Querying for failures in C and XML gauges

The Flight Simulator SDK describes a method of using FAILURE_RECORDS to fail gauge elements via an enumerated list of failure types (freeze, zero, and no_draw). See the "Programming C Gauges" section of the SDK for detailed information.

But what if you're creating a C gauge and want to implement some other sort of behavior in the case of a failure? A gauge programmer can programmatically query whether or not a system has failed using a collection of TOKEN_VARIABLES. The "Token Variables" document in the SDK lists them, but if you didn't know they were there, they can be easy to miss.

"PP" stands for "Partial Panel", a term used to describe the situation of flying without a complete set of instruments.

The following table lists the equivalent GAUGE_TOKENS and Simulation variables (for use in gauge XML or Modeldef.xml animation tags)

FAILURE_RECORD enum	GAUGE_TOKEN	XML A: variable
FAIL_SYSTEM_ENGINE	PP_ENGINE	PARTIAL PANEL ENGINE (will only get the state of engine #1) or ENG FAILED:1, ENG FAILED:2, etc. for each engine.
FAIL_SYSTEM_PITOT_STATIC	PP_PITOT	PARTIAL PANEL PITOT
FAIL_SYSTEM_VACUUM	PP_VACUUM	PARTIAL PANEL VACUUM
FAIL_GAUGE_ADF	PP_ADF	PARTIAL PANEL ADF
FAIL_GAUGE_AIRSPEED	PP_AIR	PARTIAL PANEL AIRSPEED
FAIL_GAUGE_ALTIMETER	PP_ALTIM	PARTIAL PANEL ALTIMETER
FAIL_GAUGE_ATTITUDE	PP_ATTITUDE	PARTIAL PANEL ATTITUDE
FAIL_GAUGE_COMMUNICATIONS	PP_COM	PARTIAL PANEL COMM
FAIL_GAUGE_FUEL_INDICATORS	PP_FUEL_IND	PARTIAL PANEL FUEL INDICATOR
FAIL_GAUGE_GYRO_HEADING	PP_HEADING	PARTIAL PANEL HEADING
FAIL_GAUGE_MAGNETIC_COMPASS	PP_COMPASS	PARTIAL PANEL COMPASS
FAIL_GAUGE_NAVIGATION_VOR1	PP_NAV	PARTIAL PANEL NAV:1
FAIL_GAUGE_NAVIGATION_VOR2		PARTIAL PANEL NAV:2
FAIL_GAUGE_TRANSPONDER	PP_XPNDR	PARTIAL PANEL TRANSPONDER
FAIL_GAUGE_TURN_COORDINATOR	PP_TURN_COORD	PARTIAL PANEL TURN COORDINATOR
FAIL_GAUGE_VERTICAL_SPEED	PP_VERT_VEL	PARTIAL PANEL VERTICAL VELOCITY
FAIL_SYSTEM_ELECTRICAL_PANELS	PP_ELECT	PARTIAL PANEL ELECTRICAL
FAIL_SYSTEM_ELECTRICAL_AVIONICS		PARTIAL PANEL AVIONICS
FAIL_GAUGE_COMMUNICATIONS_COM2		PARTIAL PANEL COMM:2