linuxreadwrite.swift

import Glibc

// Swift 3 version here: https://gist.github.com/erica/7aee99db9753a1636e0fbed8d68b5845

/*
   Did a bunch of tweaks this morning: 
      removed == true (sorry Kametrixom!)
      cleaned up both stringFromBytes and bytesFromString
      changed fperror check to guard
      replaced use of 1024 in several places with a single constant
*/


// Convert String to UInt8 bytes
func bytesFromString(string: String) -> [UInt8] {
    return Array(string.utf8)
}

// Convert UInt8 bytes to String
func stringFromBytes(bytes: UnsafeMutablePointer<UInt8>, count: Int) -> String {
    return String((0..<count).map ({Character(UnicodeScalar(bytes[$0]))}))
}

// Use fopen/fwrite to output string
func writeStringToFile(string: String, path: String) -> Bool {
    let fp = fopen(path, "w"); defer {fclose(fp)}
    let byteArray = bytesFromString(string)
    let count = fwrite(byteArray, 1, byteArray.count, fp)
    return count == string.utf8.count
}

// Use fread to input string
func readStringFromFile(path: String) -> String {
    let fp = fopen(path, "r"); defer {fclose(fp)}
    var outputString = ""
    let chunkSize = 1024
    let buffer: UnsafeMutablePointer<UInt8> = UnsafeMutablePointer.alloc(chunkSize); defer {buffer.dealloc(chunkSize)}
    repeat {
        let count: Int = fread(buffer, 1, chunkSize, fp)
        guard ferror(fp) == 0 else {break}
        if count > 0 {
            outputString += stringFromBytes(buffer, count: count)
        }
    } while feof(fp) == 0

    return outputString
}

// Simple test case writes to file and reads back in
let inputString = "Hello Sailor"
let path = "/tmp/test.txt"
if writeStringToFile(inputString, path: path) {
    let outputString = readStringFromFile(path)
    print("String:", outputString)
}