Question

这是用Swift编写的Eratosthenes筛选器的应用程序。我能够在一个文件上写输出，但我只能通过手动传递[primesList]来开始。相反，我想读取文件primesList.txt并将其放在[primesList]中。

import Foundation

// set a file called test.txt on Desktop to be used by this program
let dir = "~/Desktop"
let file = "primesList.txt"
let path = dir.stringByExpandingTildeInPath
let filePath: NSString = path.stringByAppendingPathComponent(file)

// set some needed variables and constants
var highestNumberEvaluated = 100
var primesList = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]

let readFromFile = String(contentsOfFile: filePath, encoding: NSUTF8StringEncoding, error: nil)
println(readFromFile)

let inputNumber = 100
let range2Evaluate = 100
let last2Evaluate = inputNumber + range2Evaluate

println("Find primes between \(inputNumber) and \(last2Evaluate):\n")

// create a dictionary of numbers to be evaluated true or false
var numbersList = [Int: Bool]()
for i in inputNumber...last2Evaluate {
  numbersList[i] = true
}

// mark as not prime (false) all not primes in numbersList
for i in primesList {
  if i < Int(sqrt(Double(last2Evaluate))) {
    let myMultiplier = inputNumber / i
    var bottomValue = i * myMultiplier
    for var j = bottomValue; j < (bottomValue + range2Evaluate + 2); j += i {
      numbersList[j] = false
    }
  } else {break}
}

// create an array made by all primes found true, then sort
var primesFoundList = [Int]()
for (myKey, myValue) in numbersList {
  if myValue == true {
    primesFoundList.append(myKey)
  }
}
primesFoundList.sort { $0 < $1 }

// add the primes found to the original primes list and write on the file test.txt
primesList += primesFoundList
let toBeWritten = toString(primesList)
toBeWritten.writeToFile(filePath, atomically: true, encoding: NSUTF8StringEncoding, error: nil)

在第13-14行我可以获取文件的内容，如何在数组[primesList]中写这个内容？

Answer 1

toString()函数不太适合生成输出再读一遍。您可以使用

创建一个简单的逗号分隔列表

let toBeWritten = ", ".join(primesList.map { String($0)})
toBeWritten.writeToFile(filePath, atomically: true, encoding: NSUTF8StringEncoding, error: nil)

可以用

再次阅读

if let readFromFile = String(contentsOfFile: filePath, encoding: NSUTF8StringEncoding, error: nil) {
    primesList = readFromFile.componentsSeparatedByString(",").map() { ($0 as NSString).integerValue }
}

（注意：这假定文件格式正确，否则可能会崩溃。）

或者，使用writeToFile()编写的NSArray方法数组作为属性列表（XML）文件：

(primesList as NSArray).writeToFile(filePath, atomically: false)

可以用

回读

if let storedList = NSArray(contentsOfFile: filePath) as? [Int] {
    primesList = storedList
}

如何从文件中读取并放入一个数组

1 个答案: