XPLM_API int        XPLMInitialized(void);

Deprecated: This function returns 1 if X-Plane has properly initialized the plug-in system. If this routine returns 0, many XPLM functions will not work.

NOTE: because plugins are always called from within the XPLM, there is no need to check for initialization; it will always return 1. This routine is deprecated - you do not need to check it before continuing within your plugin.