read and write data in c on windows xp to allready open com1

Hi, Im working in a console apllication in codeblocks under windows xp and I basically need 2 functions to read and write to an all ready open com1 port. The com port is being used by another apllication, However I want to be able to read and write to it transparantly regardless of it being allready open by another application. So if i want to write a packet, I need a function to call to send the data. And secondaly i need a function that I poll to see if there is any data recieved. If I read any data, I dont want it to go missing from the first apllication that opened the com port. ie be transparant.