[Mono-dev] Marshalling (Segmentation fault)

[Abir Bhattacharya]

You cannot have a fixed IntPtr.


-----Original Message-----
From: russell.kay at realtimeworlds.com [mailto:russell.kay at realtimeworlds.com]

Sent: Thursday, October 11, 2007 4:50 PM
To: abirb at 2pirad.com; robertj at gmx.net; mono-devel-list at lists.ximian.com
Subject: RE: [Mono-dev] Marshalling (Segmentation fault)

The C# version of this Structure would be best expressed as

[StructLayout(LayoutKind.Explicit)]
unsafe struct FrameGrab
{
	[FieldOffset(0)]
	public int bufferlength;
	[FieldOffset(4)]
	Public fixed IntPtr buffer[1000]
}

One question are you definitely wanting an array of 1000 pointers.... if
it is really 1000 bytes you are wanting then it would look like

[StructLayout(LayoutKind.Explicit)]
unsafe struct FrameGrab
{
	[FieldOffset(0)]
	public int bufferlength;
	[FieldOffset(4)]
	Public fixed byte buffer[1000]
}

Accessing this array on the C# side would then be through a bit of
unsafe code

Public void DoSomething( IntPtr _pValFromCPP )
{
unsafe {
	fixed( FrameGrab* pFG = (FrameGrab*)_pValFromCPP.ToPointer()) {
		IntPtr p = pFG->buffer[0];
	// or
		Byte b = pFG->buffer[0];
	}
}
}

Russell

-----Original Message-----
From: mono-devel-list-bounces at lists.ximian.com
[mailto:mono-devel-list-bounces at lists.ximian.com] On Behalf Of Abir
Bhattacharya
Sent: 11 October 2007 12:09
To: 'Robert Jordan'; mono-devel-list at lists.ximian.com
Subject: Re: [Mono-dev] Marshalling (Segmentation fault)

The 'C' prototype :



#ifndef PICTURE_H
#define PICTURE_H

#include "def.h"


struct fgrab {
	int bufferlength;
	unsigned char *buffer[1000];
} typedef fgrab_struct;


fgrab_struct fbuffergrab();
void fbufferflush(fgrab_struct fgbuffer);

#endif

-----Original Message-----
From: mono-devel-list-bounces at lists.ximian.com
[mailto:mono-devel-list-bounces at lists.ximian.com] On Behalf Of Robert
Jordan
Sent: Thursday, October 11, 2007 4:32 PM
To: mono-devel-list at lists.ximian.com
Subject: Re: [Mono-dev] Marshalling (Segmentation fault)

Abir Bhattacharya wrote:
> 
> [DllImport ("lib.so")]
> 
> Private static extern ImgStruct gbuffergrab(); // gbuffergrab is the
'C'
> method which returns type struct

Please post the C prototype as well.

Robert

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