I know that to program in STDIN and STDOUT, we need to make an command line project in Xcode.
But how do I take a standard input in playground.
Whenever I try to run such code in playground
var input = readLine()!
I always get this error
Execution was interrupted, reason: EXC_BAD_INSTRUCTION
(Code=EXC_l386_INVOP, subcode=0x0)
Is it possible to take STDIN in playground or not?
UPDATE
I know this error is because of nil input variable but want to know how to overcome this nil value.
Fixed Solution for SWIFT 3
To make it work, Create a new command line tool project.
Go to "File" -> "New" -> "Project" -> "macOS" -> "Command Line Tool".
import Foundation
print("Hello, World!")
func solveMefirst(firstNo: Int , secondNo: Int) -> Int {
return firstNo + secondNo
}
func input() -> String {
let keyboard = FileHandle.standardInput
let inputData = keyboard.availableData
return NSString(data: inputData, encoding:String.Encoding.utf8.rawValue) as! String
}
let num1 = readLine()
let num2 = readLine()
var IntNum1 = Int(num1!)
var IntNum2 = Int(num2!)
print("Addition of numbers is : \(solveMefirst(firstNo: IntNum1!, secondNo: IntNum2!))")
And run the project using CMD + R
Playground can not read an input from the commend line.
You can use a custom "readLine()" function and a global input variable, each element in the input array is presenting a line:
import Foundation
var currentLine = 0
let input = ["5", "5 6 3"]
func readLine() -> String? {
if currentLine < input.endIndex {
let line = input[currentLine]
currentLine += 1
return line
} else {
return nil
}
}
let firstLine = readLine() // 5
let secondLine = readLine() // 5 6 3
let thirdLine = readLine() // nil
Try using Optional Chaining:
if let input = readLine() {
print("Input: \(input)")
} else {
print("No input.")
}
Go to
New > Project > MacOs > Command Line Tool
then you can apply :
let value1: String?
value1 = readLine()
print(value1 ?? "")
"" for the default value
For getting input from command line, like Console.ReadLine... Chalkers has a solution as follows.
func input() -> String {
var keyboard = NSFileHandle.fileHandleWithStandardInput()
var inputData = keyboard.availableData
return NSString(data: inputData, encoding:NSUTF8StringEncoding) as! String
}
please ask for further if it doesn't work Vinod.
Related
I have a complicated AppleScript that returns a list of strings that I need to access from Swift. I've boiled it down to a simple example and I just can't figure out how to map the AppleScript strings to an array of Swift strings.
let listOfStringsScript = """
set listOfStrings to { "one", "two", "three" }
"""
if let scriptObject = NSAppleScript(source: listOfStringsScript) {
var errorDict: NSDictionary? = nil
let resultDescriptor = scriptObject.executeAndReturnError(&errorDict)
if errorDict == nil {
// TODO: convert the resultDescriptor (NSAppleEventDescriptor) into an array of strings
print(resultDescriptor)
// OUTPUT: <NSAppleEventDescriptor: [ 'utxt'("one"), 'utxt'("two"), 'utxt'("three") ]>
}
}
Answer with help from #Alexander and #MartinR:
extension NSAppleEventDescriptor {
func toStringArray() -> [String] {
guard let listDescriptor = self.coerce(toDescriptorType: typeAEList) else {
return []
}
return (0..<listDescriptor.numberOfItems)
.compactMap { listDescriptor.atIndex($0 + 1)?.stringValue }
}
}
...
let resultDescriptor = scriptObject.executeAndReturnError(&errorDict)
let subjectLines = resultDescriptor.toStringArray()
An alternative is to gather the Apple Script result as lines of text separated by line breaks and then parse the string in Swift.
So break up the Apple Script result using
set AppleScript's text item delimiters to linefeed
Then simply parse
let selectedItems = scriptExecuted.stringValue!
let selectedItemsFiltered = selectedItems.components(separatedBy: .newlines)
.components returns a string array
I have received this response from the server and I am sure there must be a more efficient way to convert it into an object.
