Problem:
If I have a .Net class and I was to pass a null reference to it from Unmanaged COBOL. How can I do it ?
This is going via .Net COM Interop.
Resolution:
To get this worked as expected you need to pass a COM Variant object with the type set to DISP-E-PARAMNOTFOUND.
This denotes to COM that it is a missing parameters and the .Net Class is given a null object.
The COBOL code to do this is:-
invoke oleVariant "new" returning mynull
invoke mynull "getVariantAddress" returning ws-ptr
set address of lnk-var to ws-ptr
move DISP-E-PARAMNOTFOUND
to VARIANT-VT-SCODE of lnk-var
invoke ws-dnobj "TestMethod"
using by reference string1
by reference mynull
by value inta
by value intb
returning retval
Attached to this article is a working example showing how to do this.
You will need to run "regasm /tlb /codebase TestCOBOLNull.dll" on the .Net assembly to register it for COM Interop.
