How do I pass a 1D LabView array as a pointer to an array in a C DLL?

Hello,
I am trying to pass a 1D Labview array of DOUBLE to a C DLL which is expecting a pointer to an array of DOUBLE. I have read that LabView stores arrays as a pointer to a pointer and that the first element of a LabView array is actually the size of the array. So I think my question is then how do I dereference the first pointer and pass in a pointer which points to the second element in the array?
Any thoughts out there?
Thanks!

Hi justyou,
There are many, many resources on this topic, so I will guide you to the two most useful ones:
The "Call DLL.vi" example that ships with LabVIEW explains how to use almost any data type when executing DLLs. The "Call DLL.vi" can be found by browsing the Example Finder.
Integrating DLLs. This page is the portal for DLL interation related resources. Read the tutorials and try the examples...
This should give you some ideas.
Have fun!
- Philip Courtois, Thinkbot Solutions

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Hi,
Have you tried passing a I32, but selecting "Pointer To Value"?
Is there any description about the "void *pointer"? Could it be a callback
function?
Regards,
Wiebe.
"JoeLabView" wrote in message
news:[email protected]..
> I did read previous posts on the matter and tried just about
> everything, inlcuding defining the pointer as a U32 int.
>
> What I am trying to do is program FLASH using WindRiver VisionPROBE
> EST...
>
> I do have some sucesses... )
> I can open a connection to the EST, initialize it, start & stop the
> target. No problem here..
>
> Here are some additional details:
>
>
>
>
> I can't read memory, write to the target register or program the
> FLASH, yet. Any advice on how to get f
urther with this? Typically,
> when doing this using WR's visionClick sw, we need to use a register
> file which sets up the target. I have not seen any reference to this
> in their API.
>
> I can convert to CVI if necessary. I am using the dll's from
> WindRiver. I'd prefer keeping everything in LV, but LW-CVI is fine.
>
> My problem is that I am not sure if I am passing void pointers back &
> forth correctly. For instance, I need to call a function which
> returns a status, as follows:
>
>
> status = EST_WriteTargetRegister (long handle, Unsign int register,
> void * value)
>
>
> How do I pass the "void * value" to the input of a Call Library
> FUnction Node. I did try "Adapt to type" which does give a "void *
> value", and I tried both "Handles by Value" & "Pointers to Handles".
>
> When I change the input value to anything other than "Adpapt To Type",
> I get a violation error. >(
>
> Has anyone successfully automated WindRiver's EST?
>
> - Thanks -
>
> JLV"

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Part 1: I must confess that I don't understand your question. Pointers and arrays are very closely related in C so I'm not following the sequence. So I don't know if the following applies, but here is a possible answer...
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* If you want LV to convert your pointer to a LV data type (such as a LV array): Take a look at page 2-4 in the "Using External Code in LabVIEW". In almost all cases we do not support pointers. The only exceptions are the ones shown in the Call Library Node configuration. For arrays, notice that if you want to return an array to LV, we have our own defined data types for this - read up on the CIN section for more information.
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Did this help?
Message Edited by Lycangeek on 08-10-2005 02:12 PM
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Can you explain me the difference between LabView arrays and C arrays more detailed.
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Why I can't put an array inside a cluster
I didn't mean to imply that you can't do that. You can. LabVIEW will handle it correctly. But you can't pass the cluster to C and have it understood, using ordinary C array declarations.
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Solved!
Go to Solution.

Gerd,
thank you for the quick response and the easy solution.
Look what I did in the meantime. I solved the problem too, but muuuch more complicate :-)
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Johannes
Message Edited by johanneshoer on 04-28-2009 10:39 AM
Greetings Johannes
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