Please use boost/bind/bind.hpp + using namespace boost::placeholders

The practice of declaring the Bind placeholders (_1, _2, …) in the global namespace is deprecated. Please use <boost/bind/bind.hpp> + using namespace boost::placeholders, or define BOOST_BIND_GLOBAL_PLACEHOLDERS to retain the current behavior.

• 提示warning的代码

#include <iostream>
#include <boost/bind.hpp>

using namespace std;
using namespace boost;

int fun(int x