How to convert String to UnsafePointer and length

Question

When I using NSOutputStream\'s write method

func write(_ buffer: UnsafePointer, maxLength length: Int) -> Int
         


        

Answer 1

I see there are other answers, and an accepted answer, so it seems you've gotten what you need. I came here because I noticed Swift 5's deprecation warnings for withUnsafeMutableBytes et al, and started testing @abdullahselek's answer, but I noticed in Swift 5 (haven't yet verified if it worked in previous versions) that String is convertible to UnsafePointer in-line, so you can use it in place where an UnsafePointer is expected. In case it helps to see another example, here's our old and updated function, posted here:

OLD

let derivationStatus = localDerivedKeyData.withUnsafeMutableBytes { derivedKeyBytes in
  salt.withUnsafeBytes { saltBytes in

    CCKeyDerivationPBKDF(
      CCPBKDFAlgorithm(kCCPBKDF2),
      password,
      passwordData.count,
      saltBytes,
      salt.count,
      algorithm,
      UInt32(rounds),
      derivedKeyBytes,
      derivedKeyData.count
    )
  }
}

NEW

let derivationStatus = localDerivedKeyData.withUnsafeMutableBytes { (outputBytes: UnsafeMutableRawBufferPointer) -> Int32 in
  let status = CCKeyDerivationPBKDF(
    CCPBKDFAlgorithm(kCCPBKDF2),
    password, // a String
    passwordData.count, // just the password String converted to Data
    String(data: salt, encoding: .utf8),  // converts salt (Data) to String
    salt.count,
    algorithm,
    UInt32(rounds),
    outputBytes.baseAddress?.assumingMemoryBound(to: UInt8.self),
    derivedKeyData.count
  )
  return status
}

With that said, you could use a similar approach to get your stream as follows:

let stream = OutputStream(toBuffer: UnsafeMutablePointer(mutating: someString), capacity: someString.data(using: .utf8)!.count)

(the ! is used to silence the compiler error, but you should avoid force-unwrapping where possible).