dotnet interop: dll access error c# pass array of null pointers to c function -- dotnet interop

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dll access error c# pass array of null pointers to c function

linknum23 NO[at]SPAM gmail.com
11/29/2006 8:44:31 AM

dotnet interop: Ive been trying to use the following function from the imaq.dll
library:
imgSequenceSetup(SESSION_ID sid, uInt32 numberOfBuffers, void*
bufferList[ ], uInt32 skipCount[ ], uInt32 startNow, uInt32 async);

Everything I've tried I've gotten the error "Attempted to read or write
protected memory. This is often an indication that other memory is
corrupt."

The problem seems to be that I do not pass the array of pointers
properly.
The documentation tells me that i can pass either an array of null
pointers to be allocated, of pass an array of pointers already
allocated.

Some different things ive tried:
1.
public void StartSequenceAquire(){
imgBufList = new IntPtr[10];

imgSequenceSetup(sessionId, 10, imgBufList, 0, 1, 1); << it fails
here
}

[DllImport("imaq.public extern static int imgSequenceSetup(int
SessionID, int NumberOfBuffers,
[In,Out,MarshalAs(UnmanagedType.LPArray, SizeParamIndex=1)] int[]
BufferList, int SkipCount, int StartNow, int Async);

2.
public void StartSequenceAquire(){
int numImages = 10;
IntPtr imgBufPtr = Marshal.AllocHGlobal(40800*numImages);
IntPtr imgBufAddListPtr = Marshal.AllocHGlobal(40 * numImages);
for (int ii = 0; ii < numImages; ii++)
{
Marshal.WriteInt32(imgBufAddListPtr,ii*4,imgBufPtr.ToInt32() +
4080 * ii);
}
imgSequenceSetup(sessionId, 10, imgBufAddListPtr, 0, 1, 1); <<- it
fails here, the method and its documentation are shown below
}

[DllImport("imaq.dll")]
public extern static int imgSequenceSetup(int SessionID, int
NumberOfBuffers, IntPtr BufferList, int SkipCount, int StartNow, int
Async);

3. Ive also tried several variations of the previous methods using ref
and repacing int with IntPtr and vice versa

documentation for the method is as follows:
pay special attention to the bufferlist parameter

/// <summary>
/// Prepares a session for acquiring a sequence into the buffer list.
/// </summary>
/// <param name="sid">valid SESSION_ID</param>
/// <param name="NumberOfBuffers">number of buffers in the buffer
list.</param>
/// <param name="bufferList">array of buffer pointers. For each element
in the buffer list that is initialized to NULL, bufferList[ ]
allocates a buffer and returns this buffer address in the array
element. This function acquires into the buffer for each element that
is not NULL.
/// </param>
/// <param name="SkipCount">array containing the number of images to
skip before each acquisition.
/// Note: skipCount is not supported for line scan acquisitions.
/// Refer to imgSessionLineTrigSource2 for information about
triggering line scan skip triggers.
/// Note: skipCount is not supported on the NI 1427, NI 1429, or NI
1430.
/// </param>
/// <param name="StartNow">non-zero value specifies that the continuous
acquisition should start immediately.
/// If the value is zero, you must manually start the acquisition with
imgSessionStartAcquisition.
/// </param>
/// <param name="Async">if async is zero and startNow is non-zero, this
function does not return until the acquisition completes.
/// Otherwise, the function returns immediately.
/// </param>
/// <returns>This function returns 0 on success. On failure, this
function returns an error code.
/// For information about the error code, call imgShowError.
/// </returns>

Anyone have any ideas? I dont have much experience with interop