Re: stl map key

"Azja" <>
Thu, 11 May 2006 13:05:08 -0400
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" <> 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
like that.
But I need to find a key for a given value.

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_;

   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 <<

   return 0;


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