With POSIX IDs disabled, this function is equivalent to getuid
    and returns the member number (in OpenVMS terms) from the user
    identification code (UIC).

    With POSIX IDs enabled, this function returns the effective user
    ID.

    Format

      #include  <unistd.h>

      uid_t geteuid  (void);

  Additional Information (explode) :

• Description
• Return Value