Uhhh your on the wrong site. This site is about the Arduino.
though i doubt that there is a dedicated V720S-BC5D4A-vs.-C++ forum anywhere on the internet.
why does it have to be C++ from the start? just try to talk to the device using a serial port tool. select the port, speed and parity and send your commands. if the device (i have no experience with rfid-readers) does what you want it to do, you know that you're on the right way. the next thing to do would be finding a c++ forum, and (do a search first) ask there how to write commands to serial port.
still there might be simpler solutions (for you) using some scripting language instead of c++. since your talking about com ports, i guess you're asking for a windows program/skript. you might even try to your luck with the arduino serial proxy application + flash.
there are readymade solutions out there. just search for them.