usb serial programming

[Amadeus W.M.]

Not sure if this is the right venue for this question, please direct me to
the right place if it's not.

I have a C program that opens the serial port /dev/ttyS0 and sends commands 
(as strings) back and forth to a pan-tilt-zoom camera. That works very well,
but I want to use the camera with a Raspberry Pi, which of course does not 
have a serial port (RS232). One option is to use a RS232 to usb adapter and 
rewrite the C code for the usb port. So how do I go about that? Is
usb serial port programming possible and documented anywhere? 

Thanks!