Randomize string with any length

std::string random_string(size_t length) {
    auto randchar = []() -> char {
        const char charset[] =
            "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
            "abcdefghijklmnopqrstuvwxyz";
        const size_t max_index = (sizeof(charset) - 1);
        return charset[rand() % max_index];
    };
    std::string str(length, 0);
    std::generate_n(str.begin(), length, randchar);

    return str;
}