What is the best way to take generically a container in C++ using interfaces (i.e. equivalent of taking IEnumerable as argument in C#)

Question

Hello, I would like a C++ constructor/method to be able to take any container as argument. In C# this would be easy by using IEnumerable, is there an equivalent in C++/STL ?

Anthony

Answer 1

The C++ way to do this is with iterators. Just like all the <algorithm> functions that take (it begin, it end, ) as first two parameters.

template <class IT>
T foo(IT first, IT last)
{
    return std::accumulate(first, last, T());
}

If you really want to go passing the container itself to the function, you have to use 'template template' parameters. This is due to the fact that C++ standard library containers are not only templated with the type of the contained type, but also with an allocator type, that have a default value and is therefore implicit and not known.

#include <vector>
#include <list>
#include <numeric>
#include <iostream>

template <class T, class A, template <class T, class A> class CONT>
T foo(CONT<T, A> &cont)
{
    return std::accumulate(cont.begin(), cont.end(), T());
}

int main()
{
    std::vector<int> v;
    v.push_back(1);
    v.push_back(2);
    v.push_back(3);

    std::list<int> l;
    l.push_back(1);
    l.push_back(2);
    l.push_back(3);

    std::cout << foo(v) << " " << foo(l) << "\n";

    return 0;
}

Answer 2

Depends what you want to do with the container. One thought: just pass an iterator if you want to access what is stored in the container.