unmanaged code

[avl]

I've to invoke a unmanaged dll fucntion in C# which uses
a callback fucntion.The unmanaged dll fucntion is as
follows

****************************************
The Original Fucntion in the dll
****************************************
int PBORCA_LibraryDirectory ( HPBORCA hORCASession, LPSTR
lpszLibName, LPSTR lpszLibComments, int iCmntsBuffSize,
PBORCA_LISTPROC pListProc, LPVOID pUserData );

hORCASession-Handle to previously established ORCA session

pListProc- Pointer to the PBORCA_LibraryDirectory callback
function.

pUserData -Pointer to user data to be passed to the
PBORCA_LibraryDirectory callback function

Given below function is the callback function declaration
in C.

typedef void (FAR PASCAL *PBORCA_LISTPROC) (
PPBORCA_DIRENTRY, LPVOID );

PPBORCA_DIRENTRY -Pointer to the structure
PBORCA_DIRENTRY, described next
LPVOID -Long pointer to user data

The user data strcuture to the callback fucntion is as
follows:

typedef struct ORCA_UserDataInfo
{
LPSTR lpszBuffer; // Buffer for entry info
DWORD dwCallCount; // # of entries in lib
DWORD dwBufferSize; // size of buffer
DWORD dwBufferOffset; // current offset in buffer
} ORCA_USERDATAINFO, FAR *PORCA_USERDATAINFO;

The structure passed to the callback fucntion by the
LibraryDirectory fucntion is as follows:

typedef struct pborca_direntry { CHAR szComments
[PBORCA_MAXCOMMENT + 1];
LONG lCreateTime;
LONG lEntrySize;
LPSTR lpszEntryName;
PBORCA_TYPE otEntryType;} PBORCA_DIRENTRY, FAR
*PPBORCA_DIRENTRY;

Note:PBORCA_TYPE is an enum
PBORCA_MAXCOMMENT=255
***************************************
End of the dll fucntion
***************************************

_________________________________________
C# code which I've written
_________________________________________

[StructLayout(LayoutKind.Sequential,CharSet=CharSet .Auto)]
public class UserData
{
public string s;
public uint callcount;
public uint bufsize;
public uint offset;
}
[StructLayout(LayoutKind.Sequential,CharSet=CharSet .Auto)]
public struct pborca_direntry
{
public const int i=255;
[MarshalAsUnmanagedType.ByValTStr,SizeConst=i+1)]
public string s;
public System.Int32 time;
public System.Int32 size;
[MarshalAs(UnmanagedType.LPStr)]
public string name;
public int type;
}
public unsafe delegate void Callback(ref pborca_direntry
p,UserData usr);

[DllImport
("pborc80.dll",CharSet=CharSet.Auto,EntryPoint="PB ORCA_Libr
aryDirectory")]
public static extern int LibraryEntry(int hnd,[MarshalAs
(UnmanagedType.LPStr)]System.String s,[Out]char[] buff,int
se,[MarshalAs(UnmanagedType.FunctionPtr)]Callback
hr,UserData usr);


public class1
{
Callback c = new Callback(Class1.libdircallback);
char[] st = new char[10000];
GC.KeepAlive(code=class3.LibraryEntry
(hnd,"d:\\projects\\current\\tgt3.pbl",st,10000,c, usr));

public static void libdircallback(ref pborca_direntry
s,UserData usr)
{
Console.WriteLine("hai,I'm in callback");
Console.WriteLine(s.type);
}

}

Error: The return code is 0 which means the fucntion has
executed successfully. But I'm not getting the correct
values in the structure pborcadirentry.

Note: I've tried GC method. But I'm not sure whether I've
applied it appropriately.I've also tried [MarshalAs
(UnmanagedType.Struct)] and [MarshalAs
(UnmanagedType.LPStruct)] for marshaling structure and
class.But there was no change in the o/p. I feel that
there is some problem in the memory management. But I'm
unable to detect it.

If you need any more information or you have found the
error,please mail me at vi*******@yahoo.com.

Thanks in advance,
Vijaya
..