Description

   The ctime and ctime_r functions convert the time pointed to by
   bintim into a 26-character string, and return a pointer to the
   string.

   The difference between the ctime_r and ctime functions is that
   the former puts its result into a user-specified buffer. The
   latter puts its result into thread-specific static memory
   allocated by the C RTL, which can be overwritten by
   subsequent calls to ctime or asctime; you must make a copy if
   you want to save it.

   On success, ctime returns a pointer to the string; ctime_r
   returns its second argument. On failure, these functions return
   the NULL pointer.

   The type time_t is defined in the <time.h> header file as
   follows:

   typedef long int time_t

   The ctime function behaves as if it called tzset.

                                  NOTE

      Generally speaking, UTC-based time functions can affect in-
      memory time-zone information, which is processwide data.
      However, if the system time zone remains the same during
      the execution of the application (which is the common case)
      and the cache of timezone files is enabled (which is the
      default), then the _r variant of the time functions asctime_
      r, ctime_r, gmtime_r, and localtime_r, is both thread-safe
      and AST-reentrant.

      If, however, the system time zone can change during the
      execution of the application or the cache of timezone files
      is not enabled, then both variants of the UTC-based time
      functions belong to the third class of functions, which are
      neither thread-safe nor AST-reentrant.