Create std::set with keys of a std::map

Hi,

title says it all. Is there an easy way to create a set that contains the keys of my map? Background is, that one module of my program (a parser) needs the keys but I don't want to make the class that forms the second object of my map known to this module.

You could use something like:

Code:

---

#include <string>
#include <map>
#include <set>
#include <algorithm>


template <class MapType>
const typename MapType::key_type& GetMapKey( typename MapType::value_type& entry )
{
  return entry.first;
}

int main()
{
  typedef std::map<std::string,int> TestMap;
  TestMap testMap;

  testMap.insert( TestMap::value_type("A",1) );
  testMap.insert( TestMap::value_type("B",2) );
  testMap.insert( TestMap::value_type("C",3) );
  testMap.insert( TestMap::value_type("D",4) );

  std::set<TestMap::key_type> testSet;

  std::transform( testMap.begin(), testMap.end(), std::inserter(testSet,testSet.end()), GetMapKey<TestMap> );

  return 0;
}

---

The std::transform() inserts each key of the map into the set, using the templated function GetMapKey() to extract the key from the map entries.

one solution is pointer. you will better manage memory.

Kuphryn