1See below some functions declarations for Visual Basic.
2
3Frequently Asked Question:
4
5Q: Each time I use the compress function I get the -5 error (not enough
6   room in the output buffer).
7
8A: Make sure that the length of the compressed buffer is passed by
9   reference ("as any"), not by value ("as long"). Also check that
10   before the call of compress this length is equal to the total size of
11   the compressed buffer and not zero.
12
13
14From: "Jon Caruana" <jon-net@usa.net>
15Subject: Re: How to port zlib declares to vb?
16Date: Mon, 28 Oct 1996 18:33:03 -0600
17
18Got the answer! (I haven't had time to check this but it's what I got, and
19looks correct):
20
21He has the following routines working:
22        compress
23        uncompress
24        gzopen
25        gzwrite
26        gzread
27        gzclose
28
29Declares follow: (Quoted from Carlos Rios <c_rios@sonda.cl>, in Vb4 form)
30
31#If Win16 Then   'Use Win16 calls.
32Declare Function compress Lib "ZLIB.DLL" (ByVal compr As
33        String, comprLen As Any, ByVal buf As String, ByVal buflen
34        As Long) As Integer
35Declare Function uncompress Lib "ZLIB.DLL" (ByVal uncompr
36        As String, uncomprLen As Any, ByVal compr As String, ByVal
37        lcompr As Long) As Integer
38Declare Function gzopen Lib "ZLIB.DLL" (ByVal filePath As
39        String, ByVal mode As String) As Long
40Declare Function gzread Lib "ZLIB.DLL" (ByVal file As
41        Long, ByVal uncompr As String, ByVal uncomprLen As Integer)
42        As Integer
43Declare Function gzwrite Lib "ZLIB.DLL" (ByVal file As
44        Long, ByVal uncompr As String, ByVal uncomprLen As Integer)
45        As Integer
46Declare Function gzclose Lib "ZLIB.DLL" (ByVal file As
47        Long) As Integer
48#Else
49Declare Function compress Lib "ZLIB32.DLL"
50        (ByVal compr As String, comprLen As Any, ByVal buf As
51        String, ByVal buflen As Long) As Integer
52Declare Function uncompress Lib "ZLIB32.DLL"
53        (ByVal uncompr As String, uncomprLen As Any, ByVal compr As
54        String, ByVal lcompr As Long) As Long
55Declare Function gzopen Lib "ZLIB32.DLL"
56        (ByVal file As String, ByVal mode As String) As Long
57Declare Function gzread Lib "ZLIB32.DLL"
58        (ByVal file As Long, ByVal uncompr As String, ByVal
59        uncomprLen As Long) As Long
60Declare Function gzwrite Lib "ZLIB32.DLL"
61        (ByVal file As Long, ByVal uncompr As String, ByVal
62        uncomprLen As Long) As Long
63Declare Function gzclose Lib "ZLIB32.DLL"
64        (ByVal file As Long) As Long
65#End If
66
67-Jon Caruana
68jon-net@usa.net
69Microsoft Sitebuilder Network Level 1 Member - HTML Writer's Guild Member
70
71
72Here is another example from Michael <michael_borgsys@hotmail.com> that he
73says conforms to the VB guidelines, and that solves the problem of not
74knowing the uncompressed size by storing it at the end of the file:
75
76'Calling the functions:
77'bracket meaning: <parameter> [optional] {Range of possible values}
78'Call subCompressFile(<path with filename to compress> [, <path with
79filename to write to>, [level of compression {1..9}]])
80'Call subUncompressFile(<path with filename to compress>)
81
82Option Explicit
83Private lngpvtPcnSml As Long 'Stores value for 'lngPercentSmaller'
84Private Const SUCCESS As Long = 0
85Private Const strFilExt As String = ".cpr"
86Private Declare Function lngfncCpr Lib "zlib.dll" Alias "compress2" (ByRef
87dest As Any, ByRef destLen As Any, ByRef src As Any, ByVal srcLen As Long,
88ByVal level As Integer) As Long
89Private Declare Function lngfncUcp Lib "zlib.dll" Alias "uncompress" (ByRef
90dest As Any, ByRef destLen As Any, ByRef src As Any, ByVal srcLen As Long)
91As Long
92
93Public Sub subCompressFile(ByVal strargOriFilPth As String, Optional ByVal
94strargCprFilPth As String, Optional ByVal intLvl As Integer = 9)
95    Dim strCprPth As String
96    Dim lngOriSiz As Long
97    Dim lngCprSiz As Long
98    Dim bytaryOri() As Byte
99    Dim bytaryCpr() As Byte
100    lngOriSiz = FileLen(strargOriFilPth)
101    ReDim bytaryOri(lngOriSiz - 1)
102    Open strargOriFilPth For Binary Access Read As #1
103        Get #1, , bytaryOri()
104    Close #1
105    strCprPth = IIf(strargCprFilPth = "", strargOriFilPth, strargCprFilPth)
106'Select file path and name
107    strCprPth = strCprPth & IIf(Right(strCprPth, Len(strFilExt)) =
108strFilExt, "", strFilExt) 'Add file extension if not exists
109    lngCprSiz = (lngOriSiz * 1.01) + 12 'Compression needs temporary a bit
110more space then original file size
111    ReDim bytaryCpr(lngCprSiz - 1)
112    If lngfncCpr(bytaryCpr(0), lngCprSiz, bytaryOri(0), lngOriSiz, intLvl) =
113SUCCESS Then
114        lngpvtPcnSml = (1# - (lngCprSiz / lngOriSiz)) * 100
115        ReDim Preserve bytaryCpr(lngCprSiz - 1)
116        Open strCprPth For Binary Access Write As #1
117            Put #1, , bytaryCpr()
118            Put #1, , lngOriSiz 'Add the the original size value to the end
119(last 4 bytes)
120        Close #1
121    Else
122        MsgBox "Compression error"
123    End If
124    Erase bytaryCpr
125    Erase bytaryOri
126End Sub
127
128Public Sub subUncompressFile(ByVal strargFilPth As String)
129    Dim bytaryCpr() As Byte
130    Dim bytaryOri() As Byte
131    Dim lngOriSiz As Long
132    Dim lngCprSiz As Long
133    Dim strOriPth As String
134    lngCprSiz = FileLen(strargFilPth)
135    ReDim bytaryCpr(lngCprSiz - 1)
136    Open strargFilPth For Binary Access Read As #1
137        Get #1, , bytaryCpr()
138    Close #1
139    'Read the original file size value:
140    lngOriSiz = bytaryCpr(lngCprSiz - 1) * (2 ^ 24) _
141              + bytaryCpr(lngCprSiz - 2) * (2 ^ 16) _
142              + bytaryCpr(lngCprSiz - 3) * (2 ^ 8) _
143              + bytaryCpr(lngCprSiz - 4)
144    ReDim Preserve bytaryCpr(lngCprSiz - 5) 'Cut of the original size value
145    ReDim bytaryOri(lngOriSiz - 1)
146    If lngfncUcp(bytaryOri(0), lngOriSiz, bytaryCpr(0), lngCprSiz) = SUCCESS
147Then
148        strOriPth = Left(strargFilPth, Len(strargFilPth) - Len(strFilExt))
149        Open strOriPth For Binary Access Write As #1
150            Put #1, , bytaryOri()
151        Close #1
152    Else
153        MsgBox "Uncompression error"
154    End If
155    Erase bytaryCpr
156    Erase bytaryOri
157End Sub
158Public Property Get lngPercentSmaller() As Long
159    lngPercentSmaller = lngpvtPcnSml
160End Property
161