Name
arc4random, arc4random_uniform, arc4random_buf - cryptographically-secure pseudorandom number generatorLibrary
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 |
| T} | 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 thanupper_bound. In some cases, such as accessing an array, using that value could result in Undefined Behavior.