VSI C defines the following macros that you can explicitly define (using the /DEFINE qualifier or the #define preprocessor directive) to control which VSI C RTL functions are declared in header files and to obtain standards conformance checking: _XOPEN_SOURCE_EXTENDED _XOPEN_SOURCE _POSIX_C_SOURCE _ANSI_C_SOURCE _VMS_V6_SOURCE _DECC_V4_SOURCE __BSD44_CURSES __VMS_CURSES _SOCKADDR_LEN