The C RTL supports 32-bit User Identification (UID) and Group
    Identification (GID). When an application is compiled to use
    32-bit UID/GID, the UID and GID are derived from the UIC as in
    previous versions of the operating system.

    To compile an application for 16-bit UID/GID support on systems
    that by default use 32-bit UIDs/GIDs, define the _DECC_SHORT_GID_
    T macro to 1.

    Not specifying _DECC_SHORT_GID_T provides long (32-bit) UID/GID.

    Compiling on older OpenVMS systems where long UID/GID is not
    supported, or compiling for legacy compatibility (_DECC_V4_SOURCE
    for VSI C Version 4 or _VMS_V6_SOURCE for OpenVMS Version 6),
    forces use of short (16-bit) UID/GID.