Man page - arc4random(3)

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Manual

arc4random

NAME
LIBRARY
SYNOPSIS
DESCRIPTION
RETURN VALUE
ATTRIBUTES
STANDARDS
HISTORY
BUGS
SEE ALSO

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).

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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)