You can use the operator __ISVALIDREF to check whether or not a reference points to a valid value (meaning a value not
equal to 0).
Syntax
<boolean variable name> := __ISVALIDREF( <reference name> );
<reference name>: Identifier declared with REFERENCE TO
The Boolean variable is TRUE when the reference points to a valid value. Otherwise it is FALSE.
Example
PROGRAM PLC_PRG
VAR
iAlfa : INT;
riBravo : REFERENCE TO INT;
riCharlie : REFERENCE TO INT;
bIsRef_Bravo : BOOL := FALSE;
bIsRef_Charlie : BOOL := FALSE;
END_VAR
iAlfa := iAlfa + 1;
riBravo REF= iAlfa;
riCharlie REF= 0;
bIsRef_Bravo := __ISVALIDREF(riBravo); (* becomes TRUE, because riBravo references to iAlfa, which is non-zero *)
bIsRef_Charlie := __ISVALIDREF(riCharlie); (* becomes FALSE, because riCharlie is set to 0 *)
In compiler version 3.5.7.40 and higher, the implicit monitoring function “CheckPointer” acts on variables of type REFERENCE TO in the same way as for pointer variables.