NAME¶

arc4random, arc4random_uniform, arc4random_buf - cryptographically-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(void buf[.n], size_t n);

DESCRIPTION¶

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.

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).

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)