Deco Deco - 3 years ago 131
Swift Question

Why does having more than one capture group in my regex crash my app?

Regardless of what the regex is, >1 capture group will crash this code with the following error.

Terminating app due to uncaught exception 'NSRangeException', reason: '-[__NSCFString substringWithRange:]: Range {9223372036854775807, 0} out of bounds; string length 279'

public extension String
{
//Multi use parsing function
func regexParse(pattern:String, captureGroup:Int, caseSensitive:Bool) ->[String]
{
do
{
//Creates empty results array.
var resultsArray = [""]

//Sets Case sensitivity
var caseSensitivity = NSRegularExpressionOptions.CaseInsensitive
if(caseSensitive)
{
caseSensitivity = NSRegularExpressionOptions.init(rawValue: 0)
}

//Sets regex to correct pattern
let regex = try NSRegularExpression(pattern: pattern, options: caseSensitivity)
//Converts string to NSString as swift doesn't support regex
let nsString = self as NSString

//Sets parsing range to the entire string
let all = NSMakeRange(0, nsString.length)

//Enumerates through all matches and extracts the 1st capture bracket for each match and adds it to the resultsArray.

regex.enumerateMatchesInString(self, options: NSMatchingOptions(rawValue: 0), range: all)
{
(result: NSTextCheckingResult?, _, _) in let theResult = nsString.substringWithRange(result!.rangeAtIndex(captureGroup))
resultsArray.append(theResult)
} //!!>>>>>>>>Error occurs here after skipping MatchingOptions content.!!
return resultsArray

}
catch
{
print("Invalid regex")
return(["Error"])
}
}


}

Answer Source

Range {9223372036854775807, 0} is {NSNotFound, 0}, that means there is no match.

From the documentation

Some regular expressions (though not the example pattern) can successfully match a zero-length range, so the comparison of the resulting range with {NSNotFound, 0} is the most reliable way to determine whether there was a match or not

Implement a check in enumerateMatchesInString for example

regex.enumerateMatchesInString(self, options: [], range: all) { (result: NSTextCheckingResult?, _, _) in
    let capturedRange = result!.rangeAtIndex(captureGroup)
    if !NSEqualRanges(capturedRange, NSMakeRange(NSNotFound, 0)) {
       let theResult = nsString.substringWithRange(capturedRange)
       resultsArray.append(theResult)
    }
}
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