are there some function in C to notify about the OS used?

[Javier Matos]

I was programming an application to work with system process that can be found in /proc path and now I must to migrate my application to a linux OS but the structure of status file is different. I made two procedures to take information about status files, one for FreeBSD and another for Linux... , now I need some function in C to notify about the OS used to run the application to select between two procedures... but I can´t find it, can anyone help me?

Thanks