Truncates the file at the current file position.
procedure Truncate(var F);
Windows, Real, Protected
F is a file variable of any type. All records past F are deleted, and the current file position also becomes end-of-file (Eof(F) is True).
If not,I/O-checking is off, the IOResult function returns a nonzero value if an error occurs.
F must be open. Truncate does not work on text files.