed, char statebuf[restrict .statelen],
size_t statelen, struct random_data *restrict buf);
int setstate_r(char *restrict statebuf,
struct random_data *restrict buf);
random_r(),
srandom_r(),
initstate_r(),
setstate_r():
/* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 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 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 (), initstate_r (), setstate_r () |
Thread safety |
MT-Safe race:buf |
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 field to NULL or
zero out the entire structure before the call.
drand48(3),
rand(3),
random(3)