strftime(3c): Replace (char *)0 by NULL
manpage - manual pages
(char *)0 by
NULL here in the
strftime(3c) man page:
If format is (char *)0, then the locale's default format is used. For strftime() the default format is the same as %c; for cftime() and ascftime() the default format is the same as %+. cftime() and ascftime() first try to use the value of the environment variable CFTIME, and if that is undefined or empty, the default format is used.