Fast?

test.swift

import Darwin

let string = "hello world"
var array = [UInt8]()

string.withCString { ptr in
    print("strlen: \(strlen(ptr))")

    let length = strlen(ptr)
    var currentPtr = ptr
    var i = 0
    while i != length {
        print("pointee: \(currentPtr.pointee), char: \(Unicode.Scalar(Int(currentPtr.pointee))!)")
        array.append(UInt8(currentPtr.pointee))
        currentPtr = currentPtr.successor()
        i += 1
    }
}

print(array)