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" <jon-net@usa.net>
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 <c_rios@sonda.cl>, 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
jon-net@usa.net
Microsoft Sitebuilder Network Level 1 Member - HTML Writer's Guild Member


Here is another example from Michael <michael_borgsys@hotmail.com> 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 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