brasskazoo - Real-life adventures in Software and Build Engineering

As of iOS 4.0 and OSX 10.7, Apple provides a class NSRegularExpression which implements the use of regular expressions in Objective C.

An immutable instance of NSRegularExpression is created with a regex pattern and options, and upon execution, can create NSTextCheckingResult for each match. NSTextCheckingResult uses NSRange objects to describe the location of match groups within the source string - so that by applying the range to the source string, you can extract the resulting matched text.

Code

The following code demonstrates a regex in action. The search expression matches words starting with a vowel, and ending in 'd' or 's'. It will print the total number of matches, and then each group of each match. Output is below.

NSString *strSource = @"The NSRegularExpression class is used to represent and apply regular expressions to Unicode strings. An instance of this class is an immutable representation of a compiled regular expression pattern and various option flags. The pattern syntax currently supported is that specified by ICU.";

NSError *errRegex = NULL; 
NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"\\b(a|e|i|o|u)\\w+(s|d)\\b" options:NSRegularExpressionCaseInsensitive error:&errRegex];

NSUInteger countMatches = [regex numberOfMatchesInString:strSource options:0 range:NSMakeRange(0, [strSource length])];
NSLog(@"Number of Matches: %ld", countMatches); 

NSLog(@"-----"); 

[regex enumerateMatchesInString:strSource
                        options:0
                          range:NSMakeRange(0, [strSource length])
                     usingBlock:^(NSTextCheckingResult *match, NSMatchingFlags flags, BOOL *stop) {

    NSLog(@"Ranges: %ld", [match numberOfRanges]);

    NSString *matchFull = [strSource substringWithRange:[match range]]; 
    NSLog(@"Match: %@", matchFull); 

    for (int i = 0; i < [match numberOfRanges]; i++) {
        NSLog(@"\tRange %i: %@", i, 
            [strSource substringWithRange:[match rangeAtIndex:i]]);
    } 
}]; 

if (errRegex) { 
    NSLog(@"%@", errRegex); 
}

Output

RegexTest[23743:403] Number of Matches: 4
RegexTest[23743:403] ----- 
RegexTest[23743:403] Ranges: 3 
RegexTest[23743:403] Match: used 
RegexTest[23743:403]  Range 0: used 
RegexTest[23743:403]  Range 1: u 
RegexTest[23743:403]  Range 2: d 
RegexTest[23743:403] Ranges: 3 
RegexTest[23743:403] Match: and 
RegexTest[23743:403]  Range 0: and 
RegexTest[23743:403]  Range 1: a 
RegexTest[23743:403]  Range 2: d 
RegexTest[23743:403] Ranges: 3 
RegexTest[23743:403] Match: expressions 
RegexTest[23743:403]  Range 0: expressions 
RegexTest[23743:403]  Range 1: e 
RegexTest[23743:403]  Range 2: s 
RegexTest[23743:403] Ranges: 3 
RegexTest[23743:403] Match: and 
RegexTest[23743:403]  Range 0: and 
RegexTest[23743:403]  Range 1: a 
RegexTest[23743:403]  Range 2: d

Using Regular Expressions in Objective C

Code

Output

Read More...