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  1. #1
    Join Date
    Oct 2012

    AccessViolationException on API Call

    I migrated a VB6 ActiveX to Vb.Net and I am having an issue on API Calls.
    The ActiveX consist of making API calls to read or write data from flat files.
    It works pretty well in VB6, but throws an exception in Vb.Net : AccessViolationException
    Let me know if you want me to post the working VB6 Code

    Also, I apologize for my english skills. =)

    Here is the VB.Net Code:

    Module nif_types
    'Define structure for RGETDAT_BITS procedure call
        <StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)> _
        Public Structure rgetdat_bits_data_str
            Dim type As Short 'data type (set internally)
            Dim file As Short 'file in database
            Dim rec As Short 'record in file
            Dim word As Short 'word offset in record
            Dim start_bit As Short 'start bit in word
            Dim length As Short 'number of bits
            Dim flags As Short 'flags
            Dim padding As Short
            Dim value As Short 'database value
            <VBFixedArray(2)> Dim padV() As Short
            Dim status As Short 'return status
            <VBFixedArray(2)> Dim padA() As Short
            Public Sub Initialize()
                ReDim padV(2)
                ReDim padA(2)
            End Sub
        End Structure
    End Module
    Module HSCNAPI
    Public Declare Function rgetdat_bits Lib "hscnetapi.dll" Alias "rgetdat_bits_vb" (ByVal Server As String, ByVal num_points As Short, ByRef getdat_bits_data() As rgetdat_bits_data_str) As Short
    End Module
    Class MyControl
    <MarshalAs(UnmanagedType.ByValTStr, SizeConst:=255)> Dim ServerName As String ' For fixed length compatibility
     Public Sub GetServerName()
                    ServerName = RegQuery("Honeywell", "Experion PKS Server", "Server", "ConnectedServerName")
     End Sub
     Public Function HSC_get_bits_data(ByVal iFile As Short, ByVal iRec As Short, ByVal iWord As Short, ByVal iStart As Short, Optional ByVal DataNumber As Integer = 1) As Array
                Dim ArrData(0) As rgetdat_bits_data_str
                Dim ArrReturn(0 To 100) As String
                Dim iWordCount As Integer = 0
                Dim iBitCount As Integer = 0
                    For i As Integer = 0 To DataNumber - 1
                        ArrData(0).file = (iFile)
                        ArrData(0).rec = Convert.ToInt16(iRec)
                        ArrData(0).word = Convert.ToInt16(iWord + iWordCount)
                        ArrData(0).start_bit = Convert.ToInt16(iStart + iBitCount)
                        ArrData(0).length = Convert.ToInt16(1)
                        ArrData(0).flags = Convert.ToInt16(0)
                        rgetdat_bits(ServerName, Convert.ToInt16(1), ArrData) ' <------------------- Stacktrace shows this Exception happens on this line, which is the API Call
                        ArrReturn(i) = CStr(ArrData(0).value)
                        iBitCount += 1 ' Counter to increment the StartBit by 1: 1 bit = 1 bit. 
                        If iBitCount = 16 Then ' 0 to 15 represent 16 bits. When 16 bit count is reached, increment word and reset bit counter
                            iWordCount += 1
                            iBitCount = 0
                        End If
                    Return ArrReturn
                Catch Ex1 As AccessViolationException
                    'mylogWriter.WriteLine("Record Time: " & time.ToString(timeformat) & " :: " & "HSC_get_bits_data: " & Ex1.Message, Ex1.InnerException.ToString)
                Catch Ex As Exception
                    'mylogWriter.WriteLine("Record Time: " & time.ToString(timeformat) & " :: " & "HSC_get_bits_data: " & Ex.Message, Ex.InnerException.ToString)
                End Try
                Return Nothing
            End Function
    End Class

  2. #2
    Join Date
    Jun 2005
    JHB South Africa

    Re: AccessViolationException on API Call

    I think we'll need to see the working Structure in the VB6 side of things...

    Sure it's a probably a bad structure problem...
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