arc4random, arc4random_uniform, arc4random_buf - cryptographically-secure
pseudorandom number generator
Standard C library (
libc,
-lc)
#include <stdlib.h>
uint32_t arc4random(void);
uint32_t arc4random_uniform(uint32_t upper_bound);
void arc4random_buf(void buf[.n], size_t n);
These functions give cryptographically-secure pseudorandom numbers.
arc4random() returns a uniformly-distributed value.
arc4random_uniform() returns a uniformly-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.
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.
For an explanation of the terms used in this section, see
attributes(7).
| Interface |
Attribute |
Value |
| arc4random (), arc4random_uniform (), arc4random_buf () |
Thread safety |
MT-Safe |
These nonstandard functions are present on several Unix systems.
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.
getrandom(3),
rand(3),
drand48(3),
random(7)