CL accepts files with names that follow FAT, HPFS, or NTFS naming conventions. Any filename can include a full or partial path. A full path includes a drive name and one or more directory names. CL accepts filenames separated either by backslashes (\) or forward slashes (/). A partial path omits the drive name, which CL assumes to be the current drive. If you don’t specify a path, CL assumes the file is in the current directory.
The filename extension determines how files are processed. C and C++ files, which have the extension .C, .CXX, or .CPP, are compiled. Other files, including .OBJ files, libraries (.LIB), and module-definition (.DEF) files, are passed to the linker without being processed.