Know when data is sent

I believe know that call send or WSASend in nonblo开发者_JAVA技巧cking mode add simply data in a internal buffer, but how know when data is really sent ? My goal is to display a progress bar.

You could try Boost.Asio (if it's feasible for you to change). It can perform async or sync sending and receiving. When sending asyncronously you can register a function that will be called when the send is complete.