Visual Basic 6.0

Compressing StringBuilder Data Using CompressSb (Single Call and Chunked)

See more Compression Examples

This example demonstrates how to compress text stored in a StringBuilder using the CompressSb method in two ways:

1. Single-call compression, where the entire input is compressed in one operation.
2. Chunked compression, where the input is split into multiple parts and processed sequentially using the FirstChunk and LastChunk properties.

The example shows how compressed output is appended to a BinData object, and how the result can be verified by decompressing back to the original text. This is useful for both simple use cases and scenarios where data is processed incrementally (such as streaming or large inputs).

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Key Points

• CompressSb converts text to bytes using the Charset property (UTF-8 recommended).
• Compressed data is appended to a BinData object.
• When both FirstChunk and LastChunk are true, compression is done in a single call.
• For chunked processing:
  • First chunk → FirstChunk = true, LastChunk = false
  • Middle chunks → both false
  • Final chunk → LastChunk = true
• Chunked compression is useful when processing data incrementally.

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.

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

' ================================================================
' 1) Single-call compression (entire data in one call)
' ================================================================

Dim sb As New ChilkatStringBuilder
success = sb.Append("The quick brown fox jumps over the lazy dog. ")
success = sb.Append("This is a simple example using CompressSb.")

Dim bdCompressed As New ChilkatBinData

' When both FirstChunk and LastChunk are true (the defaults),
' the entire compression happens in a single call.
compress.FirstChunk = 1
compress.LastChunk = 1

success = compress.CompressSb(sb,bdCompressed)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

Dim compressedBase64 As String
compressedBase64 = bdCompressed.GetEncoded("base64")

Debug.Print "Single-call compressed (base64):"
Debug.Print compressedBase64

' ================================================================
' 2) Chunked compression using FirstChunk / LastChunk
' ================================================================

Dim bdChunkedOut As New ChilkatBinData

' First chunk
compress.FirstChunk = 1
compress.LastChunk = 0

Dim sbPart As New ChilkatStringBuilder
success = sbPart.Append("The quick brown fox ")

success = compress.CompressSb(sbPart,bdChunkedOut)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

' Middle chunk
compress.FirstChunk = 0
compress.LastChunk = 0

sbPart.Clear 
success = sbPart.Append("jumps over the lazy dog. ")

success = compress.CompressSb(sbPart,bdChunkedOut)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

' Final chunk
compress.FirstChunk = 0
compress.LastChunk = 1

sbPart.Clear 
success = sbPart.Append("This is a chunked CompressSb example.")

success = compress.CompressSb(sbPart,bdChunkedOut)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

Dim chunkedBase64 As String
chunkedBase64 = bdChunkedOut.GetEncoded("base64")

Debug.Print "Chunked compressed (base64):"
Debug.Print chunkedBase64

' ================================================================
' 3) Decompress to verify correctness
' ================================================================

Dim sbDecompressed As New ChilkatStringBuilder

' Decompress in a single call (entire data already assembled)
compress.FirstChunk = 1
compress.LastChunk = 1

success = compress.DecompressSb(bdChunkedOut,sbDecompressed)
If (success = 0) Then
    Debug.Print compress.LastErrorText
    Exit Sub
End If

Debug.Print "Decompressed text:"
Debug.Print sbDecompressed.GetAsString()