Zig Requires Chilkat v11.1.0+

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

Zig

const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    const subject = "John Anders, +_+_+ Mary Robins $$$$";
    const pattern = "(?<first>\\w+)\\s+(?<last>\\w+)";

    const sb = try chilkat.StringBuilder.init();
    defer sb.deinit();
    sb.append(subject) catch {};

    const json = try chilkat.JsonObject.init();
    defer json.deinit();
    json.setEmitCompact(false);

    const timeout_ms = 2000;
    var num_matches: i32 = sb.regexMatch(pattern, json, timeout_ms);
    if (num_matches < 0) {
        // Probably an error in the regular expression.
        // Suggestion: Use AI to help create and/or diagnose regular expressions.
        std.debug.print("{s}\n", .{try sb.getLastErrorText(alloc)});
        return;
    }

    // Examine the matches:
    std.debug.print("{s}\n", .{try json.emit(alloc)});

    // 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 $$$$

    const first_name_idx = json.intOf("named.first");
    const last_name_idx = json.intOf("named.last");

    const sb_temp = try chilkat.StringBuilder.init();
    defer sb_temp.deinit();

    var i: i32 = 0;
    num_matches = json.sizeOfArray("match");
    while (i < num_matches) {
        json.setI(i);

        // The replacement string for the first name will be all uppercase.
        json.setJ(first_name_idx);
        sb_temp.clear();
        json.stringOfSb("match[i].group[j].cap", sb_temp) catch {};
        sb_temp.toUppercase() catch {};
        json.updateSb("match[i].group[j].rep", sb_temp) catch {};

        // Append "on" to the last name.
        json.setJ(last_name_idx);
        sb_temp.clear();
        json.stringOfSb("match[i].group[j].cap", sb_temp) catch {};
        sb_temp.append("on") catch {};
        json.updateSb("match[i].group[j].rep", sb_temp) catch {};

        i = i + 1;
    }

    // The JSON now has replacement strings:
    std.debug.print("{s}\n", .{try json.emit(alloc)});

    // {
    //   "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.
    sb.regexReplace(json) catch {
        std.debug.print("{s}\n", .{try sb.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("Result after doing replacements:\n", .{});
    std.debug.print("{s}\n", .{try sb.getAsString(alloc)});

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