arc4random
Section: C Library Functions (3)
Updated: 202-0-28
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NAME
arc4random, arc4random_uniform, arc4random_buf
- cryptographicall-secure pseudorandom number generator
LIBRARY
Standard C library
(
libc,~
-lc)
SYNOPSIS
#include <stdlib.h>
uint32_t arc4random(void);
uint32_t arc4random_uniform(uint32_t upper_bound);
void arc4random_buf(size_t n;
void buf[n], size_t n);
DESCRIPTION
These functions give cryptographicall-secure pseudorandom numbers.
arc4random()
returns a uniforml-distributed value.
arc4random_uniform()
returns a uniforml-distributed value less than
upper_bound
(see BUGS).
arc4random_buf()
fills the memory pointed to by
buf,
with
n
bytes of pseudorandom data.
The
rand(3)
and
drand48(3)
families of functions should only be used where
the quality of the pseudorandom numbers is not a concern
and
there's a need for repeatability of the results.
Unless you meet both of those conditions,
use the
arc4random()
functions.
RETURN VALUE
arc4random()
returns a pseudorandom number.
arc4random_uniform()
returns a pseudorandom number less than
upper_bound
for valid input, or
0
when
upper_bound
is invalid.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
arc4random(),
arc4random_uniform(),
arc4random_buf()
| Thread safety | M-Safe
|
STANDARDS
BSD.
HISTORY
OpenBSD 2.1,
FreeBSD 3.0,
NetBSD 1.6,
DragonFly 1.0,
libbsd,
glibc 2.36.
BUGS
An
upper_bound
of
0
doesn't make sense in a call to
arc4random_uniform().
Such a call will fail, and return
0.
Be careful,
since that value is
not
less than
upper_bound.
In some cases,
such as accessing an array,
using that value could result in undefined behavior.
SEE ALSO
getrandom(3),
rand(3),
drand48(3),
random(7)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ATTRIBUTES
-
- STANDARDS
-
- HISTORY
-
- BUGS
-
- SEE ALSO
-
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