I want to get a string from a file. I've researched how to do it, and I've found the next code:
import Foundation
// Read data from this file.
let path = "/Users/samallen/file.txt"
do {
// Use contentsOfFile overload.
// ... Specify ASCII encoding.
// ... Ignore errors.
var data = try NSString(contentsOfFile: path,
encoding: String.Encoding.ascii.rawValue)
// If a value was returned, print it.
print(data)
}
The important part are the lines:
var data = try NSString(contentsOfFile: path,
encoding: String.Encoding.ascii.rawValue)
I looked in Apple's documentation about this and found init(contentsOfFile:usedEncoding:)
What I don't get is why you can use String(contentsOfFile:usedEncoding:) instead of init(contentsOfFile:usedEncoding:). Why can you replace String for init? I have seen somthing similar with UIImage.
Thanks in advance
Related
I have been playing with a json file in a playground and I've seen examples of reading the file like this:
do {
let jsonData = try String(contentsOf: url).data(using: .utf8)
} catch {
...
}
And like this:
do {
let jsonData = try Data(contentsOf: url)
} catch {
...
}
Is there a difference in the data? The only difference I see is the String data method is being formatted as UTF8 when read, where I am assuming the Data method is reading with a default format (UTF8 also??)? I can't see a difference in the data, however, but just want to make sure.
The difference is that String(contentsOf: url) tries to read text from that URL, whereas Data(contentsOf: url) reads the raw bytes.
Therefore, if the file at the URL is not a plain text file, String(contentsOf: url) could throw an error, whereas Data(contentsOf: url) would read it successfully.
Regarding the encoding, String(contentsOf: url) is undocumented, but from its implementation, we can see that it calls NSString.init(contentsOf:usedEncoding:):
public init(
contentsOf url: __shared URL
) throws {
let ns = try NSString(contentsOf: url, usedEncoding: nil)
self = String._unconditionallyBridgeFromObjectiveC(ns)
}
NSString.init(contentsOf:usedEncoding:) is documented:
Returns an NSString object initialized by reading data from a given URL and returns by reference the encoding used to interpret the data.
So apparently the encoding is guessed (?) and returned by reference, which is then ignored by String.init(contentsOf:), as it passed nil for the usedEncoding parameter.
This means that for some non-UTF-8 files, there is a chance of String(contentsOf:) guessing the correct encoding, and then data(using: .utf8) encodes the string to UTF-8 bytes, making the rest of your code work. If you had used Data(contentsOf:), you would be reading in the wrong encoding, and though it wouldn't throw an error, the JSON-parsing code later down the line probably would.
That said, JSON is supposed to be exchanged in UTF-8 (See RFC), so an error when you read a non-UTF-8 file is probably desired.
So basically, if we are choosing between these two options, just use Data(contentsOf:). It's simpler and less typing. You don't need to worry about thing like wrong encodings, or that the file is not plain text. If anything like that happens, it is not JSON, and the JSONDecoder later down the line would throw.
I need help figuring out how to write repeatedly to the same, open, output file.
I am using Swift 4.2. My searches and tests have turned up only code that writes a single text string to a file and then closes the file. The next opening overwrites the last one. An example is shown below.
The problem is that I need to be able to write large numbers of records (say, 1.5 million) and perform calculations on each record just before it is written to a file. That’s not feasible when the code will only write once before closing. I'm calling this "writing line by line", much like the opposite, to "read line by line."
I tried to find an option in various Swift write statements and SO posts, but everything seems to be geared toward writing once then closing the file. I tried an open for append, but that did not work and anyway it seems inefficient to open, close, reopen-append each time I want to write to a file. I tried some C code in Swift, using open(… and freopen(… but could not get something that the compiler wouldn't complain about. Hopefully, there is a way to do this all in Swift. The following code works nicely for one write.
let file0 = “test_file.txt”
let s0 = ("This is a test line of text")
do {
try s0.write(to: NSURL(fileURLWithPath: file0) as URL, atomically: false, encoding: String.Encoding.utf8)
} catch {
print("Problem writing to file0")
}
How can I adapt this code snippet to write a string, and then another and another etc, and before closing the file when it’s all done? If not with this, is there Swift code that will do the job?
