【Swift】 文字コードの変換 を整理してみた 👉 https://android.benigumo.com/20240611/encoding/

convert_encoding.swift

// with: 
// FileManageExtensions.swift 
// https://gist.github.com/benigumocom/6a8e4506438b5260469c12b1c12c0fb7

do {
  let documents = URL.documentsDirectory
  let text = "あいうえお"

  // convert to data bytes
  print(
    text.data(using: .shiftJIS)!,
    text.data(using: .shiftJIS)!.map { String(format: "%02X", $0) }.joined()
  ) 
  print(
    text.data(using: .utf8)!,
    text.data(using: .utf8)!.map { String(format: "%02X", $0) }.joined()
  )
  // 10 bytes 82A082A282A482A682A8
  // 15 bytes E38182E38184E38186E38188E3818A

  print()

  fileManager.showContents()
  print()
  // /HOME/Documents/

  // create source file
  let source = documents.appending(component: "sourceS.txt")
  try! text.write(to: source, atomically: true, encoding: .shiftJIS)

  fileManager.showContents()
  print()
  // /HOME/Documents/
  // /HOME/Documents/sourceS.txt [10 bytes]

  // file to Data
  let data = try! Data(contentsOf: source)
  print(data) // 10 bytes ← Shift_JIS
  print()

  // remove source file
  try! fileManager.removeItem(at: source)
  fileManager.showContents()
  print()
  // /HOME/Documents/

  // Data to String
  let string = String(data: data, encoding: .shiftJIS)! // convert
  print(string) // あいうえお
  print()

  // String to Data
  let dataS = string.data(using: .shiftJIS)!  // convert
  print(dataS) // 10 bytes
  print()

  let dataU = string.data(using: .utf8)!
  print(dataU) // 15 bytes
  print()

  // Data to file
  let fileS = documents.appending(component: "textS.txt")
  let fileU = documents.appending(component: "textU.txt")
  try! dataS.write(to: fileS)
  try! dataU.write(to: fileU)

  fileManager.showContents()
  print()
  // /HOME/Documents/
  // /HOME/Documents/textU.txt [15 bytes]
  // /HOME/Documents/textS.txt [10 bytes]

  // file to String
  let stringS = try String(contentsOf: fileS, encoding: .shiftJIS) // convert
  let stringU = try String(contentsOf: fileU, encoding: .utf8)

  print(stringS, stringU) // あいうえお あいうえお
  print(stringS == stringU)
  print()

  // remove result files
  try fileManager.removeItem(at: fileS)
  try fileManager.removeItem(at: fileU)
  fileManager.showContents()
  print()
  // /HOME/Documents/

  // String to file
  try stringS.write(to: fileS, atomically: true, encoding: .shiftJIS) // convert
  try stringU.write(to: fileU, atomically: true, encoding: .utf8)
  fileManager.showContents()
  print()
  // /HOME/Documents/
  // /HOME/Documents/textU.txt [15 bytes]
  // /HOME/Documents/textS.txt [10 bytes]

  // remove result files
  try fileManager.removeItem(at: fileS)
  try fileManager.removeItem(at: fileU)
  fileManager.showContents()
  print()
  // /HOME/Documents/

} catch {
  print(error.localizedDescription)
}