How to convert an Int to Hex String in Swift

Question

In Obj-C I used to convert an unsigned integer n to a hex string with

 NSString *st = [NSString stringWithFormat:@\"%2X\", n];

I tried for

Answer 1

With Swift 5, according to your needs, you may choose one of the three following methods in order to solve your problem.

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#1. Using String's init(_:radix:uppercase:) initializer

Swift String has a init(_:radix:uppercase:) initializer with the following declaration:

init(_ value: T, radix: Int = 10, uppercase: Bool = false) where T : BinaryInteger

Creates a string representing the given value in base 10, or some other specified base.

The Playground code below shows how to create a String instance that represents an integer value in hexadecimal format by using init(_:radix:uppercase:) and without having to import Foundation:

let string1 = String(2, radix: 16)
print(string1) // prints: "2"

let string2 = String(211, radix: 16)
print(string2) // prints: "d3"

let string3 = String(211, radix: 16, uppercase: true)
print(string3) // prints: "D3"

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#2. Using String's init(format:​_:​) initializer

Foundation provides String a init(format:​_:​) initializer. init(format:​_:​) has the following declaration:

init(format: String, _ arguments: CVarArg...)

Returns a String object initialized by using a given format string as a template into which the remaining argument values are substituted.

The Apple's String Programming Guide gives a list of the format specifiers that are supported by String and NSString. Among those format specifiers, %X has the following description:

Unsigned 32-bit integer (unsigned int), printed in hexadecimal using the digits 0–9 and uppercase A–F.

The Playground code below shows how to create a String instance that represents an integer value in hexadecimal format with init(format:​_:​):

import Foundation

let string1 = String(format:"%X", 2)
print(string1) // prints: "2"

let string2 = String(format:"%02X", 1)
print(string2) // prints: "01"

let string3 = String(format:"%02X", 211)
print(string3) // prints: "D3"

let string4 = String(format: "%02X, %02X, %02X", 12, 121, 255)
print(string4) // prints: "0C, 79, FF"

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#3. Using String's init(format:​arguments:​) initializer

Foundation provides String a init(format:​arguments:​) initializer. init(format:​arguments:​) has the following declaration:

init(format: String, arguments: [CVarArg])

Returns a String object initialized by using a given format string as a template into which the remaining argument values are substituted according to the user’s default locale.

The Playground code below shows how to create a String instance that represents an integer value in hexadecimal format with init(format:​arguments:​):

import Foundation

let string1 = String(format:"%X", arguments: [2])
print(string1) // prints: "2"

let string2 = String(format:"%02X", arguments: [1])
print(string2) // prints: "01"

let string3 = String(format:"%02X",  arguments: [211])
print(string3) // prints: "D3"

let string4 = String(format: "%02X, %02X, %02X",  arguments: [12, 121, 255])
print(string4) // prints: "0C, 79, FF"