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++

#include <CkStringBuilder.h>
#include <CkJsonObject.h>

void ChilkatSample(void)
    {
    bool success = false;

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

    CkStringBuilder sb;
    sb.Append(subject);

    CkJsonObject json;
    json.put_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.
        std::cout << sb.lastErrorText() << "\r\n";
        return;
    }

    //  Examine the matches:
    std::cout << json.emit() << "\r\n";

    //  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.put_I(json.IntOf("named.first"));
    std::cout << "first: " << json.stringOf("match[0].group[i].cap") << "\r\n";

    json.put_I(json.IntOf("named.last"));
    std::cout << "last: " << json.stringOf("match[0].group[i].cap") << "\r\n";

    //  Output is: 

    //  first: John
    //  last: Smith
    }