Description

   The truncate function changes the length of a file to the size,
   in bytes, specified by the length argument.

   If the new length is less than the previous length, the function
   removes all data beyond length bytes from the specified file. All
   file data between the new End-of-File and the previous End-of-
   File is discarded.

   For stream files, if the new length is greater than the previous
   length, new file data between the previous End-of-File and the
   new End-of-File is added, consisting of all zeros. (For record
   files, it is not possible to extend the file in this manner.)