For all the newcomers to VB.Net (I know this is simple stuff to experienced users), below is a class in VB that compresses and decompresses byte arrrays. Thanks to all the help from other users.
'DATACOMPRESS CLASS - VB.Net
'************************************************* ************************************************** *******
' METHODS:
' CompressBytes(Source ByteArray, Optional Temporay Byte Array
' Compresses ByteArray into Temporary Byte Array or into ByteArray if Temporary Byte Array not input
'
' DeCompressBytes (Source ByteArray, Original Array Size before compression as integer, Optional Temporary Byte Array)
' Decompresses ByteArray into Temporary Byte Array or into ByteArray if Temporary Byte Array not input
'
'************************************************* ************************************************** ********
Imports System.Runtime.InteropServices
Public Class DataCompress
'Declare zlib functions "Compress" and "Uncompress" for compressing Byte Arrays
<DllImport("zlib.DLL", EntryPoint:="compress")> _
Private Shared Function CompressByteArray(ByVal dest As Byte(), ByRef destLen As Integer, ByVal src As Byte(), ByVal srcLen As Integer) As Integer
' Leave function empty - DLLImport attribute forwards calls to CompressByteArray to compress in zlib.dLL
End Function
<DllImport("zlib.DLL", EntryPoint:="uncompress")> _
Private Shared Function UncompressByteArray(ByVal dest As Byte(), ByRef destLen As Integer, ByVal src As Byte(), ByVal srcLen As Integer) As Integer
' Leave function empty - DLLImport attribute forwards calls to UnCompressByteArray to Uncompress in zlib.dLL
End Function
Public Sub New()
MyBase.New()
End Sub
Public Function CompressBytes(ByRef Data() As Byte, Optional ByRef TempBuffer() As Byte = Nothing) As Integer
'Compresses Data into a temp buffer
'Returns compressed Data in Data if TempBuff not specified
'Returns Result = Size of compressed data if ok, -1 if not
Dim OriginalSize As Long = UBound(Data) + 1
'Allocate temporary Byte Array for storage
Dim result As Integer
Dim usenewstorage As Boolean
If TempBuffer Is Nothing Then usenewstorage = False Else usenewstorage = True
Dim BufferSize As Integer = UBound(Data) + 1
BufferSize = CInt(BufferSize + (BufferSize * 0.01) + 12)
ReDim TempBuffer(BufferSize)
'Compress data byte array
result = CompressByteArray(TempBuffer, BufferSize, Data, UBound(Data) + 1)
'Store results
If result = 0 Then
If usenewstorage Then
'Return results in TempBuffer
ReDim Preserve TempBuffer(BufferSize - 1)
Else
'Return compressed Data in original Data Array
' Resize original data array to compressed size
ReDim Data(BufferSize - 1)
' Copy Array to original data array
Array.Copy(TempBuffer, Data, BufferSize)
'Release TempBuffer STorage
TempBuffer = Nothing
End If
Return BufferSize
Else
Return -1
End If
End Function
Public Function DeCompressBytes(ByRef Data() As Byte, ByVal Origsize As Integer, Optional ByRef TempBuffer() As Byte = Nothing) As Integer
'DeCompresses Data into a temp buffer..note that Origsize must be the size of the original data before compression
'Returns compressed Data in Data if TempBuff not specified
'Returns Result = Size of decompressed data if ok, -1 if not
'Allocate memory for buffers
Dim result As Integer
Dim usenewstorage As Boolean
Dim Buffersize As Integer = CInt(Origsize + (Origsize * 0.01) + 12)
If TempBuffer Is Nothing Then usenewstorage = False Else usenewstorage = True
ReDim TempBuffer(Buffersize)
'Decompress data
result = UncompressByteArray(TempBuffer, Origsize, Data, UBound(Data) + 1)
'Truncate buffer to compressed size
If result = 0 Then
If usenewstorage Then
'Return decoompressed data in TempBuffer
ReDim Preserve TempBuffer(Origsize - 1)
Else
'Return decompressed data in original source data file
' Truncate to compressed size
ReDim Data(Origsize - 1)
' Copy Array to original data array
Array.Copy(TempBuffer, Data, Origsize)
'Release TempBuffer STorage
TempBuffer = Nothing
End If
Return Origsize
Else
Return -1
End If
End Function
Protected Overrides Sub Finalize()
MyBase.Finalize()
End Sub
End Class
--
Dennis in Houston
"Dennis" wrote:
Thanks to help from Cor and Herfried, I got it to work as follows:
<DllImport("zlib.DLL", EntryPoint:="compress", SetLastError:=True, CharSet:=CharSet.Unicode, ExactSpelling:=True, _
CallingConvention:=CallingConvention.StdCall)> _
Public Shared Function compressv(ByVal dest As Byte(), ByRef destLen As Integer, ByVal src As Byte(), ByVal srcLen As Integer) As Integer
' Leave function empty - DLLImport attribute forwards calls to compressv to
' compress in zlib.dLL
End Function
After this declaration, you can use normal calling conventions to compressV by specifying byte arrays, integers, etc. Since in VB.Net, a delcare statement for an unmanaged DLL invokes dllimport, I don't understand why M'soft didn't allow standard calling conventions in the Declare statements. But anyway, it works now. Thanks to help I got.
--
Dennis in Houston
"Dennis" wrote:
I am trying to use ZLIB.Dll in a VB.Net project but keep getting an error message that says it can't load the DLL. I tried to add a reference using "Project-Add Reference" but get the error message stating it's not a valid Com component. I'm new to vb.net so any help would be appreciated. Thanks.
--
Dennis in Houston
