How can i use multidimensional arrays to store multiple elements, then retrieve elements

Question

So I'm trying to create a small car park management system. What I want to do is to have users input their vehicle number and it will store it into an array. I also want other elements like check in time, a serial number, vehicle type, etc. to be stored with the vehicle number.

I want to know how I can use a multidimensional array to store all what I mentioned into the vehicle number so that when the user types their veh number again, it would show all other elements stored within that.

Sorry if I'm not making it clear enough.

Why not make a `class Vehicle` and then have a `std::vector`? Then you class can have data members like time, serial number, etc. — Cory Kramer, Feb 28 '22 at 12:40
@CoryKramer I thought the same. Or if you don't want to create a class you can just use `std::map> vehicle_data;`. — The Coding Fox, Feb 28 '22 at 12:42

score 5 · Answer 1 · answered Feb 28 '22 at 12:43

The first step is to use a struct to organize your data, e.g.:

struct Vehicle {
    int id;
    int serial;
    VehicleType type;
};

The second question is what is the approprate container for your objects. An array is fine in general as you can easily append to it. That would then be

std::vector<Vehicle> vehicles;

However whenever you want to lookup a vehicle by its id, you will need to go through all of them to find the matching one. More efficient would be a map. There are several variants but for starters, a regular one will be fine:

std::map<int, Vehicle> vehicles;

Example insertion:

// given int vin, int serial
vehicles[vin] = {vin, serial, VehicleType::Car}

An alternative would be the std::unordered_map.

You need to familiarize yourself with these containers so you can learn about their proper use and advantages/disadvantages. A good starter is here: How to choose between map and unordered_map?

score 3 · Answer 2 · 2022-02-28T16:01:50.617

3

Sounds like you're looking for something like a map: https://www.cplusplus.com/reference/map/map/ where the key is your vehicle number and the mapped value is the vehicle's details (whatever you'd like to add there).

Edit: As an example in your case

std::map<int, vehicle> vehicleMap;

To use that vehicleMap properly you should

define a struct or class of type vehicle
create the objects of type vehicle you want to use
add your desired details to the vehicle objects
insert the vehicle objects to the map with vehicleMap.insert(int, vehicle).

then you can use vehicleMap.find(<int>); to retrieve all the details of your vehicle. : )

edited Feb 28 '22 at 16:01

answered Feb 28 '22 at 12:42

2

You can actually give a quick little example to use maps in this case if possible. – The Coding Fox Feb 28 '22 at 12:48
Thanks for the suggestion, edited to add an example. – Feb 28 '22 at 13:00
1

Hey @johnnydead83, your example is great unitl the insert statement. You probably mean `vehicleMap.insert({id, vehicle})` or similar - as otherwise the key is missing. – ypnos Feb 28 '22 at 15:14
Thanks, @ypnos I did indeed miss that. Fixed! – Feb 28 '22 at 16:01

The Coding Fox · Answer 3 · 2022-02-28T14:11:26.747

1

You can always use maps for this purpose as such:

std::map<int, Vehicle> vehicle_data;

..and here's a simple example:

#include <iostream>
#include <string>
#include <map>

class Vehicle
{
public:
    std::string name;

    Vehicle(std::string _name) : name(_name) { }
};

int main()
{
    std::map<int, Vehicle> vehicle_data;

    vehicle_data.insert({ 1, Vehicle("vehicle name 1")});
    vehicle_data.insert({ 3, Vehicle("vehicle name 3") });
    vehicle_data.insert({ 2, Vehicle("vehicle name 2") });

    auto it1 = vehicle_data.find({ 1 });
    auto it2 = vehicle_data.find({ 2 });
    auto it3 = vehicle_data.find({ 4 });

    if (it1 != vehicle_data.end()) std::cout << it1->second.name << std::endl;
    if (it2 != vehicle_data.end()) std::cout << it2->second.name << std::endl;
    if (it3 != vehicle_data.end()) std::cout << it3->second.name << std::endl;
}

In the above code, I've inserted 3 vehicles into vehicle_data and then I've used find() to get the iterator pointing to the element with int value of 1, 2, and 4 and then printed the second element's (Vehicle's) name.

edited Feb 28 '22 at 14:11

answered Feb 28 '22 at 12:52

The Coding Fox

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better do not use `find` wihtout checking if it retunred `end()`. – 463035818_is_not_an_ai Feb 28 '22 at 13:01
@463035818_is_not_a_number Yep that makes sense. I've edited the answer. – The Coding Fox Feb 28 '22 at 13:04
it will not "cause errors". Dereferencing the end iterator is plain undefined behavior. In the second code you need not look up the elements twice, you can use the iterators you already found – 463035818_is_not_an_ai Feb 28 '22 at 13:12
That's what I meant by errors. But I've edited the answer. – The Coding Fox Feb 28 '22 at 13:19
ub is not "errors", in some sense its the opposite, because typically compilers to not diagnose it – 463035818_is_not_an_ai Feb 28 '22 at 13:22
@463035818_is_not_a_number Alright. I actually was saying that in the sense of compiler errors and exceptions. But thanks for informing me. – The Coding Fox Feb 28 '22 at 13:37
better remove the code with UB altogether. Ppl tend to copy past code without understanding what it does, and your first code can do anything – 463035818_is_not_an_ai Feb 28 '22 at 14:03

How can i use multidimensional arrays to store multiple elements, then retrieve elements

3 Answers3