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Is this part of the STL? It's in some guides but not in others and I don't seem to have an implementation of it (in GNU C++). It sounds useful for the script parser I'm writing as I don't need the sorting capabilities of a map and performance is necessary.
hash_map is not a part of the standard library currently.
edit: though I believe STLPort has a hash_map version, if your copy of gcc doesn't ship with one.
edit: though I believe STLPort has a hash_map version, if your copy of gcc doesn't ship with one.
As mentioned hash_map is a standard library extension not part of the standard and is currently being reviewed to be incorporated into the standard under a new name unordered_map in the TR1 technical library review 1.
GCC does have hash_map but its in a different header in a different namespace than expectated.
GCC >= 4.0 its unordered_map in namespace std::tr1 in the header tr1/unordered_map i believe.
GCC < 4.0 && GCC >= 4.0 its hash_map in namespace __gnu_cxx in header ext/hash_map.
Note if you intend on using GCC hash_map's key type to be std::basic_string you either need to do a specialization for std::hash or provide a custom hasher type not sure if this is the case for GCC's imp of std::tr1::unordered_map.
[Edited by - snk_kid on July 8, 2005 1:44:53 PM]
GCC does have hash_map but its in a different header in a different namespace than expectated.
GCC >= 4.0 its unordered_map in namespace std::tr1 in the header tr1/unordered_map i believe.
GCC < 4.0 && GCC >= 4.0 its hash_map in namespace __gnu_cxx in header ext/hash_map.
Note if you intend on using GCC hash_map's key type to be std::basic_string you either need to do a specialization for std::hash or provide a custom hasher type not sure if this is the case for GCC's imp of std::tr1::unordered_map.
[Edited by - snk_kid on July 8, 2005 1:44:53 PM]
Quote:
Note if you intend on using GCC hash_map's key type to be std::basic_string you either need to do a specialization for std::hash or provide a custom hasher type...
An example of the specialization, since it's tricky, and pretty vital to using it effectively:
This should probably be in it's own header, so that inclusion guards, and portability stuff can be wrapped around it.
namespace __gnu_cxx{template <>struct hash<string>{ size_t operator()(const string &s) const { hash<const char *> h; return(h(s.c_str())); }};}
I've heard that there is a boost library implementing the TR1 functionality (including unordered_map) coming in the near future, but that could just be a rumour.
Also, std::map offers a very similar interface to unordered_map (just the hash function differs), so it's easy to just use std::map then switch if your profiling reveals that to be a bottleneck (which it could well do with medium-large amounts of data).
So you could use a typedef like:
typedef std::map<T1,T2> associative_container_T1_T2;
later to be replaced by
typedef std::unordered_map<T1,T2,hash_function_object> associative_container_T1_T2;
Also, std::map offers a very similar interface to unordered_map (just the hash function differs), so it's easy to just use std::map then switch if your profiling reveals that to be a bottleneck (which it could well do with medium-large amounts of data).
So you could use a typedef like:
typedef std::map<T1,T2> associative_container_T1_T2;
later to be replaced by
typedef std::unordered_map<T1,T2,hash_function_object> associative_container_T1_T2;
Quote:Original post by Telastyn
*** Source Snippet Removed ***
How about generalizing & internalization it [grin]:
#include <string>#include <locale>#include <ext/hash_map>namespace __gnu_cxx { template< typename CharT, typename Traits, typename Alloc > struct hash< const std::basic_string<CharT, Traits, Alloc> > { size_t operator()(const std::basic_string<CharT, Traits, Alloc>& s) const { const std::collate<CharT>& c = std::use_facet<std::collate<CharT> >(std::locale()); return c.hash(s.c_str(), s.c_str() + s.length()); } }; template< typename CharT, typename Traits, typename Alloc > struct hash< std::basic_string<CharT, Traits, Alloc> > : hash< const std::basic_string<CharT, Traits, Alloc> > {};};
I'm just happy I got those 9 lines of code working after 3-4 hours [I'm not so good at reading through others' code]. Thanks for the better version though :]
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