I have the following response:
[
id=2997,rapidViewId=62,state=ACTIVE,name=Sprint7,startDate=2018-11-20T10:28:37.256Z,endDate=2018-11-30T10:28:00.000Z,completeDate=<null>,sequence=2992,goal=none
]
How do I convert it nicely into a well formed swift object in the simplest way?
Here is my attempt which gives me just the Sprint Value
if sprintJiraCustomField.count > 0 {
let stringOutput = sprintJiraCustomField.first?.stringValue // convert output to String
let name = stringOutput?.components(separatedBy: "name=") // get name section from string
let nameFieldRaw = name![1].components(separatedBy: ",") // split out to the comma
let nameValue = nameFieldRaw.first!
sprintDetail = nameValue// show name field
}
Not sure what format you want but the below code will produce an array of tuples (key, value) but all values are strings so I guess another conversion is needed afterwards
let items = stringOutput.components(separatedBy: ",").compactMap( {pair -> (String, String) in
let keyValue = pair.components(separatedBy: "=")
return (keyValue[0], keyValue[1])
})
This is a work for reduce:
let keyValueStrings = yourString.components(separatedBy: ",")
let dictionary = keyValueStrings.reduce([String: String]()) {
(var aggregate: [String: String], element: String) -> [String: String] in
let elements = element.componentsSeparatedByString("=")
let key = elements[0]
// replace nil with the value you want to use if there is no value
let value = (elements.count > 1) ? elements[1] : nil
aggregate[key] = value
return aggregate
}
This is a functional approach, but you can achieve the same using a for iteration.
So then you can use Swift’s basic way of mapping. for example you will have your custom object struct. First, you will add an init method to it. Then map your object like this:
init(with dictionary: [String: Any]?) {
guard let dictionary = dictionary else { return }
attribute = dictionary["attrName"] as? String
}
let customObjec = CustomStruct(dictionary: dictionary)
We already have some suggestion to first split the string at each comma and then split each part at the equals sign. This is rather easy to code and works well, but it is not very efficient as every character has to be checked multiple times. Writing a proper parser using Scanner is just as easy, but will run faster.
Basically the scanner can check if a given string is at the current position or give you the substring up to the next occurrence of a separator.
With that the algorithm would have the following steps:
Create scanner with the input string
Check for the opening bracket, otherwise fail
Scan up to the first =. This is the key
Consume the =
Scan up to the first , or ]. This is the value
Store the key/value pair
If there is a , consume it and continue with step 3
Consume the final ].
Sadly the Scanner API is not very Swift-friendly. With a small extension it is much easier to use:
extension Scanner {
func scanString(_ string: String) -> Bool {
return scanString(string, into: nil)
}
func scanUpTo(_ delimiter: String) -> String? {
var result: NSString? = nil
guard scanUpTo(delimiter, into: &result) else { return nil }
return result as String?
}
func scanUpTo(_ characters: CharacterSet) -> String? {
var result: NSString? = nil
guard scanUpToCharacters(from: characters, into: &result) else { return nil }
return result as String?
}
}
With this we can write the parse function like this:
func parse(_ list: String) -> [String: String]? {
let scanner = Scanner(string: list)
guard scanner.scanString("[") else { return nil }
var result: [String: String] = [:]
let endOfPair: CharacterSet = [",", "]"]
repeat {
guard
let key = scanner.scanUpTo("="),
scanner.scanString("="),
let value = scanner.scanUpTo(endOfPair)
else {
return nil
}
result[key] = value
} while scanner.scanString(",")
guard scanner.scanString("]") else { return nil }
return result
}
Testing in Playground I read a whole file in an array of String, one string per line.
But what I need is a specific line only:
let dir = try? FileManager.default.url(for: .documentDirectory,
in: .userDomainMask, appropriateFor: nil, create: true)
let fileURL = dir!.appendingPathComponent("test").appendingPathExtension("txt")
let text: [String] = try String(contentsOf: fileURL).components(separatedBy: NSCharacterSet.newlines)
let i = 2 // computed before, here to simplify
print(text[i])
There is a way to avoid reading the complete big file?
I'm guessing you mean that you want to retrieve the index without manually searching the array with, say, a for-in loop.
