How to Generate a Random Unicode Character in Swift

How can I generate a random unicode character in Swift?

Unicode Scalar Value

Any Unicode code point except high-surrogate and low-surrogate code
points. In other words, the ranges of integers 0 to D7FF and E000
to 10FFFF inclusive.

So, I've made a small code's snippet. See below.

This code works

func randomUnicodeCharacter() -> String {
    let i = arc4random_uniform(1114111)
    return (i > 55295 && i < 57344) ? randomUnicodeCharacter() : String(UnicodeScalar(i))
}
randomUnicodeCharacter()

This code doesn't work!

let N: UInt32 = 65536
let i = arc4random_uniform(N)
var c = String(UnicodeScalar(i))
print(c, appendNewline: false)

I was a little bit confused with this and this. [Maximum value: 65535]

How to get random element from CharacterSet in Swift

A CharacterSet is not a Collection. It is a SetAlgebra.

It is not, despite its name, "a Set of Characters." It is a "set" of UnicodeScalars (not Characters) in the mathematical sense: a list of rules that define whether a given UnicodeScalar is contained. There is no direct way to enumerate the values. There are inefficient ways to generate a complete list since UnicodeScalar is over a finite range, but it's quite massive.

I'm curious how you would use this, though. This may include a lot of characters you're not expecting like UNDERTIE (‿), SAMARITAN PUNCTUATION BAU (࠳), and THAI CHARACTER FONGMAN (๏). Are you really looking to pick a random value out all Unicode alphanumerics and punctuation? (There are over 800 punctuation characters, for example, and by my rough count maybe 25k alphanumerics. I haven't counted symbols yet, but there are a lot of them. The chance that you'll get a character on a US keyboard is pretty close to zero.)

I expect this is the code you're really looking for:

let asciiRange = 33...126
let randomCharacter = asciiRange.randomElement()
    .flatMap(UnicodeScalar.init)
    .flatMap(Character.init)!

This will return a random, printable ASCII character.

Given that your set is such a large proportion of the Unicode space, the following is how you would get a truly random one reasonably quickly:

func randomCharacter() -> Character {
    // Drops the control characters and SPACE, the private use areas, tags, and the variation selectors.
    // The full range is 0x00...0x10FFFD
    let unicodeRange = 0x21...0x2FA1D
    let validCharacters: CharacterSet = .alphanumerics.union(.punctuationCharacters).union(.symbols)

    repeat {
        if let c = unicodeRange.randomElement().flatMap(UnicodeScalar.init),
           validCharacters.contains(c) {
            return Character(c)
        }
    } while true
}

I just keeps guessing until it finds one. This will tend to converge as long as the set you're picking from is similar in size to the full set. This is likely more efficient than generating a massive Set<Character> which you could do by walking a similar space.

Generate random alphanumeric string in Swift

Swift 4.2 Update

Swift 4.2 introduced major improvements in dealing with random values and elements. You can read more about those improvements here. Here is the method reduced to a few lines:

func randomString(length: Int) -> String {
  let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
  return String((0..<length).map{ _ in letters.randomElement()! })
}

Swift 3.0 Update

func randomString(length: Int) -> String {

    let letters : NSString = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
    let len = UInt32(letters.length)

    var randomString = ""

    for _ in 0 ..< length {
        let rand = arc4random_uniform(len)
        var nextChar = letters.character(at: Int(rand))
        randomString += NSString(characters: &nextChar, length: 1) as String
    }

    return randomString
}

Original answer:

func randomStringWithLength (len : Int) -> NSString {

    let letters : NSString = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"

    var randomString : NSMutableString = NSMutableString(capacity: len)

    for (var i=0; i < len; i++){
        var length = UInt32 (letters.length)
        var rand = arc4random_uniform(length)
        randomString.appendFormat("%C", letters.characterAtIndex(Int(rand)))
    }

    return randomString
}

Working with Unicode code points in Swift

Updated for Swift 3

String and Character

For almost everyone in the future who visits this question, String and Character will be the answer for you.

