Swift Hex to String with Data Extensions

In Swift, hex usually rides on Data: parse hex text into bytes, then decode with String(data:encoding:) when the payload is text. The reverse path is Data → hex for logs, BLE, and hashes.

Concepts: hex encoding overview. Quick check: Hex to String.

Data → hex string

import Foundation

extension Data {
    var hexString: String {
        map { String(format: "%02x", $0) }.joined()
    }
}

let data = "Hello".data(using: .utf8)!
print(data.hexString) // 48656c6c6f

Hex string → Data

extension Data {
    init?(hexString: String) {
        let cleaned = hexString
            .replacingOccurrences(of: " ", with: "")
            .replacingOccurrences(of: "0x", with: "")
        guard cleaned.count % 2 == 0 else { return nil }
        var bytes = [UInt8]()
        bytes.reserveCapacity(cleaned.count / 2)
        var index = cleaned.startIndex
        while index < cleaned.endIndex {
            let next = cleaned.index(index, offsetBy: 2)
            let byteStr = cleaned[index..<next]
            guard let byte = UInt8(byteStr, radix: 16) else { return nil }
            bytes.append(byte)
            index = next
        }
        self.init(bytes)
    }
}

if let data = Data(hexString: "e4bda0e5a5bd"),
   let text = String(data: data, encoding: .utf8) {
    print(text) // 你好
}

Hex → String helper

func string(fromHex hex: String, encoding: String.Encoding = .utf8) -> String? {
    guard let data = Data(hexString: hex) else { return nil }
    return String(data: data, encoding: encoding)
}

Common iOS/macOS uses

• Displaying SHA-256 digests from CryptoKit as hex.
• BLE characteristic values arriving as Data.
• Debugging API payloads that embed binary fields as hex text.

Pitfalls

• Odd-length hex → fail (nil), do not invent padding.
• Wrong String.Encoding → nil or mojibake; prefer .utf8 unless a protocol says otherwise.
• Not every Data is text — keep binary as Data when it is a key, nonce, or file blob.

Related: JavaScript · Python · String to Hex tool.