Beginning with OpenVMS Version 7.0, the DEC C RTL changed its date /time support model from one based on local time to one based on Universal Coordinated Time (UTC). This allows the DEC C RTL to implement ANSI C/POSIX functionality that previously could not be implemented. A UTC time-based model also makes the DEC C RTL compatible with the behavior of the Digital UNIX and OpenVMS POSIX RTL time functions.
By default, newly compiled programs will generate entry points into UTC-based date/time routines.
For compatibility with OpenVMS systems prior to Version 7.0, previously compiled programs that relink on an OpenVMS Version 7.0 system will retain local-time-based date/time support. Relinking alone will not access UTC support.
Compiling programs with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined will also enable local-time-based entry points. That is, the new OpenVMS Version 7.0 date/time functions will not be enabled.
Functions with both UTC-based and local-time-based entry points are:
ctime mktime fstat stat ftime strftime gmtime time localtime wcsftime