Swift native functions to have numbers as hex strings

As of Swift 2, all integer types have a constructor

init?(_ text: String, radix: Int = default)

so that both integerto hex string and hex string to integer conversions can be donewith built-in methods. Example:

let num = 1000let str = String(num, radix: 16)print(str) // "3e8"if let num2 = Int(str, radix: 16) {    print(num2) // 1000}

(Old answer for Swift 1:) The conversion from an integer to a hex string can be done with

let hex = String(num, radix: 16)

(see for example How to convert a decimal number to binary in Swift?). This does not require the import of any Frameworkand works with any base between 2 and 36.

The conversion from a hex string to an integer can be done with the BSDlibrary function strtoul() (compare How to convert a binary to decimal in Swift?) if you are willing to import Darwin.

Otherwise there is (as far as I know) no built-in Swift method. Here is an extensionthat converts a string to a number according to a given base:

extension UInt {    init?(_ string: String, radix: UInt) {        let digits = "0123456789abcdefghijklmnopqrstuvwxyz"        var result = UInt(0)        for digit in string.lowercaseString {            if let range = digits.rangeOfString(String(digit)) {                let val = UInt(distance(digits.startIndex, range.startIndex))                if val >= radix {                    return nil                }                result = result * radix + val            } else {                return nil            }        }        self = result    }}

Example:

let hexString = "A0"if let num = UInt(hexString, radix: 16) {    println(num)} else {    println("invalid input")}

update: Xcode 12.5 • Swift 5.4

extension StringProtocol {    func dropping<S: StringProtocol>(prefix: S) -> SubSequence { hasPrefix(prefix) ? dropFirst(prefix.count) : self[...] }    var hexaToDecimal: Int { Int(dropping(prefix: "0x"), radix: 16) ?? 0 }    var hexaToBinary: String { .init(hexaToDecimal, radix: 2) }    var decimalToHexa: String { .init(Int(self) ?? 0, radix: 16) }    var decimalToBinary: String { .init(Int(self) ?? 0, radix: 2) }    var binaryToDecimal: Int { Int(dropping(prefix: "0b"), radix: 2) ?? 0 }    var binaryToHexa: String { .init(binaryToDecimal, radix: 16) }}

extension BinaryInteger {    var binary: String { .init(self, radix: 2) }    var hexa: String { .init(self, radix: 16) }}

Testing:

print("7fffffffffffffff".hexaToDecimal)      // "9223372036854775807" decimal integerprint("0x7fffffffffffffff".hexaToDecimal)    // "9223372036854775807" decimal integerprint("7fffffffffffffff".hexaToBinary) // "111111111111111111111111111111111111111111111111111111111111111" binary (String)print("0x7fffffffffffffff".hexaToBinary) // "111111111111111111111111111111111111111111111111111111111111111"print("255".decimalToHexa)   // "ff"       hexa (String)print("255".decimalToBinary) // "11111111" binary (String)0b11111111print("11111111".binaryToHexa)      // "ff"  hexa (String)print("0b11111111".binaryToHexa)    // "ff"  hexa (String)print("11111111".binaryToDecimal)   // 255 decimal (Int)print("0b11111111".binaryToDecimal) // 255 decimal (Int)print(255.binary) // "11111111" binary (String)print(255.hexa)   // "ff"       hexa (String)

Swift 3:

String to UInt:

let str = "fcd7d7"let number = UInt(str, radix: 16)!print(number)

result: 16570327

UInt to hex String:

let number = UInt(exactly: 16570327)!let str = String(number, radix: 16, uppercase: false)print(str)

result: fcd7d7