Set Unicode values directly in code:

var str: String = "I want to visit 北京, Москва, मुंबई, القاهرة, and 서울시. quot;
var character: Character = "quot;

Use hexadecimal to set values

var str: String = "\u{61}\u{5927}\u{1F34E}\u{3C0}" // a大π
var character: Character = "\u{65}\u{301}" // é = "e" + accent mark

Note that the Swift Character can be composed of multiple Unicode code points, but appears to be a single character. This is called an Extended Grapheme Cluster.

See this question also.

Convert to Unicode values:

str.utf8
str.utf16
str.unicodeScalars // UTF-32

String(character).utf8
String(character).utf16
String(character).unicodeScalars

Convert from Unicode hex values:

let hexValue: UInt32 = 0x1F34E

// convert hex value to UnicodeScalar
guard let scalarValue = UnicodeScalar(hexValue) else {
    // early exit if hex does not form a valid unicode value
    return
}

// convert UnicodeScalar to String
let myString = String(scalarValue) // br>

Or alternatively:

let hexValue: UInt32 = 0x1F34E
if let scalarValue = UnicodeScalar(hexValue) {
    let myString = String(scalarValue)
}

A few more examples

let value0: UInt8 = 0x61
let value1: UInt16 = 0x5927
let value2: UInt32 = 0x1F34E

let string0 = String(UnicodeScalar(value0)) // a
let string1 = String(UnicodeScalar(value1)) // 大
let string2 = String(UnicodeScalar(value2)) // br>
// convert hex array to String
let myHexArray = [0x43, 0x61, 0x74, 0x203C, 0x1F431] // an Int array
var myString = ""
for hexValue in myHexArray {
    myString.append(UnicodeScalar(hexValue))
}
print(myString) // Cat‼br>

Note that for UTF-8 and UTF-16 the conversion is not always this easy. (See UTF-8, UTF-16, and UTF-32 questions.)

NSString and unichar

It is also possible to work with NSString and unichar in Swift, but you should realize that unless you are familiar with Objective C and good at converting the syntax to Swift, it will be difficult to find good documentation.

Also, unichar is a UInt16 array and as mentioned above the conversion from UInt16 to Unicode scalar values is not always easy (i.e., converting surrogate pairs for things like emoji and other characters in the upper code planes).

Custom string structure

For the reasons mentioned in the question, I ended up not using any of the above methods. Instead I wrote my own string structure, which was basically an array of UInt32 to hold Unicode scalar values.

Again, this is not the solution for most people. First consider using extensions if you only need to extend the functionality of String or Character a little.

But if you really need to work exclusively with Unicode scalar values, you could write a custom struct.

The advantages are:

• Don't need to constantly switch between Types (String, Character, UnicodeScalar, UInt32, etc.) when doing string manipulation.
• After Unicode manipulation is finished, the final conversion to String is easy.
• Easy to add more methods when they are needed
• Simplifies converting code from Java or other languages

Disadavantages are:

• makes code less portable and less readable for other Swift developers
• not as well tested and optimized as the native Swift types
• it is yet another file that has to be included in a project every time you need it

You can make your own, but here is mine for reference. The hardest part was making it Hashable.

// This struct is an array of UInt32 to hold Unicode scalar values
// Version 3.4.0 (Swift 3 update)

struct ScalarString: Sequence, Hashable, CustomStringConvertible {
    
    fileprivate var scalarArray: [UInt32] = []
    
    
    init() {
        // does anything need to go here?
    }
    
    init(_ character: UInt32) {
        self.scalarArray.append(character)
    }
    
    init(_ charArray: [UInt32]) {
        for c in charArray {
            self.scalarArray.append(c)
        }
    }
    
    init(_ string: String) {
        
        for s in string.unicodeScalars {
            self.scalarArray.append(s.value)
        }
    }
    
    // Generator in order to conform to SequenceType protocol
    // (to allow users to iterate as in `for myScalarValue in myScalarString` { ... })
    func makeIterator() -> AnyIterator<UInt32> {
        return AnyIterator(scalarArray.makeIterator())
    }
    
    // append
    mutating func append(_ scalar: UInt32) {
        self.scalarArray.append(scalar)
    }
    
    mutating func append(_ scalarString: ScalarString) {
        for scalar in scalarString {
            self.scalarArray.append(scalar)
        }
    }
    
    mutating func append(_ string: String) {
        for s in string.unicodeScalars {
            self.scalarArray.append(s.value)
        }
    }
    
