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 |
| Thread safety | MT-Safe |
BSD.
OpenBSD 2.1, FreeBSD 3.0, NetBSD 1.6, DragonFly 1.0, libbsd, glibc 2.36.
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.