Unmanaged C++ Void*

[Frustrated]

I have a C++ DLL that I need to access from VB.NET. The function I am
trying to call is declared like this:

void* PASCAL iidc_lockdata( HIIDC, long frame = -1 )

This function returns a pointer to unsigned chars

I am able to find the size of the array out. It is usually 128800 to
use as an example if it helps.

I have declared the interface for my VB.NET as follows:

Private Declare Function _iidc_lockdata Lib "iidcapi_SONY.d ll" Alias
"#37" (ByVal HIIDC As Int32, ByVal frame As Int32) As
System.Runtime. InteropServices .GCHandle

and also I have tried it as

Private Declare Function _iidc_lockdata Lib "iidcapi_SONY.d ll" Alias
"#37" (ByVal HIIDC As Int32, ByVal frame As Int32) As IntPtr

(1) My first question is, how do I declare the function, should I use
GCHandle or IntPtr or something else?

As far as calling the function goes, I have tried this:

Dim gch As System.Runtime. InteropServices .GCHandle
gch = New System.Runtime. InteropServices .GCHandle
Dim lBufSz As Int32 = camera.currentD ataFrameBytes(m _hCamera)
gch.Alloc(lBufS z)
Try
gch = camera.lockdata (m_hCamera, -1)
gch.Free()
Catch ex As Exception
MsgBox(ex.Messa ge)
End Try

FYI the function camera.lockdata is a mapped function and it is as
follows:

Public Function lockdata(ByVal HIIDC As Int32, ByVal frame As Int32)
As System.Runtime. InteropServices .GCHandle
Return _iidc_lockdata( HIIDC, frame)
End Function


and I get "Object reference not set to an instance of an object"

(2) How would I get the data?

I have been really struggling with this.

Thanks,
Mike Dixon

[Mattias Sjögren]

Re: Unmanaged C++ Void*

Mike,
[color=blue]
>(1) My first question is, how do I declare the function, should I use
>GCHandle or IntPtr or something else?[/color]

IntPtr

[color=blue]
>(2) How would I get the data?[/color]

System.Runtime. InteropServices .Marshal.Copy



Mattias

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

[Ken Tucker [MVP]]

RE: Unmanaged C++ Void*

Hi,

The function should return an intptr. You should be able to use
marshal.ptrtost ructure or one of the marshal.pointer tostring function to get
the data.

http://msdn2.microsoft.com/en-us/lib...l_members.aspx

Ken
---------------

"Frustrated " wrote:
[color=blue]
> I have a C++ DLL that I need to access from VB.NET. The function I am
> trying to call is declared like this:
>
> void* PASCAL iidc_lockdata( HIIDC, long frame = -1 )
>
> This function returns a pointer to unsigned chars
>
> I am able to find the size of the array out. It is usually 128800 to
> use as an example if it helps.
>
> I have declared the interface for my VB.NET as follows:
>
> Private Declare Function _iidc_lockdata Lib "iidcapi_SONY.d ll" Alias
> "#37" (ByVal HIIDC As Int32, ByVal frame As Int32) As
> System.Runtime. InteropServices .GCHandle
>
> and also I have tried it as
>
> Private Declare Function _iidc_lockdata Lib "iidcapi_SONY.d ll" Alias
> "#37" (ByVal HIIDC As Int32, ByVal frame As Int32) As IntPtr
>
> (1) My first question is, how do I declare the function, should I use
> GCHandle or IntPtr or something else?
>
> As far as calling the function goes, I have tried this:
>
> Dim gch As System.Runtime. InteropServices .GCHandle
> gch = New System.Runtime. InteropServices .GCHandle
> Dim lBufSz As Int32 = camera.currentD ataFrameBytes(m _hCamera)
> gch.Alloc(lBufS z)
> Try
> gch = camera.lockdata (m_hCamera, -1)
> gch.Free()
> Catch ex As Exception
> MsgBox(ex.Messa ge)
> End Try
>
> FYI the function camera.lockdata is a mapped function and it is as
> follows:
>
> Public Function lockdata(ByVal HIIDC As Int32, ByVal frame As Int32)
> As System.Runtime. InteropServices .GCHandle
> Return _iidc_lockdata( HIIDC, frame)
> End Function
>
>
> and I get "Object reference not set to an instance of an object"
>
> (2) How would I get the data?
>
> I have been really struggling with this.
>
> Thanks,
> Mike Dixon
>
>[/color]