arc4random(3)                                         Library Functions Manual                                        arc4random(3)

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
       These nonstandard functions are present on several Unix systems.

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)

Linux man-pages 6.03                                         2023-01-05                                               arc4random(3)