boost::unordered_map support by gcc

Question

When unoreded_map support was added to gcc?

I'm using gcc 4.1.1 shipped with RHEL 5.3. It looks like unoreded_map is missing. Is there a way to add it manually?

Answer 1

gcc doesn't have boost::unordered_map — it is part of Boost. It has std::tr1::unordered_map. It is included at least since 4.0.

To use std::tr1::unordered_map, include this header:

#include <tr1/unordered_map>

The interface of boost::unordered_map and std::tr1::unordered_map should be similar since the latter is created from the former.

Answer 2

On older gcc versions, you could also use a hash_map, which might be "good enough".

#include <ext/hash_map> // Gnu gcc specific!
...

// allow the gnu hash_map to work on std::string
namespace __gnu_cxx {
   template<> struct hash< std::string > {
      size_t operator()(const std::string& s) const {
         return hash< const char* >()( s.c_str() );
      }
   }; /* gcc.gnu.org/ml/libstdc++/2002-04/msg00107.html */
}

// this is what we would love to have:
typedef __gnu_cxx::hash_map<std::string, int> Hash;
....

and later

Hash hash;
string this_string;

...

hash[ this_string ]++;

...

which I did use often and with success.

Regards

rbo