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).

       ┌───────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │Interface                                                      │ Attribute     │ Value   │
       ├───────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │arc4random(), arc4random_uniform(), arc4random_buf()           │ Thread safety │ MT-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.

SEE ALSO

       getrandom(3), rand(3), drand48(3), random(7)