Regex in Objective-C

Regex stands for Regular Expression. It is a sequence of characters that form a search pattern. Regex is used to search, replace, and validate text based on a certain pattern.

In Objective-C, regex is implemented through the NSRegularExpression class which provides methods for regex search and replacement.

Here are some examples of using regex in Objective-C:

1. Search for a pattern in a string and return all matches:

``objective-c NSString *str = @"The quick brown fox jumps over the lazy dog"; NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"[aeiouy]" options:NSRegularExpressionCaseInsensitive error:nil]; NSArray *matches = [regex matchesInString:str options:0 range:NSMakeRange(0, str.length)];


for (NSTextCheckingResult *match in matches) {

    NSLog(@"%@", [str substringWithRange:match.range]);

}
// Output: e u i o o u o e a



In this example, the regex pattern [aeiouy] searches for all vowels in the given string. The options parameter specifies that the search should not be case-sensitive. The method matchesInString returns an array of NSTextCheckingResult objects which contain the range of each match. The substringWithRange method is then used to extract the matched substring from the original string.
2. Replace all occurrences of a pattern with a replacement string:
objective-c

NSString *str = @"Hello, world!";

NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"world" options:NSRegularExpressionCaseInsensitive error:nil];

NSString *result = [regex stringByReplacingMatchesInString:str options:0 range:NSMakeRange(0, str.length) withTemplate:@"universe"];
NSLog(@"%@", result);
// Output: Hello, universe!



In this example, the regex pattern world is used to search for the word "world" in the given string. The stringByReplacingMatchesInString method then replaces all occurrences of the pattern with the replacement string "universe".
3. Validate a string against a pattern:
objective-c

NSString *str = @"example@gmail.com";

NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"\\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}\\b" options:NSRegularExpressionCaseInsensitive error:nil];

BOOL isValidEmail = [regex firstMatchInString:str options:0 range:NSMakeRange(0, str.length)] != nil;
NSLog(@"%@", isValidEmail ? @"Valid email" : @"Invalid email");

// Output: Valid email`

In this example, the regex pattern \b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}\b is used to validate an email address. The firstMatchInString method returns the first match of the pattern in the given string, or nil if there is no match. The Boolean variable isValidEmail` is then set based on whether a match was found.

Regex in Objective-C

See this concept in other languages