cGZip.cls

A standalone, pure VB6 Class for GZIP Compression and Decompression.

This class provides a simple and effective way to handle GZIP-formatted data directly in memory or for file-to-file operations, without requiring any external DLLs like zlibwapi.dll.

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Acknowledgements

This class is a heavily simplified adaptation of the brilliant and far more comprehensive cZipArchive.cls by wqweto.

The core DEFLATE algorithm, machine code thunk, and the ingenious method of executing it from VB6 were originally engineered by him. This cGZip.cls was created by isolating the DEFLATE/GZIP logic from his larger ZIP archive project.

Full credit for the core engine belongs to him. You can find the original, full-featured project here:

• Original Repository: https://github.com/wqweto/ZipArchive

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Usage

1. Getting Started

Just, add the cGZip.cls file to your Visual Basic 6 project.

2. Definition & Basic Example

To use the class, create a new instance of it. All compression and decompression functions are available as methods of this object.

' Create an instance of the class
Dim GZip As New cGZip

' Define source and destination files
Dim sourceFile As String
sourceFile = App.Path & "\MyDocument.txt"
Dim compressedFile As String
compressedFile = App.Path & "\MyDocument.txt.gz"

' Create a dummy source file for the example
Dim hFile As Integer
hFile = FreeFile
Open sourceFile For Output As #hFile
Print #hFile, "This is a test of the cGZip class using custom enum flags."
Close #hFile

' Compress the file using the ULTRA compression level from your enum
Dim bOK As Boolean
bOK = GZip.CompressFileToGz(sourceFile, compressedFile, GZ_ULTRA_COMPRESSION)

If bOK Then
    MsgBox "File compressed successfully!", vbInformation
Else
    MsgBox "Compression failed: " & GZip.LastError, vbCritical
End If

API Reference

Public Properties

• LastError As String (Read-Only) Returns a description of the last error that occurred.

Compression Level Flags

The class and its helper functions use the GzipCompressionLevel enumeration to set the compression level. This provides readable names for the available settings.

• GZ_NO_COMPRESSION (Value: 0) - Store only, no compression.

• GZ_FASTEST_COMPRESSION (Value: 1) - Fastest speed, minimal compression.

• GZ_NORMAL_COMPRESSION (Value: 5) - A standard compression level.

• GZ_MAX_COMPRESSION (Value: 7) - (Default) A great balance between speed and size. This level is used if no other level is specified.

• GZ_ULTRA_COMPRESSION (Value: 9) - Best possible compression, but the slowest process.

Core Methods (Buffer-to-Buffer)

• Compress(sourceBuffer() As Byte, [Optional Level As GzipCompressionLevel = GZ_DEFAULT_COMPRESSION]) As Byte() Compresses a source byte array into a new GZ-formatted byte array.

• Decompress(gzBuffer() As Byte) As Byte() Decompresses a GZ-formatted byte array into the original byte array.

Helper Methods (File Operations)

• CompressFileToGz(sourceFilePath As String, destGzPath As String, [Optional Level As GzipCompressionLevel = GZ_DEFAULT_COMPRESSION]) As Boolean Compresses a source file on disk to a new .gz file on disk. Returns True on success.

• DecompressGzToFile(sourceGzPath As String, destFilePath As String) As Boolean Decompresses a .gz file from disk to a new, uncompressed file on disk. Returns True on success.

• CompressFileToBuffer(sourceFilePath As String, [Optional Level As GzipCompressionLevel = GZ_DEFAULT_COMPRESSION]) As Byte() Reads a file from disk and returns its GZ-compressed content as a byte array.

• DecompressBufferToFile(gzBuffer() As Byte, destFilePath As String) As Boolean Decompresses a GZ-formatted byte array and writes the result to a file on disk. Returns True on success.