Convert c++ to vb.net

Hi,
I covert following code to vb.net

typedef struct {
BYTE sSerialNumber[SERIALNO_LEN];
BYTE byAlarmInPortNum;
BYTE byAlarmOutPortNum;
BYTE byDiskNum;
BYTE byDVRType;
BYTE byChanNum;
BYTE byStartChan;
}NET_DVR_DEVICEINFO, *LPNET_DVR_DEVICEINFO;

LONG NET_DVR_Login(char *sDVRIP,WORD wDVRPort,char *sUserName,char *sPassword,LPNET_DVR_DEVICEINFO lpDeviceInfo);

VB Code:

Public Structure LPNET_DVR_DEVICEINFO
 Public sSerialNumber() As Byte  'serial number
        Public byAlarmInPortNum As Byte 
        Public byAlarmOutPortNum As Byte 
        Public byDiskNum As Byte        
        Public byDVRType As Byte       
        Public byChanNum As Byte     
        Public byStartChan As Byte    
    End Structure
 
  <DllImport("HCNetSDK.dll")> Public Function NET_DVR_Login( _
   ByVal IPAddress() As Char, _
   ByVal DVRPort As UInt16, _
   ByVal UserName() As Char, _
   ByVal Password() As Char, _
   ByRef lpDeviceInfo As LPNET_DVR_DEVICEINFO) As <MarshalAs(I8)> Long
    End Function

When i call this function, always got error "Object reference not set to an instance of an object".
Anyone can help me. Thank you.

Which object are you getting the error on?

Most likely the error occurs when trying to assign a value to the "sSerialNumber()" variable.

When declaring arrays in Structures, you can't assign an initial size to the array. As in:

Code:

---

Public sSerialNumber(4) as Btye

---

Before assigning a value to the "aSerialNumber()" variable, try ReDim-ing it.
As in:

Code:

---

Public LDD As New LPNET_DVR_DEVICEINFO
ReDim LDD.sSerialNumber(4)

NET_DVR_Login(IPAdress, DVRPort, UserName, Password, LDD)

---

I suspect the error may lie in the code where you are calling the function. Could you show it?

Thanks everyone
I find the soultion already.

VB Code:

<StructLayout(LayoutKind.Sequential)> _
   Structure NET_DVR_DEVICEINFO
        <MarshalAs(UnmanagedType.ByValArray, SizeConst:=48)> _
        Dim sSerialNumber() As Byte
        Dim byAlarmInPortNum As Byte
        Dim byAlarmOutPortNum As Byte
        Dim byDiskNum As Byte
        Dim byDVRType As Byte
        Dim byChanNum As Byte
        Dim byStartChan As Byte
    End Structure
 
 
    <DllImport("HCNetSDK.dll", CharSet:=CharSet.Ansi)> _
        Public Shared Function NET_DVR_Login(ByVal sDVRIP As String, _
       ByVal wDVRPort As Short, ByVal sUserName As String _
    , ByVal sPassword As String, ByRef deviceinfo As NET_DVR_DEVICEINFO) As Integer
    End Function