c++ - g++ 4.8.2: could not convert from function pointer to std::function<> -

i'm trying write class takes, constructor parameter, factory function creates instance of same class on transformed version of input. trivial example, functor class takes int, prints it, , returns functor prints input's successor.

i'm getting errors of form

error: not convert 'foo' 'type(*)(int)' 'std::function<type(int)>' 

the seems arise factory functions passed constructors.

using function pointer instead of std::function<> works fine, hoping c++11 i'd able avoid function pointers.

here's example:

#include <functional> #include <iostream>  // std::function-returning-int param in ctor default value // works fine  class princ; // "print , increment"  using worker = std::function<int(int)>;  int foo(int i) {     std::cout << << std::endl;     return i+1; }  class princ {   public:     princ(int i, worker fn = foo) : i_(i), fn_(fn) {}     int operator()() { return fn_(i_); }   private:     int i_;     worker fn_; };  // std::function-returning-princ2 param in ctor default value // fails, @ least on g++ 4.8.2 --std=c++11  class princ2;  using factory = std::function<princ2(int)>; // use function ptrs (instead of std::function<>s) , works fine //typedef princ2 (*factory)(int);  princ2 bar(int);  class princ2 {   public:     princ2(int i, factory fn = bar) : i_(i), fn_(fn) {}     princ2 operator()() { return fn_(i_); }   private:     int i_;     factory fn_; };  princ2 bar(int i) {     std::cout << << std::endl;     return princ2(i+1);     // error: not convert 'bar' 'princ2 (*)(int) 'factory {aka std::function<princ2(int)>' }  int main() {     auto p1 = princ {1};     auto p2 = princ{p1()};     p2();      auto p3 = princ2 {1};     // error: not convert 'bar' 'princ2 (*)(int) 'factory {aka std::function<princ2(int)>'     auto p4 = p3();     p4();      return 0; } 

what doing wrong?

edit: thelink2012's suggestion try princ2(int i, factory fn = factory(bar)) works fine on "repro" above, fails on motivating example (github link; relevant code erdos.h:35-54 around parsestep , parsefunction). drawing board better repro....

the following part of code, part appears relevant compiler error you're asking about, compiles cleanly gcc 4.9.2 using -std=c++11 mode:

#include <functional> #include <iostream>  using worker = std::function<int(int)>;  int foo(int i) {     std::cout << << std::endl;     return i+1; }  class princ {   public:     princ(int i, worker fn = foo) : i_(i), fn_(fn) {}     int operator()() { return fn_(i_); }   private:     int i_;     worker fn_; }; 

most bug in older gcc you're using. upgrade more recent version of gcc.