how to use regular expressions in swift?

Question

I am trying to write a JSON parser in swift. I am writing functions for parsing different parts of JSON code. I wrote a string parser which detects a string from the JSON data, by checking the start with \" and if I meet with another \" it is separated and returned as a String but when I met with this JSON text:

{"gd$etag": "W\/\"D0QCQX4zfCp7I2A9XRZQFkw.\""}

the function I wrote failed in the above case since in the value part it has to recognise the whole as String while mine is working to collect only

W\/

Since I gave the condition as starting and ending with \" when I searched online I understood it is something in relation to regular expressions. So help me out to solve this!

Why reinvent the wheel? Use NSJSONSerialization (or 3rd party libs like SwiftyJSON). — Martin R
– Martin R, Commented Apr 25, 2015 at 14:42
@MartinR I really like the ObjectMapper library. But I think he's just wondering how to detect \"SAMPLE TEXT\" in a string. — Tobias
– Tobias, Commented Apr 25, 2015 at 15:29
I am just a noob to programming so I started doing as a project and get strong with fundas! And my main aim is to make it pure swift! — Karthik
– Karthik, Commented Apr 25, 2015 at 15:36
I am pretty sure that the question how to parse a string with nested escaped quotes with regular expressions has been answered before. – Apart from that, parsing JSON with regular expressions is probably a bad idea (think of strings in an array of dictionaries ...) — Martin R
– Martin R, Commented Apr 25, 2015 at 15:37
I just realised swift doesn't support regular expressions and I just found another way to sort this problem — Karthik
– Karthik, Commented Apr 29, 2015 at 15:37

Tobias · Accepted Answer · 2015-04-25 15:41:48Z

1

Is this what you were looking for?

import Foundation

let str: NSString = "W\\/\\\"D0QCQX4zfCp7I2A9XRZQFkw.\\\""
let regex = "\\\\\".*\\\\\""

// Finds range that starts with \" and ends with \"
let range = str.rangeOfString(regex, options: .RegularExpressionSearch)
let match: NSString = str.substringWithRange(range)

//Removes the \" from the start and end.
let innerString = match.substringWithRange(NSMakeRange(2, match.length-4))

answered Apr 25, 2015 at 15:41

Tobias

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2 Comments

Karthik Over a year ago

my agenda is to keep the code pure swift and I realised that swift doesn't support regex and I just worked with something else to solve this

Tobias Over a year ago

Yeah. I need to test out using regex with Emoji.

Karthik · Accepted Answer · 2015-04-29 15:39:21Z

if first(jsonString) == "\"" {
        jsonString.removeAtIndex(jsonString.startIndex)
        for elem in jsonString {
            if elem == "\\" {
                s = 1
                parsedString.append(elem)
                jsonString.removeAtIndex(jsonString.startIndex)
                continue
            }
            if s == 1 && elem == "\""{
                parsedString.append(elem)
                jsonString.removeAtIndex(jsonString.startIndex)
                s = 0
                continue
            }
            else if elem == "\""{
                jsonString.removeAtIndex(jsonString.startIndex)
                break
            }
            parsedString.append(elem)
            jsonString.removeAtIndex(jsonString.startIndex)
            s = 0
        }

This code lets me solve my issue to keep it pure swift.

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