Read and write a String from text file

I need to read and write data to/from a text file, but I haven't been able to figure out how.

I found this sample code in the Swift's iBook, but I still don't know how to write or read data.

import Cocoa

class DataImporter
{
    /*
    DataImporter is a class to import data from an external file.
    The class is assumed to take a non-trivial amount of time to initialize.
    */
    var fileName = "data.txt"
    // the DataImporter class would provide data importing functionality here
}

class DataManager
{
    @lazy var importer = DataImporter()
    var data = String[]()
    // the DataManager class would provide data management functionality here
}

let manager = DataManager()
manager.data += "Some data"
manager.data += "Some more data"
// the DataImporter instance for the importer property has not yet been created”

println(manager.importer.fileName)
// the DataImporter instance for the importer property has now been created
// prints "data.txt”



var str = "Hello World in Swift Language."

Solution 1:

For reading and writing you should use a location that is writeable, for example documents directory. The following code shows how to read and write a simple string. You can test it on a playground.

Swift 3.x - 5.x

let file = "file.txt" //this is the file. we will write to and read from it

let text = "some text" //just a text

if let dir = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first {

    let fileURL = dir.appendingPathComponent(file)

    //writing
    do {
        try text.write(to: fileURL, atomically: false, encoding: .utf8)
    }
    catch {/* error handling here */}

    //reading
    do {
        let text2 = try String(contentsOf: fileURL, encoding: .utf8)
    }
    catch {/* error handling here */}
}

Swift 2.2

let file = "file.txt" //this is the file. we will write to and read from it

let text = "some text" //just a text

if let dir = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.AllDomainsMask, true).first {
    let path = NSURL(fileURLWithPath: dir).URLByAppendingPathComponent(file)

    //writing
    do {
        try text.writeToURL(path, atomically: false, encoding: NSUTF8StringEncoding)
    }
    catch {/* error handling here */}

    //reading
    do {
        let text2 = try NSString(contentsOfURL: path, encoding: NSUTF8StringEncoding)
    }
    catch {/* error handling here */}
}

Swift 1.x

let file = "file.txt"

if let dirs : [String] = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.AllDomainsMask, true) as? [String] {
    let dir = dirs[0] //documents directory
    let path = dir.stringByAppendingPathComponent(file);
    let text = "some text"

    //writing
    text.writeToFile(path, atomically: false, encoding: NSUTF8StringEncoding, error: nil);

    //reading
    let text2 = String(contentsOfFile: path, encoding: NSUTF8StringEncoding, error: nil)
}

Solution 2:

Assuming that you have moved your text file data.txt to your Xcode-project (Use drag'n'drop and check "Copy files if necessary") you can do the following just like in Objective-C:

let bundle = NSBundle.mainBundle()
let path = bundle.pathForResource("data", ofType: "txt")        
let content = NSString.stringWithContentsOfFile(path) as String

println(content) // prints the content of data.txt

Update:
For reading a file from Bundle (iOS) you can use:

let path = NSBundle.mainBundle().pathForResource("FileName", ofType: "txt")
var text = String(contentsOfFile: path!, encoding: NSUTF8StringEncoding, error: nil)!
println(text)

Update for Swift 3:

let path = Bundle.main.path(forResource: "data", ofType: "txt") // file path for file "data.txt"
var text = String(contentsOfFile: path!, encoding: NSUTF8StringEncoding, error: nil)!

For Swift 5

let path = Bundle.main.path(forResource: "ListAlertJson", ofType: "txt") // file path for file "data.txt"
let string = try String(contentsOfFile: path!, encoding: String.Encoding.utf8)

Solution 3:

Xcode 8.x • Swift 3.x or later

do {
    // get the documents folder url
    if let documentDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first {
        // create the destination url for the text file to be saved
        let fileURL = documentDirectory.appendingPathComponent("file.txt")
        // define the string/text to be saved
        let text = "Hello World !!!"
        // writing to disk 
        // Note: if you set atomically to true it will overwrite the file if it exists without a warning
        try text.write(to: fileURL, atomically: false, encoding: .utf8)
        print("saving was successful")
        // any posterior code goes here
        // reading from disk
        let savedText = try String(contentsOf: fileURL)
        print("savedText:", savedText)   // "Hello World !!!\n"
    }
} catch {
    print("error:", error)
}