C#

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

C#

bool success = false;

string subject = "John Smith";
string pattern = "(?<first>\\w+)\\s+(?<last>\\w+)";

Chilkat.StringBuilder sb = new Chilkat.StringBuilder();
sb.Append(subject);

Chilkat.JsonObject json = new Chilkat.JsonObject();
json.EmitCompact = false;

int timeoutMs = 2000;
int 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.
    Debug.WriteLine(sb.LastErrorText);
    return;
}

//  Examine the matches:
Debug.WriteLine(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");
Debug.WriteLine("first: " + json.StringOf("match[0].group[i].cap"));

json.I = json.IntOf("named.last");
Debug.WriteLine("last: " + json.StringOf("match[0].group[i].cap"));

//  Output is: 

//  first: John
//  last: Smith