Marshalling and callback with Unmanaged dll

[arunraj_v1]

Hi,
I have the following structures in a C dll,


In C:

typedef struct Structure1
{
SomeStruct list1;// Somestruct is a structure
SomeStruct List2;
SomeEnum state; // SomeEnum is a Enum
unsigned char *pcurrent;
unsigned short Length;
SomeStruct addr;
SomeStruct timer;
unsigned short retries;
unsigned char flag;
unsigned short seq;
someEnum2 Mtype;
unsigned char action;
unsigned int size;
unsigned char *ptr; //data segment
}struct1;

typedef struct Structure2
{
struct1 Msg;
}struct2;




for the above structures, i have written the following structures in C#,


In C#:

[StructLayout(LayoutKind.Sequential)]
public struct struct1
{
public int List1;
public int List2;
public someenum State;
public int pCurrent;
public short Len;
public int Addr;
public int Timer;
public ushort Retries;
public char Flags;
public ushort SeqNum;
public ushort InvokeId;
public someenum MType;
public char Action;
public int DataBuffSize;
[MarshalAs(UnmanagedType.ByValArray, SizeConst = 10000)]
public byte[] ptr;
}

[StructLayout(LayoutKind.Sequential)]
public struct struct2
{
public struct1 Msg;
}



and i have the following callback function in the managedcode.



In C#:

public void CallBack(long hDev, ref struct2 pData);



This callback function is invoked by a function in unmanaged code.
I have written the following delegate for the callback function,



[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
public delegate void CallBack_delegate(long hDev, ref struct2 pData);

public static CallBack_delegate call_del = CallBack;


I am getting Access violation exception when the call back funciton is executed.

pls help.