swift - How to convert String to UnsafePointer<UInt8> and length

Question

When I using NSOutputStream's write method

func write(_ buffer: UnsafePointer<UInt8>, maxLength length: Int) -> Int

I don't know how to convert String to UnsafePointer<UInt8> and length

How can I do this in swift?

Answer 1

You have to convert the string to UTF-8 data first

let string = "foo bar"
let data = string.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)!

and then write it to the output stream

let outputStream: NSOutputStream = ... // the stream that you want to write to
let bytesWritten = outputStream.write(UnsafePointer(data.bytes), maxLength: data.length)

The UnsafePointer() cast is necessary because data.bytes has the type UnsafePointer<Void>, and not UnsafePointer<UInt8> as expected by the write() method.

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Update for Swift 3:

let string = "foo bar"
// Conversion to UTF-8 data (cannot fail):
let data = string.data(using: String.Encoding.utf8)! 

// Write to output stream:
let outputStream: NSOutputStream = ... // the stream that you want to write to
let bytesWritten = data.withUnsafeBytes { outputStream.write($0, maxLength: data.count) }