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';
}