How to throw an exception in TwinCAT - twincat

Question

When using object-oriented programming aspects with Beckhoff TwinCAT 3 I recently tried to implement some Assert-like function which should throw an exception in case a guard clause evaluates to false.
Something like this:
FUNCTION GuardI
VAR_INPUT
Condition : BOOL;
Format : T_MaxString;
Value : INT;
END_VAR
IF (NOT Condition) THEN
ADSLOGDINT(
msgCtrlMask := ADSLOG_MSGTYPE_ERROR OR ADSLOG_MSGTYPE_LOG,
msgFmtStr := Format,
dintArg := Value);
// throw exception here
END_IF
So - how would I have it throw an exception?

Answer 1

I don't think it is possible to throw an exception from a quick look at the documentation. Note that exception handling (__TRY, __CATCH) only works for TwinCAT >= 4024.0 and for 32-bit systems.

Answer 2

You can do this like:
Create a Function called ASSERT
FUNCTION ASSERT
VAR_INPUT
E: BOOL;
END_VAR
VAR
EXCEPTION_THROWN, PURR: INT;
END_VAR
// body
IF NOT E THEN
EXCEPTION_THROWN := 0 / PURR;
END_IF
END_FUNCTION
Once you do this it will throw an exception guaranteed by Beckhoff because of the division by zero you would invoke this function like this (be sure that your are within the scope of that function via namespace or library reference):
PROGRAM MAIN
VAR
MEOW: INT; // zero by default
CONDITION: BOOL; // false by default
END_VAR
// body
IF MEOW = 1 THEN
ASSERT(FALSE);
END_IF
// ...
ASSERT(CONDITION); // key off your condition true or false
END_PROGRAM
Once you set "MEOW" to "1" or your condition evaluates to "FALSE" This will produce a Core Dump and you can load this core dump and review the call stack.
Hope this helps.