    // charAt
    func charAt(_ index: Int) -> UInt32 {
        return self.scalarArray[index]
    }
    
    // clear
    mutating func clear() {
        self.scalarArray.removeAll(keepingCapacity: true)
    }
    
    // contains
    func contains(_ character: UInt32) -> Bool {
        for scalar in self.scalarArray {
            if scalar == character {
                return true
            }
        }
        return false
    }
    
    // description (to implement Printable protocol)
    var description: String {
        return self.toString()
    }
    
    // endsWith
    func endsWith() -> UInt32? {
        return self.scalarArray.last
    }
    
    // indexOf
    // returns first index of scalar string match
    func indexOf(_ string: ScalarString) -> Int? {
        
        if scalarArray.count < string.length {
            return nil
        }
        
        for i in 0...(scalarArray.count - string.length) {
            
            for j in 0..<string.length {
                
                if string.charAt(j) != scalarArray[i + j] {
                    break // substring mismatch
                }
                if j == string.length - 1 {
                    return i
                }
            }
        }
        
        return nil
    }
    
    // insert
    mutating func insert(_ scalar: UInt32, atIndex index: Int) {
        self.scalarArray.insert(scalar, at: index)
    }
    mutating func insert(_ string: ScalarString, atIndex index: Int) {
        var newIndex = index
        for scalar in string {
            self.scalarArray.insert(scalar, at: newIndex)
            newIndex += 1
        }
    }
    mutating func insert(_ string: String, atIndex index: Int) {
        var newIndex = index
        for scalar in string.unicodeScalars {
            self.scalarArray.insert(scalar.value, at: newIndex)
            newIndex += 1
        }
    }
    
    // isEmpty
    var isEmpty: Bool {
        return self.scalarArray.count == 0
    }
    
    // hashValue (to implement Hashable protocol)
    var hashValue: Int {
        
        // DJB Hash Function
        return self.scalarArray.reduce(5381) {
            ($0 << 5) &+ $0 &+ Int($1)
        }
    }
    
    // length
    var length: Int {
        return self.scalarArray.count
    }
    
    // remove character
    mutating func removeCharAt(_ index: Int) {
        self.scalarArray.remove(at: index)
    }
    func removingAllInstancesOfChar(_ character: UInt32) -> ScalarString {
        
        var returnString = ScalarString()
        
        for scalar in self.scalarArray {
            if scalar != character {
                returnString.append(scalar)
            }
        }
        
        return returnString
    }
    func removeRange(_ range: CountableRange<Int>) -> ScalarString? {
        
        if range.lowerBound < 0 || range.upperBound > scalarArray.count {
            return nil
        }
        
        var returnString = ScalarString()
        
        for i in 0..<scalarArray.count {
            if i < range.lowerBound || i >= range.upperBound {
                returnString.append(scalarArray[i])
            }
        }
        
        return returnString
    }
    
    
    // replace
    func replace(_ character: UInt32, withChar replacementChar: UInt32) -> ScalarString {
        
        var returnString = ScalarString()
        
        for scalar in self.scalarArray {
            if scalar == character {
                returnString.append(replacementChar)
            } else {
                returnString.append(scalar)
            }
        }
        return returnString
    }
    func replace(_ character: UInt32, withString replacementString: String) -> ScalarString {
        
        var returnString = ScalarString()
        
        for scalar in self.scalarArray {
            if scalar == character {
                returnString.append(replacementString)
            } else {
                returnString.append(scalar)
            }
        }
        return returnString
    }
    func replaceRange(_ range: CountableRange<Int>, withString replacementString: ScalarString) -> ScalarString {
        
        var returnString = ScalarString()
        
        for i in 0..<scalarArray.count {
            if i < range.lowerBound || i >= range.upperBound {
                returnString.append(scalarArray[i])
            } else if i == range.lowerBound {
                returnString.append(replacementString)
            }
        }
        return returnString
    }
    
    // set (an alternative to myScalarString = "some string")
    mutating func set(_ string: String) {
        self.scalarArray.removeAll(keepingCapacity: false)
        for s in string.unicodeScalars {
            self.scalarArray.append(s.value)
        }
    }
    
