Testing the validity of a reference

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.