Marshalling Array In/Out C++ COM Control

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KidO - 09 Nov 2004 03:07 GMT

I have been researching this problem for some time, and I am hoping someone
here can help. I have more detailed code examples in a previous post
"Problem using ocx in VS.Net".

The COM obejct (OCX) I am trying to use has a method that accepts an array
and a size as input.

bool SimpleMethod(float* array, long* size)

When I use aximp on the control, it generates the wrapper dll, which using
ildasm shows the method as Simple Method(float32& array, int32& size)

When executed, the array is dimensioned to a max size, and the size is set.
The method fills the pre-created array, and the size reports the number of
actual elements in the array.

I have been pulling my hair out on this one. I have tried a number of
different changes in the wrapper with no luck. Any help is greatly
appreciated.

Thanks in advance...

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Mattias Sj?gren - 13 Nov 2004 01:17 GMT

You don't clearly state what the problem is, but I assume it's the
fact that the array parameter appears as a single ref parameter
instead of an array in managed code. If so, tyou can find the solution
at

http://msdn.microsoft.com/library/en-us/cpguide/html/cpconeditinginteropassembly.asp

in the exction "Conformant C-Style Arrays". Just make sure you specify
the [out] attribute as well since you're working with output
parameters.

Mattias

Signature

Mattias Sjögren [MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

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KidO - 17 Nov 2004 14:54 GMT

Mattias,

Thank you for your response, and I hope you may still be watching this thread.

I have previously tried the code in the link you recommended, and have
created a number of variations, including fixing a pointer to the array,
using Marshal.AllocCoTaskMem to allocate memory for the array, etc.

When using the method described in the link
http://msdn.microsoft.com/library/en-us/cpguide/html/cpconeditinginteropassembly.asp
the method call fails and a System.Runtime.InteropServices.COMException
occurs in mscorlib.dll, with the Additional information: Type Mismatch.

When the method of the OCX returns succesfully (no error), only the first
value in the array is passed back. Even with the untouched interop assembly
generated by aximp, this is the case, although I can not use an array larger
than 4 items.

Using OLEView, the the method looks like:

VARIANT_BOOL DetectCode(long* codeArray, short* arraySize)

The orginal IL of the interop assembly generated by aximp looks like:

instance bool DetectCode(int32& codeArray, int16& arraySize) runtime managed
preservesig internalcall

When the method is called, codeArray is intialized, and contains all 0's.
arraySize is the number of elements in codeArray. If the method call is
succesful, it returns true, and codeArray contains a number of values up to
the size set in arraysize, and arraySize is the actual (useful) number of
elements in the array.

Thanks in advance for your help.

John

"Mattias Sjögren" wrote:

> You don't clearly state what the problem is, but I assume it's the
> fact that the array parameter appears as a single ref parameter
[quoted text clipped - 8 lines]
>
> Mattias

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MarkM - 13 Jan 2005 20:45 GMT

I am having this exact problem. Did you ever solve it? What is the solution?

Mark

> Mattias,
>
[quoted text clipped - 47 lines]
> >
> > Mattias

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Marshalling Array In/Out C++ COM Control

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