See below some functions declarations for Visual Basic.

Frequently Asked Question:

Q: Each time I use the compress function I get the -5 error (not enough
  room in the output buffer).

A: Make sure that the length of the compressed buffer is passed by
  reference ("as any"), not by value ("as long"). Also check that
  before the call of compress this length is equal to the total size of
  the compressed buffer and not zero.


From: "Jon Caruana" <[email protected]>
Subject: Re: How to port zlib declares to vb?
Date: Mon, 28 Oct 1996 18:33:03 -0600

Got the answer! (I haven't had time to check this but it's what I got, and
looks correct):

He has the following routines working:
       compress
       uncompress
       gzopen
       gzwrite
       gzread
       gzclose

Declares follow: (Quoted from Carlos Rios <[email protected]>, in Vb4 form)

#If Win16 Then   'Use Win16 calls.
Declare Function compress Lib "ZLIB.DLL" (ByVal compr As
       String, comprLen As Any, ByVal buf As String, ByVal buflen
       As Long) As Integer
Declare Function uncompress Lib "ZLIB.DLL" (ByVal uncompr
       As String, uncomprLen As Any, ByVal compr As String, ByVal
       lcompr As Long) As Integer
Declare Function gzopen Lib "ZLIB.DLL" (ByVal filePath As
       String, ByVal mode As String) As Long
Declare Function gzread Lib "ZLIB.DLL" (ByVal file As
       Long, ByVal uncompr As String, ByVal uncomprLen As Integer)
       As Integer
Declare Function gzwrite Lib "ZLIB.DLL" (ByVal file As
       Long, ByVal uncompr As String, ByVal uncomprLen As Integer)
       As Integer
Declare Function gzclose Lib "ZLIB.DLL" (ByVal file As
       Long) As Integer
#Else
Declare Function compress Lib "ZLIB32.DLL"
       (ByVal compr As String, comprLen As Any, ByVal buf As
       String, ByVal buflen As Long) As Integer
Declare Function uncompress Lib "ZLIB32.DLL"
       (ByVal uncompr As String, uncomprLen As Any, ByVal compr As
       String, ByVal lcompr As Long) As Long
Declare Function gzopen Lib "ZLIB32.DLL"
       (ByVal file As String, ByVal mode As String) As Long
Declare Function gzread Lib "ZLIB32.DLL"
       (ByVal file As Long, ByVal uncompr As String, ByVal
       uncomprLen As Long) As Long
Declare Function gzwrite Lib "ZLIB32.DLL"
       (ByVal file As Long, ByVal uncompr As String, ByVal
       uncomprLen As Long) As Long
Declare Function gzclose Lib "ZLIB32.DLL"
       (ByVal file As Long) As Long
#End If

-Jon Caruana
[email protected]
Microsoft Sitebuilder Network Level 1 Member - HTML Writer's Guild Member


Here is another example from Michael <[email protected]> that he
says conforms to the VB guidelines, and that solves the problem of not
knowing the uncompressed size by storing it at the end of the file:

'Calling the functions:
'bracket meaning: <parameter> [optional] {Range of possible values}
'Call subCompressFile(<path with filename to compress> [, <path with
filename to write to>, [level of compression {1..9}]])
'Call subUncompressFile(<path with filename to compress>)

Option Explicit
Private lngpvtPcnSml As Long 'Stores value for 'lngPercentSmaller'
Private Const SUCCESS As Long = 0
Private Const strFilExt As String = ".cpr"
Private Declare Function lngfncCpr Lib "zlib.dll" Alias "compress2" (ByRef
dest As Any, ByRef destLen As Any, ByRef src As Any, ByVal srcLen As Long,
ByVal level As Integer) As Long
Private Declare Function lngfncUcp Lib "zlib.dll" Alias "uncompress" (ByRef
dest As Any, ByRef destLen As Any, ByRef src As Any, ByVal srcLen As Long)
As Long

Public Sub subCompressFile(ByVal strargOriFilPth As String, Optional ByVal
strargCprFilPth As String, Optional ByVal intLvl As Integer = 9)
   Dim strCprPth As String
   Dim lngOriSiz As Long
   Dim lngCprSiz As Long
   Dim bytaryOri() As Byte
   Dim bytaryCpr() As Byte
   lngOriSiz = FileLen(strargOriFilPth)
   ReDim bytaryOri(lngOriSiz - 1)
   Open strargOriFilPth For Binary Access Read As #1
       Get #1, , bytaryOri()
   Close #1
   strCprPth = IIf(strargCprFilPth = "", strargOriFilPth, strargCprFilPth)
'Select file path and name
   strCprPth = strCprPth & IIf(Right(strCprPth, Len(strFilExt)) =
strFilExt, "", strFilExt) 'Add file extension if not exists
   lngCprSiz = (lngOriSiz * 1.01) + 12 'Compression needs temporary a bit
more space then original file size
   ReDim bytaryCpr(lngCprSiz - 1)
   If lngfncCpr(bytaryCpr(0), lngCprSiz, bytaryOri(0), lngOriSiz, intLvl) =
SUCCESS Then
       lngpvtPcnSml = (1# - (lngCprSiz / lngOriSiz)) * 100
       ReDim Preserve bytaryCpr(lngCprSiz - 1)
       Open strCprPth For Binary Access Write As #1
           Put #1, , bytaryCpr()
           Put #1, , lngOriSiz 'Add the the original size value to the end
(last 4 bytes)
       Close #1
   Else
       MsgBox "Compression error"
   End If
   Erase bytaryCpr
   Erase bytaryOri
End Sub

Public Sub subUncompressFile(ByVal strargFilPth As String)
   Dim bytaryCpr() As Byte
   Dim bytaryOri() As Byte
   Dim lngOriSiz As Long
   Dim lngCprSiz As Long
   Dim strOriPth As String
   lngCprSiz = FileLen(strargFilPth)
   ReDim bytaryCpr(lngCprSiz - 1)
   Open strargFilPth For Binary Access Read As #1
       Get #1, , bytaryCpr()
   Close #1
   'Read the original file size value:
   lngOriSiz = bytaryCpr(lngCprSiz - 1) * (2 ^ 24) _
             + bytaryCpr(lngCprSiz - 2) * (2 ^ 16) _
             + bytaryCpr(lngCprSiz - 3) * (2 ^ 8) _
             + bytaryCpr(lngCprSiz - 4)
   ReDim Preserve bytaryCpr(lngCprSiz - 5) 'Cut of the original size value
   ReDim bytaryOri(lngOriSiz - 1)
   If lngfncUcp(bytaryOri(0), lngOriSiz, bytaryCpr(0), lngCprSiz) = SUCCESS
Then
       strOriPth = Left(strargFilPth, Len(strargFilPth) - Len(strFilExt))
       Open strOriPth For Binary Access Write As #1
           Put #1, , bytaryOri()
       Close #1
   Else
       MsgBox "Uncompression error"
   End If
   Erase bytaryCpr
   Erase bytaryOri
End Sub
Public Property Get lngPercentSmaller() As Long
   lngPercentSmaller = lngpvtPcnSml
End Property

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