How to tell if a string to serial port has been sent

I have a need to determine when a string has been completely sent via a serial port from a standard 'C' application. The code is as follows:

SerialPort_Send = open \(pPortString, O_WRONLY | O_NOCTTY | O_NONBLOCK\);
write \(SerialPort_Send, pCommandString, strlen \(pCommandString\)\);
close \(SerialPort_Send\);

Is there a way of doing this?

Thanks in advance
-ExDes-

Then open the serial port in blocking mode so that it won't close until the entire string has been read by the receiving process.

Have the other side send back some kind of information (eg 0xFF or some other byte of your choosing) as soon as all information has been received.