Generating random numbers with Swift

Question

I need to generate a random number.

It appears the arc4random function no longer exists as well as the arc4random_uniform function.

The options I have are arc4random_stir(), arc4random_buf(UnsafeMutablePointer<Void>, Int), and arc4random_addrandom(UnsafeMutablePointer<UInt8>, Int32).

I can't find any docs on the functions and no comments in the header files give hints.

Answer 1

===== Swift 4.2 / Xcode 10 =====

let randomIntFrom0To10 = Int.random(in: 1..<10)
let randomFloat = Float.random(in: 0..<1)

// if you want to get a random element in an array
let greetings = ["hey", "hi", "hello", "hola"]
greetings.randomElement()

Under the hood Swift uses arc4random_buf to get job done.

===== Swift 4.1 / Xcode 9 =====

arc4random() returns a random number in the range of 0 to 4 294 967 295

drand48() returns a random number in the range of 0.0 to 1.0

arc4random_uniform(N) returns a random number in the range of 0 to N - 1

Examples:

arc4random() // => UInt32 = 2739058784
arc4random() // => UInt32 = 2672503239
arc4random() // => UInt32 = 3990537167
arc4random() // => UInt32 = 2516511476
arc4random() // => UInt32 = 3959558840

drand48() // => Double = 0.88642843322303122
drand48() // => Double = 0.015582849408328769
drand48() // => Double = 0.58409022031727176
drand48() // => Double = 0.15936862653180484
drand48() // => Double = 0.38371587480719427

arc4random_uniform(3) // => UInt32 = 0
arc4random_uniform(3) // => UInt32 = 1
arc4random_uniform(3) // => UInt32 = 0
arc4random_uniform(3) // => UInt32 = 1
arc4random_uniform(3) // => UInt32 = 2

arc4random_uniform() is recommended over constructions like arc4random() % upper_bound as it avoids "modulo bias" when the upper bound is not a power of two.