c++ - For_each and pointer to member function -

i came across problem following code:

#include <list> #include <algorithm> #include <string> #include <iostream> #include <functional> using namespace std;  struct person {     string name;     ostream& print(ostream& out) const {         return out << name;     } };  int main() {     person p = { "mark" };     list<person> l;     l.push_back(p);     for_each(l.begin(), l.end(), bind(&person::print, std::placeholders::_1, std::cout)); // placeholder not pointer can't work anyways      // tried lambdas doesn't work either     //for_each(l.begin(), l.end(), bind([](person& p, ostream& out) { mem_fun(&person::print)(&p, out); }, std::placeholders::_1, cout));      // doesn't work way     //for_each(l.begin(), l.end(), bind([](person& p, ostream& out) { p.print(out); }, std::placeholders::_1, cout)); } 

here's error message (in every case)

microsoft visual studio 12.0\vc\include\tuple(80): error c2248: 'std::basic_ostream<char,std::char_traits<char>>::basic_ostream' : cannot access protected member declared in class 'std::basic_ostream<char,std::char_traits<char>>' 

i want know what's under hood , why doesn't work. protected member talking about?

your for_each call (and associated bind) trying copy std::cout (regardless print takes reference) impossible since streams non-copyable.

in c++03, way enforce non-copyability declare copy constructor protected (or private), hence error you're seeing.

pass std::ref(std::cout) instead.