arc4random(3) - Linux manual page (original) (raw)

arc4random(3) Library Functions Manual arc4random(3)

NAME top

   arc4random, arc4random_uniform, arc4random_buf -
   cryptographically-secure pseudorandom number generator

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <stdlib.h>**

   **uint32_t arc4random(void);**
   **uint32_t arc4random_uniform(uint32_t** _upperbound_**);**
   **void arc4random_buf(void** _buf_**[.**_n_**], size_t** _n_**);**

DESCRIPTION top

   These functions give cryptographically-secure pseudorandom
   numbers.

   **arc4random**() returns a uniformly-distributed value.

   **arc4random_uniform**() returns a uniformly-distributed value less
   than _upperbound_ (see BUGS).

   **arc4random_buf**() fills the memory pointed to by _buf_, with _n_ bytes
   of pseudorandom data.

   The [rand(3)](../man3/rand.3.html) and [drand48(3)](../man3/drand48.3.html) 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 top

   **arc4random**() returns a pseudorandom number.

   **arc4random_uniform**() returns a pseudorandom number less than
   _upperbound_ for valid input, or **0** when _upperbound_ is invalid.

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────────┼───────────────┼─────────┤
   │ **arc4random**(), **arc4random_uniform**(),  │ Thread safety │ MT-Safe │
   │ **arc4random_buf**()                     │               │         │
   └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

   BSD.

HISTORY top

   OpenBSD 2.1, FreeBSD 3.0, NetBSD 1.6, DragonFly 1.0, libbsd, glibc
   2.36.

BUGS top

   An _upperbound_ 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 _upperbound_.  In some
   cases, such as accessing an array, using that value could result
   in undefined behavior.

SEE ALSO top

   **getrandom**(3), [rand(3)](../man3/rand.3.html), [drand48(3)](../man3/drand48.3.html), [random(7)](../man7/random.7.html)

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Linux man-pages 6.10 2024-11-17 arc4random(3)