Re: stl map key

"Azja" <>
Thu, 11 May 2006 13:06:26 -0400
yes, I thought about this but it would be like extra step, which I wanted to
but thanks

"Hendrik Schober" <> wrote in message

andre <> wrote:

anybody can advise how to get a key from the map having value only?
The other way around its easy of course, and map is supposed to be used
But I need to find a key for a given value.

 I am aware that this doesn't exactly answer your question,
 but in case you find yourself doing this repeatedly and if
 you're sure that there's always a one-to-one relationship
 between keys and values, you might want to create a reversed
 map where keys and values are swapped.
 I have this in my toolbox:

   // Caution! I had to copy-paste this together from several
   // functions, so it might contain silly errors
   template< typename T1, typename T2 >
   inline void build_reverse_map(const std::map<T1,T2>& map,
std::map<T2,T1>& reverse_map)
     typedef std::map<T1,T2> map_type;
     typedef std::map<T2,T1> reverse_map_type;
     typedef typename reverse_map_type::value_type reverse_value_type;

     for( typename map_type::const_iterator it=map.begin(),
                                           end=map.end(); it!=end; ++it )
reverse_map.insert(reverse_value_type(it->second,it->first)).second );

 Use it like this:

   void f()
     std::map<int,string> my_map;
     // fill 'my_map'
     std::map<string,int> my_reverse_map;
     // use reverse map



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