Description

   The ftell function measures the byte offset from the beginning of
   the file.

   For variable-length files, VFC files, or any file with carriage-
   control attributes, if the file is opened in record mode, then
   ftell returns the starting position of the current record, not
   the current byte offset.

   When using record files, the ftell function ignores any
   characters that have been pushed back using either ungetc or
   ungetwc. This behavior does not occur if stream files are being
   used.

   For a portable way to measure the exact offset for any type of
   file, see the fgetpos function.