NSCheckingResult Range property not set to {NSNotfound, 0}?

Question

From looking at the documents for NSTextCheckingResult , I got the impression that if no match was found in the NSRegularExpression search, the range property for NSCheckingResult would be set to {NSNotFound,0}

From my test below, I find that if no match is found, then the NSCheckingResult range NSCheckingResult set to {0,0} . This is a small point, but I just wanted to clarify my understanding of how this works.

 // REGEXPRESSION NSString *textBuffer = @"1234567890"; NSString *pattern = @"(([AZ]+))"; NSRegularExpression *regExp = [NSRegularExpression regularExpressionWithPattern:pattern options:0 error:nil]; NSTextCheckingResult *match = [regExp firstMatchInString:textBuffer options:0 range:NSMakeRange(0, [textBuffer length])]; // ERROR CHECK if([match range].location == NSNotFound) NSLog(@"Match Not found"); NSLog(@"location: %d", [match range].location); NSLog(@"length : %d", [match range].length); // OUTPUT location: 0 length : 0 

EDIT: In this example, NSTextCheckingResult *match set to nil , which is probably due to the location and length returning zero (message to the nil object).

 if(!match) NSLog(@"Match Not Found"); 

Therefore, I assume that NSNotFound returns only when there are several capture groups, where it represents an empty group.

Answer 1

Yes, this is due to a null match. {NSNotFound, 0} may be returned rangeAtIndex: for a group that did not participate in the match.