Description

   The strsep function locates in stringp, the first occurrence of
   any character in delim (or the terminating '\0' character) and
   replaces it with a '\0'. The location of the next character after
   the delimiter character (or NULL, if the end of the string is
   reached) is stored in the stringp argument. The original value of
   the stringp argument is returned.

   You can detect an "empty" field; one caused by two adjacent
   delimiter characters, by comparing the location referenced by
   the pointer returned in the stringp argument to '\0'.

   The stringp argument is initially NULL, strsep returns NULL.