Following are the essential code components needed to write to a file, line-by-line in Swift. First is some file management code to create a file if it does not exist, then there is code to print a series of example statements, followed by code to print to the file in a loop, and finally close the file. This code worked correctly in Swift 4.2. The difference between this and the method in the question is that the write statements in this code use a method of fileHandle! and the question shows a method of a Swift string.
print("Swift_Write_to_File_Test_1")
var outFilename: NSString = "test_file.txt"
// Begin file manager segment
// Check for file presence and create it if it does not exist
let filemgr = FileManager.default
let path = filemgr.urls(for: FileManager.SearchPathDirectory.documentDirectory, in: FileManager.SearchPathDomainMask.userDomainMask).last?.appendingPathComponent(outFilename as String)
if !filemgr.fileExists(atPath: (path?.absoluteString)!) {
filemgr.createFile(atPath: String(outFilename), contents:Data(" ".utf8), attributes: nil)
}
// End file manager Segment
// Open outFilename for writing – this does not create a file
let fileHandle = FileHandle(forWritingAtPath: outFilename as String)
if(fileHandle == nil)
{
print("Open of outFilename forWritingAtPath: failed. \nCheck whether the file already exists. \nIt should already exist.\n");
exit(0)
}
var str: NSString = "2. Test string from NSString.\n";
var str0: String = "3. Test string from a Swift String.\n"
var str1: NSString = "4. Test string from NSString.\n";
fileHandle!.write("1. Text String in-line with code statement.\n".data(using: .utf8)!)
fileHandle!.write(String(str).data(using: .utf8)!)
fileHandle!.write(str0.data(using: .utf8)!)
fileHandle!.write(String(str1).data(using: .utf8)!)
fileHandle!.write("5. Text String in-line with code statement.\n".data(using: .utf8)!)
fileHandle!.write("6. Text in a loop follows: \n".data(using: .utf8)!)
for i in 0...5
{
//Assemble a string then write it to the file.
var s0: String = ""
s0 = String(i)
//s0.append(" ... some text here.\n") // See improvement below
s0 += " ... some text here.\n" // This is a better than .append
fileHandle!.write(s0.data(using: .utf8)!)
}
// End of file-writing segment
fileHandle!.closeFile()
This worked for me in Swift 5:
func writeFile() -> Bool
{
let outFilename: String = "test_file.txt"
let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first
let outFilePath = documentsURL!.appendingPathComponent(outFilename).path
let fileManager = FileManager.default
// If file exists, remove it
if fileManager.fileExists(atPath: outFilePath)
{
do { try fileManager.removeItem(atPath: outFilePath) }
catch { return false }
}
// Create file and open it for writing
fileManager.createFile(atPath: outFilePath, contents:Data(" ".utf8), attributes: nil)
let fileHandle = FileHandle(forWritingAtPath: outFilePath)
if fileHandle == nil
{
return false
}
else
{
// Write data
fileHandle!.write("Test line 1\n".data(using: .utf8)!)
fileHandle!.write("Test line 2\n".data(using: .utf8)!)
fileHandle!.write("Test line 3\n".data(using: .utf8)!)
// Close file
fileHandle!.closeFile()
return true
}
}
I need to send an array through HTTP to my swift client but I'm not sure how to convert the bytes I've received to a swift array.
I've looked it up on google multiple times with multiple different ways of saying what I'm trying to do but all I'm getting is topics that say "convert byte array to swift string"
AF.request(exampleUrl).response { response in
if let data = response.data, let s = String(data: data, encoding: .utf8) {
debugPrint(s)
let myArray = decodeSomehow(data: data)
debugPrint(myArray[0]) // hooray
}
}
I need to be able to decode arrays sent from my server but my efforts to find the solution to this problem have yielded no results.
btw server is made with firebase functions and is run on Google frontend
and coded with typescript
also to clarify I do not want to take the bytes and put them into an array, I want to decode the bytes into what they originally were on the server aka an array (originally a typescript array but if it is possible to make it a swift array that would be 👌)
The Data class is an advance version of [UInt8]. Normally, working directly with Data class is recommended. If you really want to convert it to [UInt8], simply
let arr = [UInt8](data)
or
let arr = Array(data)
Hope it helps... (Thanks LEO for your best Comment)
let string = "Hello World"
print(Array(string.utf8))
I figured out how to do what I was trying to do...
In the end, I solved my own problem lol
all I needed to do was decode it with swiftyjson
thank you all for your answers
AF.request(exampleUrl).response { response in
if let data = response.data, let s = String(data: data, encoding: .utf8) {
let arr = JSON(data)
debugPrint(arr)
debugPrint(arr[0][0])
debugPrint(s)
}
}
output
I have a .docx file in my temporary storage:
let location: NSURL = NSURL.fileURLWithPath(NSTemporaryDirectory())
let file_Name = location.URLByAppendingPathComponent("5 November 2016.docx")
What I now want to do is extract the text inside this document. But I cannot seem to find any converters or methods of doing this.
I have tried this:
let file_Content = try? NSString(contentsOfFile: String(file_Name), encoding: NSUTF8StringEncoding)
print(file_Content)
However it prints nil.
So how do I read the text in a docx file?
Swift 4, Xcode 9.1, OSX targets from 10.10 to 10.13
I have found that the following code extracts text handily from a Word .doc file, which then easily goes into a string. (The attributed string contains formatting information that might be parsed to good effect.) The main info that I wanted to convey was the bit about using .docFormat to specify the document type.
let openPanel = NSOpenPanel()
var fileString = String("")
var fileData = NSData()
let fileURL = openPanel.url
do {
fileData = try NSData(contentsOf: fileURL!)
if let tryForString = try? NSAttributedString(data: fileData as Data, options: [
.documentType: NSAttributedString.DocumentType.docFormat,
.characterEncoding: String.Encoding.utf8.rawValue
], documentAttributes: nil) {
fileString = tryForString.string
} else {
fileString = "Data conversion error."
