Call Library Node; enum structure

[PJS]

I suspect that I already know the answer to this.  But is it possible to pass in the following defined structure to the call library node from labview:

struct HStradisDecoder {
    unsigned long hHandle;
};
typedef struct HStradisDecoder* STRADISDECODER;


Thoughts and Ideas?
Using LabVIEW 8.0+

[GuenterMueller]

Hi Paul,
in this special case the struct only contains one element of the data type unsigned.
If the DLL expects the struct by pointer you can pass from LabVIEW a pointer to a U32.
Regards, Guenter

[tbd]

Hi Paul,

In case you're interested, it's possible - even commonplace, when using the "Windows API" from LabVIEW - to represent and pass C-structures as LabVIEW arrays.  The DLL gets an "Array Data pointer" but assumes it's a "structure" pointer.  Constructing an array-representation of a stru of multiple elements and/or mixed-types can open the door to byte-padding problems.  I've never passed "really complex" strus and, in my expereince, byte-padding problems rare.

Cheers!

[PJS]

I am interested.  I tried passing a pointer to the U32 handle.  That did not work.  I tried a few other things.  As for the array?  I am not sure what you mean, simply convert the U32 as what?  a 4 byte array?  the dll in question has 650+functions.  I really do not want to wrap it. 

[tbd]

Hi Paul,

First I'd get Guenter's suggestion working - it should work! (and would make the parameter-passing very simple.)

Without knowing anything about the larger application it's difficult to guess why it didn't work.  Is the hHandle the correct value?  Does the "endian-ness" of hHandle change from caller (LabVIEW) to callee (DLL)?  - it might be necessary to reverse the byte-order of the U32/hHandle.

Attached is an example of a VI that calls a WinAPI (User32.dll) function.  The last two parameters to the DLL are non-trivial structures - passed and unpacked as arrays!

I stuffed the diagram with lots of prototypes, descriptions and links from MSDN - enjoy.

Cheers!

Message Edited by tbd on 08-16-2007 01:30 AM

[PJS]

If I was not frustrated this would have been funny.  The whole problem was that I was initializing the pointer with the DLL in the SDK directory and trying to call functions on the hardware using the DLL in the System32 directory. 
I appreciate the assistance, and the launcher.vi.  That information will come in handy with some of the more complex structures that I need to build for this hardware.

[tbd]

Enjoyed this - in a "happy-it-wasn't-me-this-time" sort of way!  

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@Stradis wrote:
If I was not frustrated this would have been funny.  The whole problem was that I was initializing the pointer with the DLL in the SDK directory and trying to call functions on the hardware using the DLL in the System32 directory. 

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Cheers!