why does my functor member variable "reset" ? (c++) -

i learning how use functors, , created one, , don't understand why counter variable 0 @ end of programm.

here code:

#include"stdafx.h" #include<iostream> #include<vector> #include<algorithm> #include<map> #include<list>   using namespace std;  class myfunctor { public:     myfunctor():counter(0) {}     void operator()(int i) { cout << "in functor: " << ; counter++; cout << "   counter=" << counter << endl; }     int getcounter() const { return counter; } private:     int counter; };  int main() {     vector<int> v{ 1,2,3,4,5,6,7,8,9,10 };     myfunctor f;      for_each(v.begin(), v.end(), f);      cout << "counter=" << f.getcounter() << endl;      return 0; } 

here result gives:

in functor: 1   counter=1 in functor: 2   counter=2 in functor: 3   counter=3 in functor: 4   counter=4 in functor: 5   counter=5 in functor: 6   counter=6 in functor: 7   counter=7 in functor: 8   counter=8 in functor: 9   counter=9 in functor: 10   counter=10 counter=0 

if take @ signature for_each see accepts functor value, changes see inside for_each not reflected outside when algorithm terminates.

http://en.cppreference.com/w/cpp/algorithm/for_each

template< class inputit, class unaryfunction > unaryfunction for_each( inputit first, inputit last, unaryfunction f ); 

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if want make work going have use std::ref generate reference wrapper , pass value.

std::for_each(vec.begin(), vec.end(), std::ref(functor)); 

take @ documentation std::ref , reference_wrapper see how , why works (the key point std::reference_wrapper has operator() work functors http://en.cppreference.com/w/cpp/utility/functional/reference_wrapper/operator()).