Objective-C

Regular Expression with Capture Groups

See more Regular Expressions Examples

Note: Chilkat uses PCRE2. See PCRE2 Regular Expressions
Also see: PCRE2 Performance

Demonstrates the following PCRE2 regular expression:

See the sample code below.

Name:\s+(\w+)\s+(\w+),\s+Email:\s+(\S+)

And apply it to this string:

Name: John Smith, Email: john.smith@example.com

---

Regex Components Explained

Part	Meaning	Matched Text
"Name:"	Matches the literal text "Name:"	"Name:"
"\s+"	Matches one or more whitespace characters (spaces, tabs, etc.)	(space)
"(\w+)"	Capture Group 1: One or more word characters ("a-zA-Z0-9_")	"John"
"\s+"	More whitespace	(space)
"(\w+)"	Capture Group 2: Another word (the last name)	"Smith"
","	A literal comma	","
"\s+"	Whitespace again	(space)
"Email:"	Matches the literal "Email:"	"Email:"
"\s+"	Whitespace	(space)
"(\S+)"	Capture Group 3: One or more non-whitespace characters	"john.smith@example.com"

---

Matches for Your Example String

String:

"Name: John Smith, Email: john.smith@example.com"

Regex Match Groups:

Group	Captured Value
Group 1	"John"
Group 2	"Smith"
Group 3	"john.smith@example.com"

---

Notes on Character Classes

• \w matches [a-zA-Z0-9_] — so it doesn’t include punctuation like a period.
• \S matches any non-whitespace character, so it’s good for capturing an email.

Objective-C

#import <NSString.h>
#import <CkoStringBuilder.h>
#import <CkoJsonObject.h>

BOOL success = NO;

NSString *subject = @"Name: John Smith, Email: john.smith@example.com";
NSString *pattern = @"Name:\\s+(\\w+)\\s+(\\w+),\\s+Email:\\s+(\\S+)";

CkoStringBuilder *sb = [[CkoStringBuilder alloc] init];
[sb Append: subject];

CkoJsonObject *json = [[CkoJsonObject alloc] init];
json.EmitCompact = NO;

int timeoutMs = 2000;
int numMatches = [[sb RegexMatch: pattern json: json timeoutMs: [NSNumber numberWithInt: timeoutMs]] intValue];
if (numMatches < 0) {
    // Probably an error in the regular expression.
    // Suggestion: Use AI to help create and/or diagnose regular expressions.
    NSLog(@"%@",sb.LastErrorText);
    return;
}

// Examine the matches:
NSLog(@"%@",[json Emit]);

// This is the JSON with the match information.
// See the JSON parsing code below to get the matched capture group values.

// Important:  Capture group 0 always contains the entire match — that is, the portion of the input string that matches the full regular expression.

// {
//   "match": [
//     {
//       "group": [
//         {
//           "cap": "Name: John Smith, Email: john.smith@example.com",
//           "idx": 0,
//           "len": 47
//         },
//         {
//           "cap": "John",
//           "idx": 6,
//           "len": 4
//         },
//         {
//           "cap": "Smith",
//           "idx": 11,
//           "len": 5
//         },
//         {
//           "cap": "john.smith@example.com",
//           "idx": 25,
//           "len": 22
//         }
//       ]
//     }
//   ]
// }

NSString *cap = 0;
int i = 0;
int matchCount = [[json SizeOfArray: @"match"] intValue];
while (i < matchCount) {
    NSLog(@"%@%d%@",@"Match ",i + 1,@":");
    json.I = [NSNumber numberWithInt: i];
    int j = 0;
    int numCaptureGroups = [[json SizeOfArray: @"match[i].group"] intValue];
    while (j < numCaptureGroups) {
        json.J = [NSNumber numberWithInt: j];
        cap = [json StringOf: @"match[i].group[j].cap"];
        NSLog(@"%d%@%@",j,@": ",cap);
        j = j + 1;
    }

    i = i + 1;
}

// Capture group 0 always contains the entire match — that is, the portion of the input string that matches the full regular expression.

// Output

// Match 1:
// 0: Name: John Smith, Email: john.smith@example.com
// 1: John
// 2: Smith
// 3: john.smith@example.com