Compiler error C0239

Message: Interface <interface name 1> does not extend <interface name 2>

Possible error cause: The used interface does not extend another interface.

Error correction: Extend the interface.

Example of the error:

PROGRAM PLC_PRG
VAR
	ITFref : ITF;
	ITFref2 : ITF2;
END_VAR

__QueryInterface(ITFref2,ITFref);

INTERFACE ITF
INTERFACE ITF2 EXTENDS ITF

--> C0239: Interface ITF__Union does not extend __System.IQueryInterface

Error correction:

Example:
INTERFACE ITF EXTENDS __System.IQueryInterface