Compiler Error C0234

Message: First Operand of __QueryInterface must be an interface reference or the instance of a function block

Possible error cause: Incorrect operands are passed to the operator __QueryInterface.

Error correction: Pass an interface reference or the instance of a function block.

Example 452. Example of the error:

PROGRAM PLC_PRG
VAR
    a : INT;
    ITFref, ITFref2 : ITF;
    ITFref2 : ITF2;
END_VAR

__QueryInterface(a ,ITFref);

INTERFACE ITF EXTENDS __SYSTEM.IQueryInterface
INTERFACE ITF2 EXTENDS ITF

Message:

C0234: First Operand of __QueryInterface must be an interface reference or the instance of a function block

Error correction:

__QueryInterface(ITFref2, ITFref);