How to check if string matches a regular expression in objective-c?

Another way to do this, which is a bit simpler than using NSPredicate, is an almost undocumented option to NSString's -rangeOfString:options: method:

NSRange range = [string rangeOfString:@"^\\w+$" options:NSRegularExpressionSearch];
BOOL matches = range.location != NSNotFound;

I say "almost undocumented", because the method itself doesn't list the option as available, but if you happen upon the documentation for the Search and Comparison operators and find NSRegularExpressionSearch you'll see that it's a valid option for the -rangeOfString... methods since OS X 10.7 and iOS 3.2.

I've used NSPredicate for that purpose:

NSString *someRegexp = ...; 
NSPredicate *myTest = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", someRegexp]; 

if ([myTest evaluateWithObject: testString]){
//Matches
}

NSRegularExpression is another option:

http://developer.apple.com/library/ios/#documentation/Foundation/Reference/NSRegularExpression_Class/Reference/Reference.html

Use the -isMatchedByRegex: method.

if([someString isMatchedByRegex:@"^[0-9a-fA-F]+:"] == YES) { NSLog(@"Matched!\n"); }