Using Regular Expressions in Objective C

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

Read More…

  1. Apple Developer Documentation