Read a text file line by line in Swift?
Solution 1
Swift 3.0
if let path = Bundle.main.path(forResource: "TextFile", ofType: "txt") {
do {
let data = try String(contentsOfFile: path, encoding: .utf8)
let myStrings = data.components(separatedBy: .newlines)
TextView.text = myStrings.joined(separator: ", ")
} catch {
print(error)
}
}
The variable myStrings
should be each line of the data.
The code used is from: Reading file line by line in iOS SDK written in Obj-C and using NSString
Check edit history for previous versions of Swift.
Solution 2
Swift 5.5
The solution below shows how to read one line at a time. This is quite different from reading the entire contents into memory. Reading line-by-line scales well if you have a large file to read. Putting an entire file into memory does not scale well for large files.
The example below uses a while loop that quits when there are no more lines, but you can choose a different number of lines to read if you wish.
The code works as follows:
- create a URL that tells where the file is located
- make sure the file exists
- open the file for reading
- set up some initial variables for reading
- read each line using
getLine()
- close the file and free the buffer when done
You could make the code less verbose if you wish; I have included comments to explain what the variables' purposes are.
Swift 5.5
import Cocoa
// get URL to the the documents directory in the sandbox
let home = FileManager.default.homeDirectoryForCurrentUser
// add a filename
let fileUrl = home
.appendingPathComponent("Documents")
.appendingPathComponent("my_file")
.appendingPathExtension("txt")
// make sure the file exists
guard FileManager.default.fileExists(atPath: fileUrl.path) else {
preconditionFailure("file expected at \(fileUrl.absoluteString) is missing")
}
// open the file for reading
// note: user should be prompted the first time to allow reading from this location
guard let filePointer:UnsafeMutablePointer<FILE> = fopen(fileUrl.path,"r") else {
preconditionFailure("Could not open file at \(fileUrl.absoluteString)")
}
// a pointer to a null-terminated, UTF-8 encoded sequence of bytes
var lineByteArrayPointer: UnsafeMutablePointer<CChar>? = nil
// see the official Swift documentation for more information on the `defer` statement
// https://docs.swift.org/swift-book/ReferenceManual/Statements.html#grammar_defer-statement
defer {
// remember to close the file when done
fclose(filePointer)
// The buffer should be freed by even if getline() failed.
lineByteArrayPointer?.deallocate()
}
// the smallest multiple of 16 that will fit the byte array for this line
var lineCap: Int = 0
// initial iteration
var bytesRead = getline(&lineByteArrayPointer, &lineCap, filePointer)
while (bytesRead > 0) {
// note: this translates the sequence of bytes to a string using UTF-8 interpretation
let lineAsString = String.init(cString:lineByteArrayPointer!)
// do whatever you need to do with this single line of text
// for debugging, can print it
print(lineAsString)
// updates number of bytes read, for the next iteration
bytesRead = getline(&lineByteArrayPointer, &lineCap, filePointer)
}
Solution 3
This is not pretty, but I believe it works (on Swift 5). This uses the underlying POSIX getline
command for iteration and file reading.
typealias LineState = (
// pointer to a C string representing a line
linePtr:UnsafeMutablePointer<CChar>?,
linecap:Int,
filePtr:UnsafeMutablePointer<FILE>?
)
/// Returns a sequence which iterates through all lines of the the file at the URL.
///
/// - Parameter url: file URL of a file to read
/// - Returns: a Sequence which lazily iterates through lines of the file
///
/// - warning: the caller of this function **must** iterate through all lines of the file, since aborting iteration midway will leak memory and a file pointer
/// - precondition: the file must be UTF8-encoded (which includes, ASCII-encoded)
func lines(ofFile url:URL) -> UnfoldSequence<String,LineState>
{
let initialState:LineState = (linePtr:nil, linecap:0, filePtr:fopen(fileURL.path,"r"))
return sequence(state: initialState, next: { (state) -> String? in
if getline(&state.linePtr, &state.linecap, state.filePtr) > 0,
let theLine = state.linePtr {
return String.init(cString:theLine)
}
else {
if let actualLine = state.linePtr { free(actualLine) }
fclose(state.filePtr)
return nil
}
})
}
Here is how you might use it:
for line in lines(ofFile:myFileURL) {
print(line)
}
Solution 4
Update for Swift 2.0 / Xcode 7.2
do {
if let path = NSBundle.mainBundle().pathForResource("TextFile", ofType: "txt"){
let data = try String(contentsOfFile:path, encoding: NSUTF8StringEncoding)
let myStrings = data.componentsSeparatedByCharactersInSet(NSCharacterSet.newlineCharacterSet())
print(myStrings)
}
} catch let err as NSError {
//do sth with Error
print(err)
}
Also worth to mention is that this code reads a file which is in the project folder (since pathForResource is used), and not in e.g. the documents folder of the device
Solution 5
Probably the simplest, and easiest way to do this in Swift 5.0, would be the following:
import Foundation
// Determine the file name
let filename = "main.swift"
// Read the contents of the specified file
let contents = try! String(contentsOfFile: filename)
// Split the file into separate lines
let lines = contents.split(separator:"\n")
// Iterate over each line and print the line
for line in lines {
print("\(line)")
}
Note: This reads the entire file into memory, and then just iterates over the file in memory to produce lines....
Credit goes to: https://wiki.codermerlin.com/mediawiki/index.php/Code_Snippet:_Print_a_File_Line-by-Line
ScarletEnvy
Updated on January 10, 2022Comments
-
ScarletEnvy over 2 years
I just started learning Swift. I have got my code to read from the text file, and the App displays the content of the entire text file. How can I display line by line and call upon that line multiple times?
TextFile.txt
contains the following:1. Banana 2. Apple 3. pear 4. strawberry 5. blueberry 6. blackcurrant
The following is what currently have..
if let path = NSBundle.mainBundle().pathForResource("TextFile", ofType: "txt"){ var data = String(contentsOfFile:path, encoding: NSUTF8StringEncoding, error: nil) if let content = (data){ TextView.text = content }
If there is another way of doing this please let me know. It would be much appreciated.