String Compression

Download Chilkat Crypt ActiveX

Visual Basic example to compress and decompress a string. This example demonstrates string-to-string compression. It is only worth doing if the input string is long enough and compresses well enough. The output of any compression algorithm is binary. To convert binary data to a printable string, some sort of encoding must be applied -- and this alway expands the size. For example, hex encoding produces a string that is 2 character for each byte (i.e. it doubles the size). Base64 encoding is a better choice because the output is 4 characters for every 3 bytes encoded.

'  The Crypt component has the BZip2 compression
'  and decompression features, combined with encoding/decoding,
'  that is required for string-to-string compression.
Dim crypt As New ChilkatCrypt2

'  Any string argument automatically begins the 30-day trial.
Dim success As Long
success = crypt.UnlockComponent("30-day trial")
If (success <> 1) Then
    MsgBox "Crypt component unlock failed"
    Exit Sub
End If

Dim s As String
s = "A friend called me up the other day and talked about investing in a dot-com"
s = s & " that sells lobsters. Internet lobsters. Where will this end? --Donald Trump"

'  Make this string a bit bigger...
s = s + s
s = s + s
s = s + s

crypt.CryptAlgorithm = "none"
crypt.EncodingMode = "base64"

Dim compressed As String
compressed = crypt.CompressStringENC(s)

Text1.Text = Text1.Text & compressed & vbCrLf
Text1.Refresh

Dim decompressed As String
decompressed = crypt.InflateStringENC(compressed)

Text1.Text = Text1.Text & decompressed & vbCrLf
Text1.Refresh