Programming Fundamentals/Files/Swift

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strings.swift[edit]

// This program creates a file, adds data to the file, displays the file,
// appends more data to the file, displays the file, and then deletes the file.
// It will not run if the file already exists.
//
// References:
//     https://www.mathsisfun.com/temperature-conversion.html
//     https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/TheBasics.html

import Foundation

func fileExists(filename:String) -> Bool {
    let fileManager = FileManager.default
    return fileManager.fileExists(atPath:filename)
}

func calculateFahrenheit(celsius:Double) -> Double {
    var fahrenheit: Double
    fahrenheit = celsius * 9 / 5 + 32    
    return fahrenheit
}

func createFile(filename:String) {
    var text: String
    var fahrenheit: Double

    text = "C,F\n"
    for celsius in stride(from: 0.0, through: 50.0, by: 1.0) {
        fahrenheit = calculateFahrenheit(celsius:celsius)
        text += String(celsius) + "," + String(fahrenheit) + "\n"
    }

    do {
        try text.write(toFile: filename, atomically: true, encoding: .utf8)
    } catch {
        print("Error creating ", filename)
        print(error.localizedDescription)
    }
}

func readFile(filename:String) {
    var text = ""

    do {
        text = try String(contentsOfFile: filename, encoding: .utf8)

        let lines = text.components(separatedBy:"\n")
        for line in lines {
            print(line)
        }
    } catch {
        print("Error reading " + filename)
        print(error.localizedDescription)
    }
}

func appendFile(filename:String) {
    var text: String
    var fahrenheit: Double

    do {
        text = try String(contentsOfFile: filename, encoding: .utf8)

        for celsius in stride(from: 51.0, through: 100.0, by: 1.0) {
            fahrenheit = calculateFahrenheit(celsius:celsius)
            text += String(celsius) + "," + String(fahrenheit) + "\n"
        }

        try text.write(toFile: filename, atomically: true, encoding: .utf8)
    } catch {
        print("Error appending to ", filename)
        print(error.localizedDescription)
    }
}

func deleteFile(filename:String) {
    do {
        let fileManager = FileManager.default
        try fileManager.removeItem(atPath:filename)
    } catch {
        print("Error deleting", filename)
        print(error.localizedDescription)
    }
}

func main() {
    let filename:String = "~file.txt"

    if (fileExists(filename:filename)) {
        print("File already exists.")
    }
    else {
        createFile(filename:filename)
        readFile(filename:filename)
        appendFile(filename:filename)
        readFile(filename:filename)
        deleteFile(filename:filename)
    }
}
        
main()

Try It[edit]

Copy and paste the code above into one of the following free online development environments or use your own Swift compiler / interpreter / IDE.

See Also[edit]