[Boost-users] understanding placeholders

Subject: [Boost-users] understanding placeholders
From: Ozgur Ozturk (ozgur7_at_[hidden])
Date: 2009-07-12 20:34:44

Hi,
     I see in the code some functions are passed
things like boost::asio::placeholders::bytes_transferred.
But I didn't understand what is going on, what are their aim?

I found they are defined in placeholders.hpp as

boost::arg<2>& bytes_transferred
    = boost::asio::placeholders::detail::placeholder<2>::get();

//and the get function as
  template <int Number>
  struct placeholder
  {
    static boost::arg<Number>& get()
    {
      static boost::arg<Number> result;
      return result;
    }
  };

TIA,
Best regards,
Ozgur (Oscar) Ozturk
www.DrOzgur.com
[phone]