C++

Regular Expression Replace Capture Groups

See more Regular Expressions Examples

Demonstrates replacing capture groups for a regular expression.

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

C++

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

void ChilkatSample(void)
    {
    bool success = false;

    const char *subject = "John Anders, +_+_+ Mary Robins $$$$";
    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";

    // There are 2 matches:

    // {
    //   "named": {
    //     "first": 1,
    //     "last": 2
    //   },
    //   "match": [
    //     {
    //       "group": [
    //         {
    //           "cap": "John Anders",
    //           "idx": 0,
    //           "len": 11
    //         },
    //         {
    //           "cap": "John",
    //           "idx": 0,
    //           "len": 4
    //         },
    //         {
    //           "cap": "Anders",
    //           "idx": 5,
    //           "len": 6
    //         }
    //       ]
    //     },
    //     {
    //       "group": [
    //         {
    //           "cap": "Mary Robins",
    //           "idx": 19,
    //           "len": 11
    //         },
    //         {
    //           "cap": "Mary",
    //           "idx": 19,
    //           "len": 4
    //         },
    //         {
    //           "cap": "Robins",
    //           "idx": 24,
    //           "len": 6
    //         }
    //       ]
    //     }
    //   ]
    // }

    // To replace capture groups, write code to examine each capture group within
    // each match, and provide a replacement string.
    // Then call RegexReplace.

    // For example, let's capitalize the first names, and add append "on" to the last name.
    // After doing replacements, we should get:  JOHN Anderson, +_+_+ MARY Robinson $$$$

    int firstNameIdx = json.IntOf("named.first");
    int lastNameIdx = json.IntOf("named.last");

    CkStringBuilder sbTemp;

    int i = 0;
    numMatches = json.SizeOfArray("match");
    while (i < numMatches) {

        json.put_I(i);

        // The replacement string for the first name will be all uppercase.
        json.put_J(firstNameIdx);
        sbTemp.Clear();
        json.StringOfSb("match[i].group[j].cap",sbTemp);
        sbTemp.ToUppercase();
        json.UpdateSb("match[i].group[j].rep",sbTemp);

        // Append "on" to the last name.
        json.put_J(lastNameIdx);
        sbTemp.Clear();
        json.StringOfSb("match[i].group[j].cap",sbTemp);
        sbTemp.Append("on");
        json.UpdateSb("match[i].group[j].rep",sbTemp);

        i = i + 1;
    }

    // The JSON now has replacement strings:
    std::cout << json.emit() << "\r\n";

    // {
    //   "named": {
    //     "first": 1,
    //     "last": 2
    //   },
    //   "match": [
    //     {
    //       "group": [
    //         {
    //           "cap": "John Anders",
    //           "idx": 0,
    //           "len": 11
    //         },
    //         {
    //           "cap": "John",
    //           "idx": 0,
    //           "len": 4,
    //           "rep": "JOHN"
    //         },
    //         {
    //           "cap": "Anders",
    //           "idx": 5,
    //           "len": 6,
    //           "rep": "Anderson"
    //         }
    //       ]
    //     },
    //     {
    //       "group": [
    //         {
    //           "cap": "Mary Robins",
    //           "idx": 19,
    //           "len": 11
    //         },
    //         {
    //           "cap": "Mary",
    //           "idx": 19,
    //           "len": 4,
    //           "rep": "MARY"
    //         },
    //         {
    //           "cap": "Robins",
    //           "idx": 24,
    //           "len": 6,
    //           "rep": "Robinson"
    //         }
    //       ]
    //     }
    //   ]
    // }

    // Call RegexReplace to update the StringBuilder with the replacements.
    success = sb.RegexReplace(json);
    if (success == false) {
        std::cout << sb.lastErrorText() << "\r\n";
        return;
    }

    std::cout << "Result after doing replacements:" << "\r\n";
    std::cout << sb.getAsString() << "\r\n";

    // Result after doing replacements:
    // JOHN Anderson, +_+_+ MARY Robinson $$$$
    }