"Reloading" a Boost Timer bind to a class method - c++

Question

I've got some trouble with the asio timer.
It is bind to a class method, and when I reload the timer (each time I'm waiting for data or ack), the call back method is called (according to the boost spec).
The problem is that I don't know how to differentiate the cancelation or the completion of the timer.
How should I do that ?
Thanks !
const int TIMER_DURATION = 5000; // ms
tftp_connection::tftp_connection (std::string id,
std::string file_name,
connection_type_enum connection_type,
tftp_server* server,
boost::asio::io_service& io_service)
: timer(io_service, boost::posix_time::milliseconds(TIMER_DURATION)) {
//...
// when sending a block and waiting for acknowledgement
timer.expires_from_now(boost::posix_time::milliseconds(TIMER_DURATION));
timer.async_wait(boost::bind(&tftp_connection::timeout_callback , this));
//...
void tftp_connection::timeout_callback() {
std::cout << "Time Out\n"; }

Answer 1

Looks like you want to check the error code that can be given to the callback if you use the right callback function type. Have a look at:
Boost async_wait example
Your callback should look somehow like this:
void tftp_connection::timeout_callback(const boost::system::error_code& e) {
if(e.value() == ERROR_TIMEOUT) // Or whatever error code you want to check for.
{
std::cout << "Time Out\n";
}
}
in addition, you need to change the bind to:
timer.async_wait(boost::bind(&tftp_connection::timeout_callback , this,boost::asio::placeholders::error));
The boost::asio::placeholders::error tells the bind to create a function which can use the error code as an argument.