Is there a way to display cpp map in a specific way

Question

I need to display the following seats to users and be able to reserve them and cancel the reservation.

class luxaryBus {
    public:
            std::map<std::string, int> seats{ {"1A", 0}, {"1B", 0}, {"1C", 0}, {"1D", 0},{"1E", 0},
                                        {"2A", 0}, {"2B", 0}, {"2C", 0}, {"2D", 0},{"2E", 0},
                                        {"3A", 0}, {"3B", 0}, {"3C", 0}, {"3D", 0},{"3E", 0},
                                        {"4A", 0}, {"44", 0}, {"4C", 0}, {"4D", 0},{"4E", 0},
                                        {"5A", 0}, {"5B", 0}, {"5C", 0}, {"5D", 0},{"5E", 0},
                                        {"6A", 0}, {"6B", 0}, {"6C", 0}, {"6D", 0},{"6E", 0},
                                        {"7A", 0}, {"7B", 0}, {"7C", 0}, {"7D", 0},{"7E", 0},
                                        {"8A", 0}, {"8B", 0}, {"8C", 0}, {"8D", 0},{"8E", 0},
                                        {"9A", 0}, {"9B", 0}, {"9C", 0}, {"9D", 0},{"9E", 0},
                                        {"10 A", 0}, {"10B", 0}, {"10C", 0}, {"10D", 0},{"10E", 0},
                                        {"11 A", 0}, {"11B", 0}};
    
    void displaySeats();
}



void luxaryBus::displaySeats()
{
int test = 0;
    for (const auto& p : this->seats) {
        if (test == 5) {
            std::cout << std::endl;
            test = 0;
        }
        test++;
        std::cout << p.first << p.second << "\t ";
    }
}

Apparently, it is sorting the strings in a way that doesn't work for me:

1A 10A 10B 10C etc...

I tried unordered_map also but no matter what I do I cannot make map display the seats in the way I want (1A, 1B, 1C, 1D, 1E).

1A 1B 1C 1D 1E

2A 2B 2C 2D 2E....

Tried to change the seat name to A1 B1 C1 D1... Obviously I am new to C++. I know that map is ordered.And I know that using unordered_map there is no way I can guarantee the way the map will be displayed.

My question is, can I use map in a specific way so I can display it in a way that I want to. Or, is there another data structure in c++ that I can use for my task.

Array was my first choice, however, I found it difficult to follow which seat was sold and handle cancellation. Now I can make it work with 2 arrays, one for string representation and one for handling the operations with reservation and cancellation.

Can anyone give me a suggestion how to tackle this problem?

Answer 1

std::map uses comparison operator< to compare keys in the map. However, the problem is that strings are being compared lexicographically, so both "1A" and "10A" are smaller than "1B" .

But you can use a more complicated map: std::map<std::pair<int, char>, int> in which key is number and character. Here number will be compared as numbers and characters as characters.

Use it like:

std::map<std::pair<int, char>, int> map{{{1, 'B'}, 0}, {{1, 'C'}, 0}};

PS: you can override output like here:

std::ostream& operator<<(std::ostream& out, const std::map<std::pair<int, char>, int>& map)
{
    for (const auto& p : map) {
        out << p.first.first << p.first.second << " ";
    }
    return out;
}

int main() {
    std::map<std::pair<int, char>, int> map{{{1, 'B'}, 0}, {{1, 'C'}, 0}};

    std::cout << map;
    return 0;
}

Answer 2

You can put in a custom comparator to sort the data in the map in the order you want.

For this, you can refer to the following code:

    auto seatCompare = [](std::string const& seat1, std::string const& seat2) -> bool {
        std::smatch result1;
        std::smatch result2;
        std::regex pattern(R"(([0-9]+)([a-z A-Z]+))");
        if (!regex_match(seat1, result1, pattern) || !regex_match(seat2, result2, pattern)) {
            throw std::runtime_error("Seat name invalid!");
        }
        if (std::stoi(result1[1]) == std::stoi(result2[1])) {
            return result1[2] < result2[2];
        }
        return std::stoi(result1[1]) < std::stoi(result2[1]);
    };
    std::map<std::string, int, decltype(seatCompare)> seats(seatCompare);
    seats = { {"1A", 0}, {"1B", 0}, {"1C", 0}, {"1D", 0},{"1E", 0},
              {"2A", 0}, {"2B", 0}, {"2C", 0}, {"2D", 0},{"2E", 0},
              {"3A", 0}, {"3B", 0}, {"3C", 0}, {"3D", 0},{"3E", 0},
              {"4A", 0}, {"4B", 0}, {"4C", 0}, {"4D", 0},{"4E", 0},
              {"5A", 0}, {"5B", 0}, {"5C", 0}, {"5D", 0},{"5E", 0},
              {"6A", 0}, {"6B", 0}, {"6C", 0}, {"6D", 0},{"6E", 0},
              {"7A", 0}, {"7B", 0}, {"7C", 0}, {"7D", 0},{"7E", 0},
              {"8A", 0}, {"8B", 0}, {"8C", 0}, {"8D", 0},{"8E", 0},
              {"9A", 0}, {"9B", 0}, {"9C", 0}, {"9D", 0},{"9E", 0},
              {"10A", 0}, {"10B", 0}, {"10C", 0}, {"10D", 0},{"10E", 0},
              {"11A", 0}, {"11B", 0}};

or C++98 style

struct SeatCompare {
    bool operator()(std::string const& seat1, std::string const& seat2)
    {
        std::smatch result1;
        std::smatch result2;
        std::regex pattern(R"(([0-9]+)([a-z A-Z]+))");
        if (!regex_match(seat1, result1, pattern) || !regex_match(seat2, result2, pattern)) {
            throw std::runtime_error("Seat name invalid!");
        }
        if (std::stoi(result1[1]) == std::stoi(result2[1])) {
            return result1[2] < result2[2];
        }
        return std::stoi(result1[1]) < std::stoi(result2[1]);
    }
};

std::map<std::string, int, SeatCompare> seats{ 
    {"1A", 0}, {"1B", 0}, {"1C", 0}, {"1D", 0},{"1E", 0},
    {"2A", 0}, {"2B", 0}, {"2C", 0}, {"2D", 0},{"2E", 0},
    {"3A", 0}, {"3B", 0}, {"3C", 0}, {"3D", 0},{"3E", 0},
    {"4A", 0}, {"4B", 0}, {"4C", 0}, {"4D", 0},{"4E", 0},
    {"5A", 0}, {"5B", 0}, {"5C", 0}, {"5D", 0},{"5E", 0},
    {"6A", 0}, {"6B", 0}, {"6C", 0}, {"6D", 0},{"6E", 0},
    {"7A", 0}, {"7B", 0}, {"7C", 0}, {"7D", 0},{"7E", 0},
    {"8A", 0}, {"8B", 0}, {"8C", 0}, {"8D", 0},{"8E", 0},
    {"9A", 0}, {"9B", 0}, {"9C", 0}, {"9D", 0},{"9E", 0},
    {"10A", 0}, {"10B", 0}, {"10C", 0}, {"10D", 0},{"10E", 0},
    {"11A", 0}, {"11B", 0}};