Swift. Get binary string from an integer

Question

I have binary 0000010 which is represented as an array of ints. From this binary I get an Integer:

let number = Int32([0, 0, 0, 0, 0, 1, 0].reduce(0, combine: {$0*2 + $1})) // number = 2

but when I want to inverse operation to get a String:

let binaryString = String(2, radix: 2) // binaryString = "10"

So seems radix cuts some bits if they are 0, how to return 5 more zeros?

Do you really want a string, or do you want an array back? — Martin R
– Martin R, Commented Sep 14, 2016 at 12:14

Mehdi Mirzaei · Accepted Answer · 2016-09-14 18:03:46Z

3

let binaryString = String(2, radix: 2)
let other = String(count: 8 - binaryString.characters.count, repeatedValue: Character("0")) + binaryString

answered Sep 14, 2016 at 18:03

Mehdi Mirzaei

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1 Comment

J. Chomel Over a year ago

While this code snippet may solve the question, including an explanation really helps to improve the quality of your post. Remember that you are answering the question for readers in the future, and those people might not know the reasons for your code suggestion.

Dejan Skledar · Accepted Answer · 2016-09-14 11:48:19Z

3

The String constructor can't know how many zero bits the Integer had before the conversion. You'll have to handle that yourself.

By the way, Int also has the radix constructor, for converting strings into Int:

Int("0000010", radix: 2) // Returns 2

answered Sep 14, 2016 at 11:48

Dejan Skledar

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2 Comments

user2924482 Over a year ago

Can you please explain why of radix: 2 I mean 2?

Dejan Skledar Over a year ago

@user2924482 Radix is the number base, in this case 2 means binary. en.wikipedia.org/wiki/Radix

Carlos Guzman · Accepted Answer · 2022-04-26 11:44:49Z

0

Swift 5

var binaryString = String(2, radix: 2)
binaryString = String(repeating: "0", count: 8 - binaryString.count) + binaryString

edited Apr 26, 2022 at 11:44

answered Apr 26, 2022 at 2:00

Carlos Guzman

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Comments

kafran · Accepted Answer · 2022-11-16 11:43:14Z

The documentation for the FixedWidthInteger protocol brings an interesting example for representing the number’s binary:

extension FixedWidthInteger {
    var binaryString: String {
        var result: [String] = []
        for i in 0..<(Self.bitWidth / 8) {
            let byte = UInt8(truncatingIfNeeded: self >> (i * 8))
            let byteString = String(byte, radix: 2)
            let padding = String(repeating: "0",
                                 count: 8 - byteString.count)
            result.append(padding + byteString)
        }
        return "0b" + result.reversed().joined(separator: "_")
    }
}


print(Int16.max.binaryString) // Prints "0b01111111_11111111"
print((101 as UInt8).binaryString) // Prints "0b11001001"

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