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

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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.

C++

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

void ChilkatSample(void)
    {
    bool success = false;

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

    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";

    // 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
    //         }
    //       ]
    //     }
    //   ]
    // }

    const char *cap = 0;
    int i = 0;
    int matchCount = json.SizeOfArray("match");
    while (i < matchCount) {
        std::cout << "Match " << (i + 1) << ":" << "\r\n";
        json.put_I(i);
        int j = 0;
        int numCaptureGroups = json.SizeOfArray("match[i].group");
        while (j < numCaptureGroups) {
            json.put_J(j);
            cap = json.stringOf("match[i].group[j].cap");
            std::cout << j << ": " << cap << "\r\n";
            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
    }