Could not convert from brace initializer list to vector

Question

I'm observing compilation error "error: could not convert '{{{&Foo::print_add}, {&X::print}}}' from '' to 'std::vector'" in the below code.

Am I doing the vector insertion wrong? BTW I don't want to use push_back method. Is it possible to insert using '='. I'm having a feeling that it's syntactical mistake but not able to find it.

When googled, I found that there was a bug in earlier versions of gcc. I'm using 4.8.1 so I'm assuming the library I'm using should include the fix.

#include <functional>
#include <iostream>
#include <vector>

struct Foo {
  Foo(int num) : num_(num) {}
  void print_add(int i) const { std::cout << num_+i << '\n'; }
  int num_;
};

struct X {
  void print() {
    std::cout << "I'm in X "<<std::endl;
  }
};

struct XXX {
  std::function<void(const Foo&,int)> a;
  std::function<void(const X&)> b;
};

int main()
{
  std::vector<XXX> vec = 
  {  
     { 
        {&Foo::print_add},
        {&X::print}
    }
 };
}

Answer 1

X::print is a non-const member function, and therefore a pointer to it cannot be used to initialize a std::function<void(const X&)>.