Maybe this question have been answered already but could not find relevant information with search function in adaquate time.

How do I know wether to use invoke or cinvoke macro to call a DLL function ?
I think the MS DLL's are all compatible with the invoke macro but what about custom DLL's not designed by MS ? How can I obtain the calling procedure if not provided in documents ?

Concrete case is for this API
http://www.ftdichip.com/Support/Documents/ProgramGuides/D2XX_Programmer%27s_Guide%28FT_000071%29.pdf

But would be good to know in general for future / other provided API's.

Thanks for help.

By looking at FTD2XX.H in example 1 I'd say they are stdcall and therefore you must use invoke. The reason I think they are stdcall is because they are marked WINAPI (which is defined as __stdcall).

Yes, you use invoke. This is from my code:

Thanks for information.

But is there a general rule what macro to use under which circumstances (if documentation is not provided or not with that detail) ?

Yes.

cinvoke for ccall
invoke for stdcall Use a debugger and check the return type.

ret = ccall
ret imm = stdcall