How do I store arrays in an STL list?

Question

Using C++ and the STL, does anybody know how to store integer arrays as nodes in an STL list or vector? I have an unknown number of pairs of numbers that I need to store, an

Answer 1

As of C++11, we can do this with the standard std::array:

#include <array>
#include <list>
#include <iostream>

int main () {
    std::list<std::array<int, 2>> l {{3,4},{5,6}};
    l.push_back({1,2});

    for (const auto &arr : l)
        for (const auto &v : arr)
            std::cout << v << ' ';
}

or

l.push_back({{1,2}});

etc. to silence some clang warning.

Output:

3 4 5 6 1 2 

Answer 2

With C++11 there is a ::std::array wrapper available which can be used with standard containers like this:

#include <array>
#include <iostream>
#include <list>
#include <cstdint>

int
main()
{
    using t_Buffer = ::std::array<::std::int32_t, 2>;
    using t_Buffers = ::std::list<t_Buffer>;
    t_Buffers buffers;
    buffers.emplace_back(t_Buffer{1, 2});
    ::std::cout << buffers.front()[0] << " " << buffers.front()[1] << ::std::endl;
    return(0);
}

Run this code online

Answer 3

You can't store arrays in STL containers. You'd use a vector of vectors or somesuch for the general case. For your specific case, I'd use a vector of std::pair, like so: std::vector<std::pair<int, int> >. std::pair is a class that has two members, first and second, of whatever type you templatize it to be.

Edit: I originally had it as std::vector<std::pair<int> >, but I wasn't sure if it was overloaded to accept only 1 parameter in the case that both types are the same... a little digging turned up no evidence of this, so I modified it to explicitly state that both first and second are ints.

Answer 4

I'd suggest you use std::pair to store the values in this case. It is located in
<utility>.

You could store pointers to the arrays in the list but then you would have to deal with all the memory management. Using pair is a lot simpler if pairs of values are all you need.

Answer 5

The thing stored in a Standard Library container must be assignable and copyable - arrays are neither. Your best bet is to create a list of std::vector. Alternatively, you can wrap the array in a struct:

struct A {
   int array[2];
};

std::list <A> alist;

Answer 6

This is a good situation for using boost::array instead of "classic" C-style arrays. This should work:

std::list<boost::array<int,2> > my_list;
boost::array<int,2> foo={{1,2}};
my_list.push_back(foo);