In which header file c++ STL hash function object is declared?

Question

If I want to use the hash function object provided in STL, which header file I should include on Linux? e.g. hash Hf;

Answer 1

#include <hash_map>

on some Linux distros it's available here:

#include <ext/hash_map>

More info here. The hash_map is currently not part of the official STL but it's in TR1 as <unordered_map>.

Answer 2

Is this what you are looking for:

Definition Defined in the headers hash_map and hash_set, and in the backward-compatibility headers hash_map.h and hash_set.h. This class is an SGI extension; it is not part of the C++ standard.

http://www.sgi.com/tech/stl/hash.html

Answer 3

And if you like reading standards proposals, here's a copy of Matt Austern's, A Proposal to Add Hash Tables to the Standard Library.