C でフラット化イテレータを作成してネストされたコンテナを反復処理するにはどうすればよいですか?

#include <algorithm>
#include <iostream>
#include <set>
#include <vector>

template <typename OuterIterator>
class flattening_iterator
{
public:
    // ... Iterator definitions and implementation

private:
    void advance_past_empty_inner_containers()
    {
        // ... Advance logic
    }

    // ... Private members
};

template <typename Iterator>
flattening_iterator<Iterator> flatten(Iterator it)
{
    // ... Return a flattening iterator for a single range
}

template <typename Iterator>
flattening_iterator<Iterator> flatten(Iterator first, Iterator last)
{
    // ... Return a flattening iterator for a range
}

// Generate some test data
std::vector<std::vector<int>> v(3);
int i(0);
for (auto it(v.begin()); it != v.end(); ++it)
{
    it->push_back(i++);
    it->push_back(i++);
    it->push_back(i++);
    it->push_back(i++);
}

// Flatten the data and print all the elements
for (auto it(flatten(v.begin(), v.end())); it != flatten(v.end()); ++it)
{
    std::cout << *it << ", ";
}