Visual Basic 6.0

Compress and Decompress Base64

See more Compression Examples

This example demonstrates how to compress and decompress binary data using the Chilkat.Compression class with the BinData object.

The input data is provided as a Base64-encoded string. It is first decoded into raw bytes and loaded into a BinData object. The example then compresses the data in-place using the deflate algorithm. Because compressed data is binary, it is re-encoded to Base64 for easy display and transport.

To verify correctness, the example performs the reverse operation: it decodes the compressed Base64 back to bytes, decompresses the data, and encodes the result to Base64 again. The final Base64 output is compared with the original input to confirm that the compression and decompression process preserved the data exactly.

This example highlights:

• Using BinData to hold and transform binary data
• In-place compression and decompression with CompressBd and DecompressBd
• Converting between binary data and Base64 for display or transmission
• Verifying round-trip integrity after compression and decompression

Visual Basic 6.0

Dim success As Long
success = 0

' This example assumes the Chilkat API has already been unlocked.
' See Global Unlock Sample for sample code.

' This is the original data, encoded as base64.
' It decodes to plain text containing several repeated lines.
Dim originalBase64 As String
originalBase64 = "VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wZWQgb3ZlciB0aGUgbGF6eSBkb2cuDQpUaGUgcXVpY2sgYnJvd24gZm94IGp1bXBlZCBvdmVyIHRoZSBsYXp5IGRvZy4NClRoZSBxdWljayBicm93biBmb3gganVtcGVkIG92ZXIgdGhlIGxhenkgZG9nLg0KVGhlIHF1aWNrIGJyb3duIGZveCBqdW1wZWQgb3ZlciB0aGUgbGF6eSBkb2cuDQpUaGUgcXVpY2sgYnJvd24gZm94IGp1bXBlZCBvdmVyIHRoZSBsYXp5IGRvZy4NCg0K"

Dim compress As New ChilkatCompression
compress.Algorithm = "deflate"

' Load the original base64 data into a BinData object.
' AppendEncoded decodes the base64 and stores the decoded bytes in binData.
Dim binData As New ChilkatBinData
success = binData.AppendEncoded(originalBase64,"base64")
If (success = 0) Then
    Debug.Print "Failed to decode the original base64 data."
    Exit Sub
End If

' Compress the bytes contained in binData.
' CompressBd modifies binData in-place, replacing the original bytes
' with the compressed bytes.
success = compress.CompressBd(binData)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

' Show the compressed result as base64 so it can be printed as text.
Dim compressedBase64 As String
compressedBase64 = binData.GetEncoded("base64")

Debug.Print "Compressed data, base64 encoded:"
Debug.Print compressedBase64

' Expected compressed base64:
' C8lIVSgszUzOVkgqyi/PU0jLr1DIKs0tSE1RyC9LLVIoAcrnJFZVKqTkp+vxcoUMYeW8XAA=

' --------------------------------------------------------------------
' Decompress the data to verify that we get back the original bytes.
' --------------------------------------------------------------------

' Start with a fresh BinData object containing the compressed bytes.
' The compressed data is currently represented as base64 text, so decode it
' back to bytes before calling DecompressBd.
success = binData.Clear()
success = binData.AppendEncoded(compressedBase64,"base64")
If (success = 0) Then
    Debug.Print "Failed to decode the compressed base64 data."
    Exit Sub
End If

' DecompressBd also modifies binData in-place, replacing the compressed bytes
' with the decompressed bytes.
success = compress.DecompressBd(binData)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

' Encode the decompressed bytes as base64 so we can compare them with the
' original base64 input.
Dim decompressedBase64 As String
decompressedBase64 = binData.GetEncoded("base64")

Debug.Print "Decompressed data, base64 encoded:"
Debug.Print decompressedBase64

' The decompressed base64 should match the original base64 input.
If (decompressedBase64 = originalBase64) Then
    Debug.Print "Success. The decompressed data matches the original data."
Else
    Debug.Print "Failure. The decompressed data does not match the original data."
End If