what do you mean with MS-DOS names?
Dos was, is and will ever be able to have 8 characters before the dot and up to three after the dot.
If a filename is longer than 8 characters than the tilde ~ is used to abbreviate the name. The extension is always the same, in Dos as well as in Windows (any version).
If you cannot see the extension and need the extension to include in your prog, set Windows Explorer to show the extension...in Explorer click on TOOLS than FOLDER OPTION than VIEW and see that the HIDE FILE EXTENSIONS.... is unchecked.
If you have trouble in giving your prog the right direction, think about your directories as well, only old-DOS short names are accepted.