Regular expression, specifying optional capture groups? - objective-c

Question

Is there a way to write a regular expression pattern that will create one or two groups based on the input text. (i.e.)
// ONE
NSString *pattern = #""; ([0-9]+).([0-9]+)
NSString *inputText = #"ThisIs MyTest72.56String";
// OUTPUT match = 72.56, group1 = 72, group2 = 56
What I am trying to get is:
// TWO
NSString *pattern = #""; ([0-9]+).([0-9]+)
NSString *inputText = #"ThisIs MyTest72String";
// OUTPUT match = 72, group1 = 72, group2 = Empty
I was thinking I could use (?:) but that just removes the group
What I am after is:
Text = "ThisIs MyTest72String"
Match = 72
Group1 = 72
Group2 = Empty
Text = "ThisIs MyTest72.56String"
Match = 72.56
Group1 = 72
Group2 = 56
EDIT:
This sort of works, although I would like to get rid of the "S" in the initial match.
Pattern = ([0-9]+).([0-9]*)
Text = "ThisIs MyTest72String"
Match = 72S
Group1 = 72 //RangeAtIndex:1 {13,2}
Group2 = Empty //RangeAtIndex:2 {16,0}
Text = "ThisIs MyTest72.56String"
Match = 72.56
Group1 = 72
Group2 = 56
This is close, but in the case of "Empty" (Group2) I was expecting the rangeAtIndex:2 to equal NSNotFound. The docs say "The range {NSNotFound, 0} is returned if one of the capture groups did not participate in this particular match" does the group being empty not count as "Not participating"?

Answer 1

Does this give you what you want?
([0-9]+)(?:\.([0-9]+))?
I've escaped the decimal place (which you hadn't, unsure if this is needed in your target language) and grouped the decimal and everything after it as a optional non captured group.
Should just be a matter of checking for the existence of a second group.

Answer 2

How about this:
NSString *inputText = #"ThisIs MyTest72.56String";
// Setup an NSError object to catch any failures
NSError *error = NULL;
// create the NSRegularExpression object and initialize it with a pattern
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:#"\\d+.\\d+" options:NSRegularExpressionCaseInsensitive error:&error];
// create an NSRange object using our regex object for the first match in the string httpline
NSRange rangeOfFirstMatch = [regex rangeOfFirstMatchInString:inputText options:0 range:NSMakeRange(0, [inputText length])];
// check that our NSRange object is not equal to range of NSNotFound
if (!NSEqualRanges(rangeOfFirstMatch, NSMakeRange(NSNotFound, 0))) {
// Since we know that we found a match, get the substring from the parent string by using our NSRange object
NSString *substringForFirstMatch = [inputText substringWithRange:rangeOfFirstMatch];
NSLog(#"Extracted string: %#",substringForFirstMatch); // Extracted string: 72.56
regex = [NSRegularExpression regularExpressionWithPattern:#"\\d+" options:NSRegularExpressionCaseInsensitive error:&error];
NSArray *matches = [regex matchesInString:substringForFirstMatch options:0 range:NSMakeRange(0, [substringForFirstMatch length])];
for (NSTextCheckingResult *match in matches) {
NSString *matchString = [substringForFirstMatch substringWithRange:[match range]];
NSLog(#"match string: %#", matchString);
// match string: 72
// match string: 56
}
}

Answer 3

Use this pattern:
pattern = #"([0-9]+)\.([0-9]+)?";
and then in the NSTextCheckingResult check if the group range location is NSNotFound.
Example code:
NSString *pattern = #"([0-9]+).([0-9]+)?";
NSString *string = #"ThisIs MyTest72.56String";
//NSString *string = #"ThisIs MyTest72.XXString";
NSRegularExpression *regex = [NSRegularExpression
regularExpressionWithPattern:pattern
options:NSRegularExpressionCaseInsensitive
error:nil];
NSTextCheckingResult *match = [regex firstMatchInString:string options:0 range:NSMakeRange(0, string.length)];
for (int groupNumber=1; groupNumber<match.numberOfRanges; groupNumber+=1) {
NSRange groupRange = [match rangeAtIndex:groupNumber];
if (groupRange.location != NSNotFound)
NSLog(#"match %d: '%#'", groupNumber, [string substringWithRange:groupRange]);
else
NSLog(#"match %d: '%#'", groupNumber, #"");
}
NSLog output:
match 1: '72'
match 2: '56'
With the second pattern "match 2: ''".