    // split
    func split(atChar splitChar: UInt32) -> [ScalarString] {
        var partsArray: [ScalarString] = []
        if self.scalarArray.count == 0 {
            return partsArray
        }
        var part: ScalarString = ScalarString()
        for scalar in self.scalarArray {
            if scalar == splitChar {
                partsArray.append(part)
                part = ScalarString()
            } else {
                part.append(scalar)
            }
        }
        partsArray.append(part)
        return partsArray
    }
    
    // startsWith
    func startsWith() -> UInt32? {
        return self.scalarArray.first
    }
    
    // substring
    func substring(_ startIndex: Int) -> ScalarString {
        // from startIndex to end of string
        var subArray: ScalarString = ScalarString()
        for i in startIndex..<self.length {
            subArray.append(self.scalarArray[i])
        }
        return subArray
    }
    func substring(_ startIndex: Int, _ endIndex: Int) -> ScalarString {
        // (startIndex is inclusive, endIndex is exclusive)
        var subArray: ScalarString = ScalarString()
        for i in startIndex..<endIndex {
            subArray.append(self.scalarArray[i])
        }
        return subArray
    }
    
    // toString
    func toString() -> String {
        var string: String = ""
        
        for scalar in self.scalarArray {
            if let validScalor = UnicodeScalar(scalar) {
                string.append(Character(validScalor))
            }
        }
        return string
    }
    
    // trim
    // removes leading and trailing whitespace (space, tab, newline)
    func trim() -> ScalarString {
        
        //var returnString = ScalarString()
        let space: UInt32 = 0x00000020
        let tab: UInt32 = 0x00000009
        let newline: UInt32 = 0x0000000A
        
        var startIndex = self.scalarArray.count
        var endIndex = 0
        
        // leading whitespace
        for i in 0..<self.scalarArray.count {
            if self.scalarArray[i] != space &&
                self.scalarArray[i] != tab &&
                self.scalarArray[i] != newline {
                
                startIndex = i
                break
            }
        }
        
        // trailing whitespace
        for i in stride(from: (self.scalarArray.count - 1), through: 0, by: -1) {
            if self.scalarArray[i] != space &&
                self.scalarArray[i] != tab &&
                self.scalarArray[i] != newline {
                
                endIndex = i + 1
                break
            }
        }
        
        if endIndex <= startIndex {
            return ScalarString()
        }
        
        return self.substring(startIndex, endIndex)
    }
    
    // values
    func values() -> [UInt32] {
        return self.scalarArray
    }
    
}

func ==(left: ScalarString, right: ScalarString) -> Bool {
    return left.scalarArray == right.scalarArray
}

func +(left: ScalarString, right: ScalarString) -> ScalarString {
    var returnString = ScalarString()
    for scalar in left.values() {
        returnString.append(scalar)
    }
    for scalar in right.values() {
        returnString.append(scalar)
    }
    return returnString
}

How do I capture unicode character with swift regex

I debugged the strings containing \u{e2} with Xcode with the following code:

snippet.characters.forEach { character in
    print(character)
}

After setting a breakpoint at the print line I found out that although the Xcode debugger shows the following Unicode characters as \u{e2} when looking at the string the characters which I was actually confronted with were

https://unicode-table.com/en/200E/

https://unicode-table.com/en/202A/

https://unicode-table.com/en/202C/

I could capture the unicode characters with the following code with my extension outlined in the question above:

snippet.capturedGroups(forRegex: "([\\u200E]{1})")
snippet.capturedGroups(forRegex: "([\\u202A]{1})")
snippet.capturedGroups(forRegex: "([\\u202C]{1})")

How to express Strings in Swift using Unicode hexadecimal values (UTF-16)

Character

The Swift syntax for forming a hexadecimal code point is

\u{n}

where n is a hexadecimal number up to 8 digits long. The valid range for a Unicode scalar is U+0 to U+D7FF and U+E000 to U+10FFFF inclusive. (The U+D800 to U+DFFF range is for surrogate pairs, which are not scalars themselves, but are used in UTF-16 for encoding the higher value scalars.)

