return and reuse HANDLE from unmanaged c++ code

[dwuser22]

Using VB .NET 4.0 , I'm trying to run through some c++ unmanaged code..

The issue is that one function returns a HANDLE, and another needs the same HANDLE ref. I can tell the initial function is running successfully, but afterwards, the IntPtr is set to 0 (blank).

Naturally, it's driving me crazy, since this is the first time I've really had to work with P/Invoke. Unfortunately, I'm not sure what the HANDLE points too, since it's being returned from a file in an old compiled lib

Can * anyone * help with this? I've included the code below.


The unmanaged C++ code:

int log_connect(char* node, UINT dte, HANDLE* ptr_log)
{
   HANDLE    hLog = NULL;
   int       rc = 0;

   rc = EmEvt_logOpen( node, dte, EMEVT_LOG_MODE_READ, &hLog );


   ptr_log = &hLog;

   return rc;
}

int log_read(HANDLE* ptr_log, EMEVT_LOG* ptr_evt)
{

	int rc = 0;
	rc = EmEvt_logRead( *ptr_log, 0, *ptr_evt );

	return rc;
   
}

My managed vb .net code (console app):

 <DllImport("em_utilities.dll", CharSet:=CharSet.Auto)> _
    Public Function log_connect(<MarshalAs(UnmanagedType.LPStr)> ByVal node As String, <MarshalAs(UnmanagedType.U4)> ByVal dte As UInteger, ByRef ptr_log As IntPtr) As Integer
    End Function

<DllImport("em_utilities.dll", CharSet:=CharSet.Auto)> _
Private Shared Function log_read(ByRef ptr_log As IntPtr) As Integer
        End Function

'Get today's date in requested format
Dim dte As UInteger = 10000 * DateTime.Today.Year + 100 * DateTime.Today.Month.ToString() + DateTime.Today.Day

Dim log As IntPtr

log_connect("server", dte, log)

If log = IntPtr.Zero Then
    System.Console.WriteLine("IntPtr blank")
End If

log_read(log)

[HanneSThEGreaT]

Some issues with your code :

int log_connect(char* node, UINT dte, HANDLE* ptr_log){

int, may be equivalent to the short data type, so use short ineatd of Integer in VB

Dim log As IntPtr '-- > Here you are declaring the IntPtr

log_connect("server", dte, log) '-->Here you are using it, it still being ZERO

If log = IntPtr.Zero Then '--> It is obviously still Zero