}
fileString = fileString.trimmingCharacters(in: .whitespacesAndNewlines)
} catch {
print("Word Document File Not Found")
}
Your initial issue is with how you get the string from the URL. String(File_Name) is not the correct way to convert a file URL into a file path. The proper way is to use the path function.
let location = NSURL.fileURLWithPath(NSTemporaryDirectory())
let fileURL = location.URLByAppendingPathComponent("My File.docx")
let fileContent = try? NSString(contentsOfFile: fileURL.path, encoding: NSUTF8StringEncoding)
Note the many changes. Use proper naming conventions. Name variables more clearly.
Now here's the thing. This still won't work because a docx file is a zipped up collection of XML and other files. You can't load a docx file into an NSString. You would need to use NSData to load the zip contents. Then you would need to unzip it. Then you would need to go through all of the files and find the desired text. It's far from trivial and it is far beyond the scope of a single stack overflow post.
I'm trying to learn the new Swift programming language. It looks great, but I'm having a difficult time doing something as simple as reading the content of a local .txt file.
I have tried the few examples I could find through Google, but they give compile errors, like this answer here: Read and write data from text file
If I tweak the code a bit, it works, but can only read from a special location within the project.
Why isn't it just as simple to read a .txt file with Swift as it is with for instance Ruby? And how would I go about reading the content of a file located at ~/file.txt?
Thnx
If you have a tilde in your path you can try this:
let location = "~/file.txt".stringByExpandingTildeInPath
let fileContent = NSString(contentsOfFile: location, encoding: NSUTF8StringEncoding, error: nil)
otherwise just use this:
let location = "/Users/you/Desktop/test.txt"
let fileContent = NSString(contentsOfFile: location, encoding: NSUTF8StringEncoding, error: nil)
This gives you a string representation of the file, which I assumed is what you want.
You can use NSData(contentsOfFile: location) to get a binary representation, but you would normally do that for, say, music files and not a text file.
Update: With Xcode 7 and Swift 2 this doesn't work anymore. You can now use
let location = NSString(string:"~/file.txt").stringByExpandingTildeInPath
let fileContent = try? NSString(contentsOfFile: location, encoding: NSUTF8StringEncoding)
let file = "/Users/user/Documents/text.txt"
let path=URL(fileURLWithPath: file)
let text=try? String(contentsOf: path)
This would work:
let path = "~/file.txt"
let expandedPath = path.stringByExpandingTildeInPath
let data: NSData? = NSData(contentsOfFile: expandedPath)
if let fileData = data {
let content = NSString(data: fileData, encoding:NSUTF8StringEncoding) as String
}
Note that data may be nil, so you should check for that.
EDIT:
Don't forget conditional unwrapping - looks much nicer ;)
Relative path tip:
Instead of doing this:
NSString("~/file.txt").stringByExpandingTildeInPath
You can do this:
"\(NSHomeDirectory())/file.txt"
You may find this tool useful to not only read from file in Swift but also parse it simultaneously: https://github.com/shoumikhin/StreamScanner
Just specify the file path and data delimiters like this (see readme for more options):
import StreamScanner
if let input = NSFileHandle(forReadingAtPath: "/file/path")
{
let scanner = StreamScanner(source: input, delimiters: NSCharacterSet(charactersInString: ":\n")) //separate data by colons and newlines
while let field: String = scanner.read()
{
//use field
}
}
Hope, this helps.
Using the answer by Atomix, this will work in Swift 4:
let location = NSString(string: "~/test.txt").expandingTildeInPath
let fileContent = try? NSString(contentsOfFile: location, encoding: String.Encoding.utf8.rawValue)
This worked for me in Swift 2.1, XCode7 to get the location and print the contents of CSV. ( you can create a simple CSV in Text Wrangler)
override func viewDidLoad() {
super.viewDidLoad()
let location = NSString(string:"/Users/*Myusername*/Documents/myCSVfile.csv")
let fileContent = try? NSString(contentsOfFile: location as String, encoding: NSUTF8StringEncoding)
print(fileContent)
}
Swift 4:
let filePath = "/Users/UserName/Desktop/FolderName/FileName.txt"
let fullPath = NSString(string: filePath).expandingTildeInPath
do
{
let fileContent = try NSString(contentsOfFile: fullPath, encoding: String.Encoding.utf8.rawValue)
print(fileContent)
}
catch
{
print(error)
}
filename doesn't need to have scheme like file://, and can be relative like ../docs/test.txt.
Remember to catch any error thrown, or rethrow.
let url = URL(fileURLWithPath: filename)
let contents = try String(contentsOf: url, encoding: .utf8)