Examples:

// The following forms are equivalent. They all produce "C". 
let char1: Character = "\u{43}"
let char2: Character = "\u{0043}"
let char3: Character = "\u{00000043}"

// Higher value Unicode scalars are done similarly
let char4: Character = "\u{203C}" // ‼ (DOUBLE EXCLAMATION MARK character)
let char5: Character = "\u{1F431}" // (cat emoji)

// Characters can be made up of multiple scalars
let char7: Character = "\u{65}\u{301}" // é = "e" + accent mark
let char8: Character = "\u{65}\u{301}\u{20DD}" // é⃝ = "e" + accent mark + circle

Notes:

• Leading zeros can be added or omitted
• Characters are known as extended grapheme clusters. Even when they are composed of multiple scalars, they are still considered a single character. What is key is that they appear to be a single character (grapheme) to the user.
• TODO: How to convert surrogate pair to Unicode scalar in Swift

String

Strings are composed of characters. See the following examples for some ways to form them using hexadecimal code points.

Examples:

var string1 = "\u{0043}\u{0061}\u{0074}\u{203C}\u{1F431}" // Cat‼br>
// pass an array of characters to a String initializer
let catCharacters: [Character] = ["\u{0043}", "\u{0061}", "\u{0074}", "\u{203C}", "\u{1F431}"] // ["C", "a", "t", "‼", "quot;]
let string2 = String(catCharacters) // Cat‼br>

Converting Hex Values at Runtime

At runtime you can convert hexadecimal or Int values into a Character or String by first converting it to a UnicodeScalar.

Examples:

// hex values
let value0: UInt8  = 0x43     // 67
let value1: UInt16 = 0x203C   // 8252
let value2: UInt32 = 0x1F431  // 128049

// convert hex to UnicodeScalar
let scalar0 = UnicodeScalar(value0)
// make sure that UInt16 and UInt32 form valid Unicode values
guard
    let scalar1 = UnicodeScalar(value1),
    let scalar2 = UnicodeScalar(value2) else {
    return
}

// convert to Character
let character0 = Character(scalar0) // C
let character1 = Character(scalar1) // ‼
let character2 = Character(scalar2) // br>
// convert to String
let string0 = String(scalar0) // C
let string1 = String(scalar1) // ‼
let string2 = String(scalar2) // br>
// convert hex array to String
let myHexArray = [0x43, 0x61, 0x74, 0x203C, 0x1F431] // an Int array
var myString = ""
for hexValue in myHexArray {
    if let scalar = UnicodeScalar(hexValue) {
        myString.append(Character(scalar))
    }
}
print(myString) // Cat‼br>

Further reading

• Strings and Characters docs
• Glossary of Unicode Terms
• Strings in Swift
• Working with Unicode code points in Swift

How to convert Unicode Character to Int in Swift

Hex to Int

If you are starting with \u{0D85} and you know the hex value of the Unicode character, then you might as well write it in the following format because it is an Int already.

let myInt = 0x0D85                          // Int: 3461

String to Int

I assume, though, that you have "\u{0D85}" (in quotes), which makes it a String by default. And since it is a String, you can't be certain that you will only have a single Int value for the general case.

let myString = "\u{0D85}"

for element in myString.unicodeScalars {
    let myInt = element.value               // UInt32: 3461
}

I could have also used myString.utf16 and let myInt = Int(element), but I find it easier to deal with Unicode scalar values (UTF-32) when there is a possibility of things like emoji. (See this answer for more details.)

Character to Int

Swift Character, which is an extended grapheme cluster, does not have a utf16 or unicodeScalars property, so if you are starting with Character then convert it to a String first and then follow the directions in the String to Int section above.

let myChar: Character = "\u{0D85}"
let myString = String(myChar)

How to get a random unicode character in objective C

If you truly want a random character, something like

UniChar uc = arc4random() % (0xffffu + 1);        
CTFontGetGlyphsForCharacters((CTFontRef)arialUnicode, &uc, (CGGlyph *)glyphs, 1);

But depending on what you are trying to do

• There are much easier ways to display text in Cocoa, particularly NSTextField
• There are so many characters in Unicode it's highly unlikely a single font will contain all the glyphs.

Do you really want a random unicode code point or do you want to select from a subset of the available characters? See http://www.unicode.org/charts/ to get an idea of just how much Unicode covers.

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