Use the deffile field to specify a module-definition file when you are linking a segmented executable file, which is an application or DLL for OS/2 or Windows. A module-definition file is optional for an application but required for a DLL. If you specify a base name with no extension, LINK assumes a .DEF extension. If the filename has no extension, put a period (.) at the end of the name.
By default, LINK assumes that no deffile needs to be specified. If you are linking for DOS, use a semicolon to terminate the command line before the deffile field (or accept the default NUL.DEF at the Definitions File prompt).
LINK searches for the module-definition file in the following order:
1.The directory specified for the file (if a path is included). If the file is not in that directory, the search terminates.
2.The current directory.
For information on module-definition files, see Chapter 13.