In Swift 4 you can use Array.index(where:) in combination with the StringProtocol's generic contains(_:) function to find what you're looking for.
Let's imagine you're looking for the first line containing the text "important stuff" in your text: [String] array.
You could use:
text.index(where: { $0.contains("important stuff") })
Behind the scenes, Swift is looping to find the text, but with built-in enhancements, this should perform better than manually looping through the text array.
Note that the result of this search could be nil if no matching lines are present. Therefore, you'll need to ensure it's not nil before using the result:
Force unwrap the result (risking the dreaded fatal error: unexpectedly found nil while unwrapping an Optional value):
print(text[lineIndex!)
Or, use an if let statement:
if let lineIndex = stringArray.index(where: { $0.contains("important stuff") }) {
print(text[lineIndex])
}
else {
print("Sorry; didn't find any 'important stuff' in the array.")
}
Or, use a guard statement:
guard let lineIndex = text.index(where: {$0.contains("important stuff")}) else {
print("Sorry; didn't find any 'important stuff' in the array.")
return
}
print(text[lineIndex])
To find a specific line without reading the entire file in, you could use this StreamReader answer. It contains code that worked in Swift 3. I tested it in Swift 4, as well: see my GitHub repo, TEST-StreamReader, for my test code.
You would still have to loop to get to the right line, but then break the loop once you've retrieved that line.
Here's the StreamReader class from that SO answer:
class StreamReader {
let encoding : String.Encoding
let chunkSize : Int
var fileHandle : FileHandle!
let delimData : Data
var buffer : Data
var atEof : Bool
init?(path: String, delimiter: String = "\n", encoding: String.Encoding = .utf8,
chunkSize: Int = 4096) {
guard let fileHandle = FileHandle(forReadingAtPath: path),
let delimData = delimiter.data(using: encoding) else {
return nil
}
self.encoding = encoding
self.chunkSize = chunkSize
self.fileHandle = fileHandle
self.delimData = delimData
self.buffer = Data(capacity: chunkSize)
self.atEof = false
}
deinit {
self.close()
}
/// Return next line, or nil on EOF.
func nextLine() -> String? {
precondition(fileHandle != nil, "Attempt to read from closed file")
// Read data chunks from file until a line delimiter is found:
while !atEof {
if let range = buffer.range(of: delimData) {
// Convert complete line (excluding the delimiter) to a string:
let line = String(data: buffer.subdata(in: 0..<range.lowerBound), encoding: encoding)
// Remove line (and the delimiter) from the buffer:
buffer.removeSubrange(0..<range.upperBound)
return line
}
let tmpData = fileHandle.readData(ofLength: chunkSize)
if tmpData.count > 0 {
buffer.append(tmpData)
} else {
// EOF or read error.
atEof = true
if buffer.count > 0 {
// Buffer contains last line in file (not terminated by delimiter).
let line = String(data: buffer as Data, encoding: encoding)
buffer.count = 0
return line
}
}
}
return nil
}
/// Start reading from the beginning of file.
func rewind() -> Void {
fileHandle.seek(toFileOffset: 0)
buffer.count = 0
atEof = false
}
/// Close the underlying file. No reading must be done after calling this method.
func close() -> Void {
fileHandle?.closeFile()
fileHandle = nil
}
}
extension StreamReader : Sequence {
func makeIterator() -> AnyIterator<String> {
return AnyIterator {
return self.nextLine()
}
}
}
i'm trying to create a simple user input but the only function that i have found in swift is this one
func input() -> String {
var keyboard = NSFileHandle.fileHandleWithStandardInput()
var inputData = keyboard.availableData
return NSString(data: inputData, encoding:NSUTF8StringEncoding) as String!
}
then i'm trying to convert input() to an Int for a mathematic operation (i'm using 1 as the input) with this
var inputToInt = input().toInt()!
in this point i get only nil i don't know what to do.
Swift 2.0 has a function called readLine() - using it is a much better idea than rolling your own.
http://swiftdoc.org/swift-2/func/readLine/
Your conversion to Int fails because the string contains newline. You can use this to clean it up:
let s = NSString(data: inputData, encoding:NSUTF8StringEncoding) as String!
if s.hasSuffix("\n") {
return s.substringToIndex(x.endIndex.predecessor())
} else {
return s
}
I have a String description that holds my sentence and want to capitalize only the first letter. I tried different things but most of them give me exceptions and errors. I'm using Xcode 6.
