IO control command to get the amount of data that can be read without blocking.

typedef implementation_defined bytes_readable;

Implements the FIONREAD IO control command.

Example

boost::asio::ip::tcp::socket socket(io_service); 
...
boost::asio::socket_base::bytes_readable command(true);
socket.io_control(command);
std::size_t bytes_readable = command.get();