This function returns the amount of dataspace which has been set aside for the given file$. It is therefore similar to FDAT and FILE_DAT.
Default devices are not supported, however errors are not reported. The following error values may also be returned by the function:
-2: The file is not executable
-3 or -6: Insufficient memory to open file
-7: File does not exist
-9: Device or file is being written to by something else.
-12: The device is valid, but the filename is not
-16: Bad or changed medium error