std::string result;
    auto iter = std::sregex_iterator(input.begin(), input.end(), pattern);
    auto end = std::sregex_iterator();
    size_t lastPos = 0;

    for (; iter != end; ++iter) {
        const std::smatch& match = *iter;
        result.append(input, lastPos, match.position() - lastPos);

        // Convert hexadecimal codepoint to integer
        int codepoint = std::stoi(match[1].str(), nullptr, 16);

        // Append the Unicode character to the result string
        result.push_back(static_cast<char>(codepoint));

        // Update last position
        lastPos = match.position() + match.length();
    }

    // Append the rest of the input string
    result.append(input, lastPos, input.length() - lastPos);

    return result;