The PtrIter class template implements an input iterator whose operator* returns the address of the element the iterator refers to. Consider a std::unordered_map<std::string, DataType>. Its begin member returns an iterator whose operator* returns a std::pair<std::string, DataType> (const) &. This is usually what you want, but now assume we want to display the map's content, sorted by its keys. Sorting can simply be performed by defining a support vector containing pointers to the elements in the map, and then sorting the strings the pointers point at.
PtrIter is a tool that can be used to construct such a support vector, as shown in the EXAMPLE section.
PtrIter is a class template requiring one template type parameter: Iterator, the iterator's type (e.g., vector<string>::iterator)
PtrIter's users don't have to specify PtrIter's template type. The function template ptrIter, when provided with an iterator returns the matching PtrIter object.
    PtrIter<set<string>::iterator> PtrIter(mySet.begin());
    
        Copy and move constructors (and assignment operators) are available.
#include <algorithm>
#include <unordered_map>
#include <vector>
#include <cstring>
#include <iostream>
#include <bobcat/ptriter>
using namespace std;
using namespace FBB;
int main()
{
    cout << "Enter lines, the first word will be the map's key; "
                                            "^D when done.\n";
    string key;
    string line;
    unordered_map<string, string> map;
    while (cin >> key && getline(cin, line))    // fill the map
        map[key] = line;
    cout << '\n';
                                        // initialize a support
    vector<decltype(&*map.begin())>     // vector, using ptrIter
        support(ptrIter(map.begin()), ptrIter(map.end()));
                                        // sort 'support'
    typedef unordered_map<string, string>::value_type VT;
    sort(support.begin(), support.end(),
        [&](VT const *p1, VT const *p2)
        {
            return strcasecmp(p1->first.c_str(), p2->first.c_str()) < 0;
        }
    );
    for(auto &element: support)         // display sorted by key
        cout << element->first << ' ' << element->second << '\n';
}