Re: stl map key

From:
"Azja" <azja@yahoo.com>
Newsgroups:
microsoft.public.vc.language
Date:
Thu, 11 May 2006 13:05:08 -0400
Message-ID:
<OkK7P0RdGHA.636@TK2MSFTNGP05.phx.gbl>
Hi,
Very nice Template, just tried it and works great.
I understand it finds first accurance in case there are more
then one same value for different key.
thanks a lot

"Stefan N?we" <stefan_NOSPAM@NOSPAM_naewe.de> wrote in message
news:e3vm0a$9er$1@news1.ewetel.de...

andre wrote:

Hi,
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
like that.
But I need to find a key for a given value.
thanks


This sohould do it:

//--------------------------------------
#include <iostream>
#include <map>
#include <utility>
#include <string>

template<typename T1, typename T2>
struct BySecond
{
   BySecond(const T2& t): t_(t)
       {
       }

   bool operator()(const std::pair<T1, T2>& p) const
   {
        return p.second == t_;
   }
private:

   T2 t_;
};

int main()
{
   std::map<int, std::string> m;

   m[0] = "Null";
   m[1] = "Eins";
   m[2] = "Zwei";

   std::map<int, std::string>::iterator it =
       find_if(m.begin(), m.end(), BySecond<int, std::string>("Zwei"));

   if (it!= m.end())
       std::cout << "Found it: " << it->first << " : " << it->second <<
std::endl;

   return 0;
}
//--------------------------------------

HTH
 Stefan
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