C++ Vector Find() Overloaded operator - Error -

i'm receiving undefined symbols architecture error when compiling this.

have use vector, find() algorithm, , non-member overloaded operator function.

some guidance around error appreciated.

  #include <stdio.h>   #include <iostream>   #include <stdexcept>   #include <vector>   #include <algorithm>   #include <string>    using namespace std;    struct person   {      char firstinitial;      string firstname;       person(const char fi, const string fn)      {         firstinitial = fi;         firstname = fn;      };       char getinitial()      {         return firstinitial;      };       string getname()      {         return firstname;      };       bool operator==(const person& r);    };    bool operator==(const person& r, const person& x)   {      return x.firstinitial == r.firstinitial;   }      int main (int argc, char *argv[])   {      vector<person> myvector;      vector<person>::iterator itr;       myvector.push_back(person('j', "john"));      myvector.push_back(person('s', "steve"));      myvector.push_back(person('c', "candice"));       itr = find (myvector.begin(), myvector.end(), person('s', ""));       if (itr != myvector.end())         cout << "first name: " << itr->getname() << '\n';      else         cout << "not found" << '\n';   } 

you need define comparator outside of class, not member function

class person {   public:     friend bool operator==(const person &a, const person &b); }  bool operator==(const person& r, const person& x) {      return x.firstinitial == r.firstinitial; } 

and should work, program returned "steve" me.