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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.