Multidimensional array to store three different data types?

Question

I have a set of three values pairs that I want to store in an array, each value with different type.

[string][int][double] for storing things like [John][12][40.025] [Amy][20][16000.411] and I want to be able to retrieve the values by location. What container should I use?

I have looked through many answers but most of them were about two data types, and I don't know which one better suit my case.

You can use std::tuple<string,int,double>, and get<N> to access the Nth tuple element. You can store these tuples in an array or vector. — cigien
– cigien, Commented Jun 17, 2020 at 14:18
You could also use std::vector<mystruct> where mystuct is a class or struct that contains your 3 different types. — drescherjm
– drescherjm, Commented Jun 17, 2020 at 14:23

eerorika · Accepted Answer · 2020-06-17 14:38:20Z

3

This is what classes are for:

struct data {
    std::string name;
    int         name_describing_this_variable;
    double      another_descriptive_name;
};

You can store instances of this class in an array:

data arr[] {
    {"John", 12, 40.025},
    {"Amy",  20, 16000.411},
};

edited Jun 17, 2020 at 14:38

answered Jun 17, 2020 at 14:24

eerorika

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5 Comments

reddy Over a year ago

How do I add a new set to the array?

eerorika Over a year ago

@reddy Nothing can be added into an array. An array is initialised with the elements that it will have.

drescherjm Over a year ago

Using std::vector<data> instead of the array that has a fixed size at compile time can solve that.

reddy Over a year ago

What other container can I use that it can start out empty and I can add new set to it?

reddy Over a year ago

@drescherjm Okay I got it, this looks the easiest for me, thank you guys.

Vlad from Moscow · Accepted Answer · 2020-06-17 14:33:26Z

Use the class template std::tuple declared in the header <tuple>. For example

#include <iostream>
#include <string>
#include <tuple>

int main() 
{
    std::tuple<std::string, int, double> t ={ "John", 12, 40.025 };

    std::cout << std::get<0>( t ) << ", "
              << std::get<1>( t ) << ", "
              << std::get<2>( t ) << '\n';

    std::cout << std::get<std::string>( t ) << ", "
              << std::get<int>( t ) << ", "
              << std::get<double>( t ) << '\n';

    return 0;
}

The program output is

John, 12, 40.025
John, 12, 40.025

And you may use a container of elements with this type as for example an array because the listed types in the tuple are default constructible.

For example

#include <iostream>
#include <string>
#include <tuple>

int main() 
{
    std::tuple<std::string, int, double> t[1];

    t[0] = { "John", 12, 40.025 };

    std::cout << std::get<0>( t[0] ) << ", "
              << std::get<1>( t[0] ) << ", "
              << std::get<2>( t[0] ) << '\n';

    std::cout << std::get<std::string>( t[0] ) << ", "
              << std::get<int>( t[0] ) << ", "
              << std::get<double>( t[0] ) << '\n';

    return 0;
}

As an alternative you can define your own compound type (class or structure) that will contain sub-objects of required types.

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