Dart Requires Chilkat v11.1.0+

Regular Expression with Named Capture Groups

See more Regular Expressions Examples

Demonstrates regular expressions with named capture groups.

See the sample code below.

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

In PCRE2, named capture groups allow you to assign a name to a capturing group, making it easier to reference by name instead of number.

Syntax

(?<name>pattern)

or

(?'name'pattern)

Example

(?<first>\w+)\s+(?<last>\w+)

Applied to:

"John Smith"

Produces:

• first: John
• last: Smith

Dart

import 'package:chilkat/chilkat.dart';

void main() {
  final subject = 'John Smith';
  final pattern = '(?<first>\\w+)\\s+(?<last>\\w+)';

  final sb = CkStringBuilder();
  sb.append(subject);

  final json = CkJsonObject();
  json.emitCompact = false;

  final timeoutMs = 2000;
  final numMatches = sb.regexMatch(pattern, json, timeoutMs);
  if (numMatches < 0) {
    // Probably an error in the regular expression.
    // Suggestion: Use AI to help create and/or diagnose regular expressions.
    print(sb.lastErrorText);
    return;
  }

  // Examine the matches:
  print(json.emit());

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

  // {
  //   "named": {
  //     "first": 1,
  //     "last": 2
  //   },
  //   "match": [
  //     {
  //       "group": [
  //         {
  //           "cap": "John Smith",
  //           "idx": 0,
  //           "len": 10
  //         },
  //         {
  //           "cap": "John",
  //           "idx": 0,
  //           "len": 4
  //         },
  //         {
  //           "cap": "Smith",
  //           "idx": 5,
  //           "len": 5
  //         }
  //       ]
  //     }
  //   ]
  // }

  // The capture group index is obtained by looking up the name in the JSON result.
  // For example:

  json.i = json.intOf('named.first');
  print('first: ${json.stringOf('match[0].group[i].cap')}');

  json.i = json.intOf('named.last');
  print('last: ${json.stringOf('match[0].group[i].cap')}');

  // Output is: 

  // first: John
  // last: Smith
}