How to retrieve all keys (or values) from a std::map?
- by Owen
This is one of the possible ways I come out:
struct RetrieveKey
{
template <typename T>
typename T::first_type operator()(T keyValuePair) const
{
return keyValuePair.first;
}
};
map<int, int> m;
vector<int> keys;
// Retrieve all keys
transform(m.begin(), m.end(), back_inserter(keys), RetrieveKey());
// Dump all keys
copy(keys.begin(), keys.end(), ostream_iterator<int>(cout, "\n"));
Of course, we can also retrieve all values from the map by defining another functor RetrieveValues.
Is there any other way to achieve this easily? (I'm always wondering why std::map does not include a member function for us to do so.)
