Futurebasic/Language/Reference/filesstring function
FILES$ edit
Function edit
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Syntax edit
fileType$ = FILES$
Description edit
Returns the file type of the last file returned by the FILES$(_fOpen...) function, as a 4-character string. If the user clicked "cancel" in response to the last File Open dialog, or if the FILES$(_fOpen...) function has never yet been executed, then the FILES$ function returns an empty (zero-length) string.
Note:
In some cases it's useful to express the file type as a 4-byte long integer rather than as a string. Use the MKI$ function and the CVI function to convert between these two forms.