You can switch your socket in the non-blocking mode with basic_stream_socket::non_blocking_io(). Though asio should handle MSG_DONTWAIT as well.

BR, Dmitry

Hi Dimitry, that's right, but i need a blocking read and a non-blocking wirte. With basic_stream_socket::non_blocking_io() both, read and write are non-blocking. When i use C-functions read is blocking and write is non-blocking (when passing MSG_DONTWAIT). Best regards Stefan