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

You can also let Swift do it for you!

import Foundation

// Example function:
func printUTF8Vals(_ ptr: UnsafePointer<UInt8>, _ len: Int) { 
    for i in 0..<len { 
        print(ptr[i]) 
    } 
} 

// Call it:
let str = "Hello"
printUTF8Vals(str, str.lengthOfBytes(using: String.Encoding.utf8))

// Prints:
// 72
// 101
// 108
// 108
// 111

Answer 2

An answer for people working in Swift 4 now. You can no longer get bytes from a Data object, you have to copy them into an UnsafeMutablePointer

let helloWorld = "Hello World!"

let data = helloWorld.data(using: String.Encoding.utf8, allowLossyConversion: false)!
var dataMutablePointer = UnsafeMutablePointer<UInt8>.allocate(capacity: data.count)

//Copies the bytes to the Mutable Pointer
data.copyBytes(to: dataMutablePointer, count: data.count)

//Cast to regular UnsafePointer
let dataPointer = UnsafePointer<UInt8>(dataMutablePointer)

//Your stream
oStream.write(dataPointer, maxLength: data.count)

Answer 3

By far the easiest way (in Swift 5):

let s = "hello, world"
let pointer = UnsafePointer(Array(s.utf8CString))

Not sure how backwards compatible this is.