Here is what I tried so far:
let cap = [description.substringToIndex(advance(0,1))] as String
description = cap.uppercaseString + description.substringFromIndex(1)
It gives me:
Type 'String.Index' does not conform to protocol 'IntegerLiteralConvertible'
I tried:
func capitalizedStringWithLocale(locale:0) -> String
But I haven't figured out how to make it work.
In Swift 2, you can do
String(text.characters.first!).capitalizedString + String(text.characters.dropFirst())
Another possibility in Swift 3:
extension String {
func capitalizeFirst() -> String {
let firstIndex = self.index(startIndex, offsetBy: 1)
return self.substring(to: firstIndex).capitalized + self.substring(from: firstIndex).lowercased()
}
}
For Swift 4:
Warnings from above Swift 3 code:
'substring(to:)' is deprecated: Please use String slicing subscript
with a 'partial range upto' operator.
'substring(from:)' is deprecated: Please use String slicing subscript with a 'partial range from' operator.
Swift 4 solution:
extension String {
var capitalizedFirst: String {
guard !isEmpty else {
return self
}
let capitalizedFirstLetter = charAt(i: 0).uppercased()
let secondIndex = index(after: startIndex)
let remainingString = self[secondIndex..<endIndex]
let capitalizedString = "\(capitalizedFirstLetter)\(remainingString)"
return capitalizedString
}
}
Swift 5.0
Answer 1:
extension String {
func capitalizingFirstLetter() -> String {
return prefix(1).capitalized + dropFirst()
}
mutating func capitalizeFirstLetter() {
self = self.capitalizingFirstLetter()
}
}
Answer 2:
extension String {
func capitalizeFirstLetter() -> String {
return self.prefix(1).capitalized + dropFirst()
}
}
Answer 3:
extension String {
var capitalizeFirstLetter:String {
return self.prefix(1).capitalized + dropFirst()
}
}
import Foundation
// A lowercase string
let description = "the quick brown fox jumps over the lazy dog."
// The start index is the first letter
let first = description.startIndex
// The rest of the string goes from the position after the first letter
// to the end.
let rest = advance(first,1)..<description.endIndex
// Glue these two ranges together, with the first uppercased, and you'll
// get the result you want. Note that I'm using description[first...first]
// to get the first letter because I want a String, not a Character, which
// is what you'd get with description[first].
let capitalised = description[first...first].uppercaseString + description[rest]
// Result: "The quick brown fox jumps over the lazy dog."
You may want to make sure there's at least one character in your sentence before you start, as otherwise you'll get a runtime error trying to advance the index beyond the end of the string.
Here is how to do it in Swift 4; just in case if it helps anybody:
extension String {
func captalizeFirstCharacter() -> String {
var result = self
let substr1 = String(self[startIndex]).uppercased()
result.replaceSubrange(...startIndex, with: substr1)
return result
}
}
It won't mutate the original String.
extension String {
var capitalizedFirstLetter:String {
let string = self
return string.replacingCharacters(in: startIndex...startIndex, with: String(self[startIndex]).capitalized)
}
}
Answer:
let newSentence = sentence.capitalizedFirstLetter
For one or each word in string, you can use String's .capitalized property.
print("foo".capitalized) //prints: Foo
print("foo foo foo".capitalized) //prints: Foo Foo Foo
Swift 4.2 version:
extension String {
var firstCharCapitalized: String {
switch count {
case 0:
return self
case 1:
return uppercased()
default:
return self[startIndex].uppercased() + self[index(after: startIndex)...]
}
}
}
Simplest soulution for Swift 4.0.
Add as a computed property extension:
extension String {
var firstCapitalized: String {
var components = self.components(separatedBy: " ")
guard let first = components.first else {
return self
}
components[0] = first.capitalized
return components.joined(separator: " ")
}
}
Usage:
"hello world".firstCapitalized