Subject: Last byte of a file

90. *****
 Q: How can I quickly read the last byte of a file?

 A: Below is the code for a relevant procedure. It has a number of
instructive details for you to look into. It is easy to expand this
procedure into showing any byte counted from the end by substituting
the 1 in Seek (f, fs-1) to the inverted position, and by taking care
that the position is not outside the file.
  procedure LASTBYTE (fname  : string; var lb : byte);
  var f      : file;       { Use an untyped file designation }
      fmSave : byte;       { To push and pop the FileMode }
      fs     : longint;    { For file size }
  begin
    fmSave := FileMode;    { Push the original FileMode }
    FileMode := 0;         { To enable reading also read-only files }
    Assign (f, fname);
    {$I-} Reset (f, 1); {$I+}     { Open file and set record size to 1 }
    if IOResult <> 0 then begin
      writeln ('Error opening file ', fname);
      halt;
    end;
    fs := FileSize(f);     { Get the size of the file }
    if fs = 0 then begin
      writeln ('Empty file ', fname);
      halt;
    end;
    Seek (f, fs-1);        { Position to the last byte of the file }
    BlockRead (f, lb, 1);  { Read the value of the position into lb }
    Close (f);             { Close the file }
    FileMode := fmSave;    { Pop the original FileMode }
  end; (* lastbyte *)
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