I am working at an OS independent file manager, in C. I managed to copy files, links and directories, but I am not sure how to copy devices. I would appreciate any help.
To create a device file, use the mknod(2) syscall. The struct stat structure will give you the major and minor device numbers for an existing device in st_rdev.
Having said that, there is little value in "copying" a device because a device doesn't contain anything useful. The major and minor numbers are specific to the OS on which they exist.