String of Binary Values to Binary File

Question

I have a large string (~600 bytes) of binary bits that I need to save into a binary file.

If I just save the string to a file using String.write then the 1's and 0's will be encoded as their Unicode/ASCII values.

I need it so that if I opened the file with xxd -b for example it would output the same binary bits as I currently have in the string.

How can I accomplish this?

Why do you use a string (of "0" and "1" characters) for the bits, and not a more appropriate data structure, like Data? — Martin R
– Martin R, Commented Jun 21, 2020 at 15:30

Rob · Accepted Answer · 2020-06-21 19:29:13Z

1

If you have a string with a series of “0” and “1” characters, and want a binary representation, you can do:

extension String {
    var binaryData: Data {
        let values = try! NSRegularExpression(pattern: "[01]{8}")
            .matches(in: self, range: NSRange(startIndex..., in: self))
            .compactMap { Range($0.range, in: self) }
            .compactMap { self[$0] }
            .compactMap { UInt8($0, radix: 2) }
        return Data(values)
    }
}

Thus

let input = "010000010100001001000011"
let data = input.binaryData               // 0x41 0x42 0x43

You can then write that Data to a file, or do whatever you want with it.

answered Jun 21, 2020 at 19:29

Rob

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