Generating random numbers with Swift

问题

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.

回答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.

回答2:

You could try as well:

let diceRoll = Int(arc4random_uniform(UInt32(6)))

I had to add "UInt32" to make it work.

回答3:

Just call this function and provide minimum and maximum range of number and you will get a random number.

eg.like randomNumber(MIN: 0, MAX: 10) and You will get number between 0 to 9.

func randomNumber(MIN: Int, MAX: Int)-> Int{
    return Int(arc4random_uniform(UInt32(MAX-MIN)) + UInt32(MIN));
}

Note:- You will always get output an Integer number.

回答4:

After some investigation I wrote this:

import Foundation

struct Math {
   private static var seeded = false

   static func randomFractional() -> CGFloat {

      if !Math.seeded {
         let time = Int(NSDate().timeIntervalSinceReferenceDate)
         srand48(time)
         Math.seeded = true
      }

      return CGFloat(drand48())
   }
}

Now you can just do Math.randomFraction() to get random numbers [0..1[ without having to remember seeding first. Hope this helps someone :o)

回答5:

Another option is to use the xorshift128plus algorithm:

func xorshift128plus(seed0 : UInt64, _ seed1 : UInt64) -> () -> UInt64 {
    var state0 : UInt64 = seed0
    var state1 : UInt64 = seed1
    if state0 == 0 && state1 == 0 {
        state0 = 1 // both state variables cannot be 0
    }

    func rand() -> UInt64 {
        var s1 : UInt64 = state0
        let s0 : UInt64 = state1
        state0 = s0
        s1 ^= s1 << 23
        s1 ^= s1 >> 17
        s1 ^= s0
        s1 ^= s0 >> 26
        state1 = s1
        return UInt64.addWithOverflow(state0, state1).0
    }

    return rand
}

This algorithm has a period of 2^128 - 1 and passes all the tests of the BigCrush test suite. Note that while this is a high-quality pseudo-random number generator with a long period, it is not a cryptographically secure random number generator.

You could seed it from the current time or any other random source of entropy. For example, if you had a function called urand64() that read a UInt64 from /dev/urandom, you could use it like this:

let rand = xorshift128plus(urand64(), urand64())
for _ in 1...10 {
    print(rand())
}

回答6:

Update with swift 4.2 :

let randomInt = Int.random(in: 1..<5)
let randomFloat = Float.random(in: 1..<10)
let randomDouble = Double.random(in: 1...100)
let randomCGFloat = CGFloat.random(in: 1...1000)

回答7:

let MAX : UInt32 = 9
let MIN : UInt32 = 1 
func randomNumber()
{
   var random_number = Int(arc4random_uniform(MAX) + MIN)
   print ("random = ", random_number);    
}

回答8:

In Swift 3 :

It will generate random number between 0 to limit

let limit : UInt32 = 6
print("Random Number : \(arc4random_uniform(limit))")

回答9:

My implementation as an Int extension. Will generate random numbers in range from..<to

public extension Int {
    static func random(from: Int, to: Int) -> Int {
        guard to > from else {
            assertionFailure("Can not generate negative random numbers")
            return 0
        }
        return Int(arc4random_uniform(UInt32(to - from)) + UInt32(from))
    }
}

回答10:

This is how I get a random number between 2 int's!

func randomNumber(MIN: Int, MAX: Int)-> Int{
    var list : [Int] = []
    for i in MIN...MAX {
        list.append(i)
    }
    return list[Int(arc4random_uniform(UInt32(list.count)))]
}

usage:

print("My Random Number is: \(randomNumber(MIN:-10,MAX:10))")

回答11:

you can use this in specific rate:

let die = [1, 2, 3, 4, 5, 6]
 let firstRoll = die[Int(arc4random_uniform(UInt32(die.count)))]
 let secondRoll = die[Int(arc4random_uniform(UInt32(die.count)))]

回答12:

Lets Code with Swift for the random number or random string :)

let quotes: NSArray = ["R", "A", "N", "D", "O", "M"]

      let randomNumber = arc4random_uniform(UInt32(quotes.count))
      let quoteString = quotes[Int(randomNumber)]
      print(quoteString)

it will give you output randomly.

回答13:

Don't forget that some numbers will repeat! so you need to do something like....

my totalQuestions was 47.

func getRandomNumbers(totalQuestions:Int) -> NSMutableArray
{

    var arrayOfRandomQuestions: [Int] = []

    print("arraySizeRequired = 40")
    print("totalQuestions = \(totalQuestions)")

    //This will output a 40 random numbers between 0 and totalQuestions (47)
    while arrayOfRandomQuestions.count < 40
    {

        let limit: UInt32 = UInt32(totalQuestions)

        let theRandomNumber = (Int(arc4random_uniform(limit)))

            if arrayOfRandomQuestions.contains(theRandomNumber)
            {
                print("ping")

            }
            else
            {
            //item not found
                arrayOfRandomQuestions.append(theRandomNumber)
            }

    }

    print("Random Number set = \(arrayOfRandomQuestions)")
    print("arrayOutputCount = \(arrayOfRandomQuestions.count)")


    return arrayOfRandomQuestions as! NSMutableArray

}

回答14:

Another option is to use GKMersenneTwisterRandomSource from GameKit. The docs say:

A deterministic pseudo-random source that generates random numbers based on a mersenne twister algorithm. This is a deterministic random source suitable for creating reliable gameplay mechanics. It is slightly slower than an Arc4 source, but more random, in that it has a longer period until repeating sequences. While deterministic, this is not a cryptographic random source. It is however suitable for obfuscation of gameplay data.

import GameKit

let minValue = 0
let maxValue = 100

var randomDistribution: GKRandomDistribution?
let randomSource = GKMersenneTwisterRandomSource()
randomDistribution = GKRandomDistribution(randomSource: randomSource, lowestValue: minValue, highestValue: maxValue)
let number = randomDistribution?.nextInt() ?? 0
print(number)

Example taken from Apple's sample code: https://github.com/carekit-apple/CareKit/blob/master/CareKitPrototypingTool/OCKPrototyper/CareKitPatient/RandomNumberGeneratorHelper.swift

回答15:

I'm late to the party 🤩🎉

Using a function that allows you to change the size of the array and the range selection on the fly is the most versatile method. You can also use map so it's very concise. I use it in all of my performance testing/bench marking.

elements is the number of items in the array
only including numbers from 0...max

func randArr(_ elements: Int, _ max: Int) -> [Int] {
        return (0..<elements).map{ _ in Int.random(in: 0...max) }
    }

Code Sense / Placeholders look like this. randArr(elements: Int, max: Int)

10 elements in my array ranging from 0 to 1000.

randArr(10, 1000) // [554, 8, 54, 87, 10, 33, 349, 888, 2, 77]

回答16:

look, i had the same problem but i insert the function as a global variable

var RNumber = Int(arc4random_uniform(9)+1)

func GetCase(){

your code
}

obviously this is not efficent, so then i just copy and paste the code into the function so it could be reusable, then xcode suggest me to set the var as constant so my code were

func GetCase() {

let RNumber = Int(arc4random_uniform(9)+1)

   if categoria == 1 {
    }
}

well thats a part of my code so xcode tell me something of inmutable and initialization but, it build the app anyway and that advice simply dissapear

hope it helps

来源：https://stackoverflow.com/questions/32552336/generating-random-numbers-with-swift

标签

swift

arc4random