Getting wrong range with regex in Objective-C - ios

Question

I have the following string: "Title: " and I am using regex in Objective-C to extract the "/books/1/title" part from the string. (The string can contain multiple expressions) The regex is as follows <\?(.+?)\?>. My problem is that it matches the whole string(from index 0 to 24) and not the content between the tags.
The code is as follows:
NSString *object = #"Title: <?/books/1/title?>";
NSMutableString *newString = [[NSMutableString alloc] initWithString:object];
NSString *pattern = #"<\?(.+?)\?>";
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:pattern
options:0 error:NULL];
NSArray *matches = [regex matchesInString:object options:0 range:NSMakeRange(0, [object length])];
for (NSInteger i = [matches count]-1; i>=0 ; i--) {
NSTextCheckingResult * match = [matches objectAtIndex:i];
if (match != nil && [match rangeAtIndex:0].location != NSNotFound && [match numberOfRanges] == 2) {
NSRange part1Range = [match rangeAtIndex:1];
NSLog(#"%lu %lu", (unsigned long)part1Range.location, (unsigned long)part1Range.length);
}
}

Answer 1

It looks like you have incorrectly escaped the question marks: you used a single backslash, but Objective-C compiler needs two slashes in a string literal in order to represent a single backslash:
NSString *pattern = #"<\\?(.+?)\\?>";
Without the extra slash single slashes are not becoming part of the string, so regex engine sees this expression <?(.+?)?>, treats the opening angular bracket as optional, and then proceeds to matching the whole text up to the closing angular bracket.
One way to escape meta-characters, such as question marks and dots, is enclosing them into a character class instead of using a backslash. This expression is equivalent to yours, but it does not additional escaping of slashes:
NSString *pattern = #"<[?](.+?)[?]>";