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Compressing and Decompressing Files Using Streaming (CompressFile / DecompressFile)

See more Compression Examples

This example demonstrates how to compress a file to a binary format and then restore it using the Chilkat.Compression class. The CompressFile method reads the source file, compresses it using the specified algorithm, and writes the result to a destination file. The DecompressFile method performs the reverse operation, restoring the original file from the compressed data.

Both operations are performed internally in streaming mode, allowing files of any size to be processed efficiently without loading the entire file into memory. The example also includes a simple verification step by comparing file sizes to confirm that the decompressed output matches the original input.

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Dim success As Boolean
success = False

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

Dim compress As New Chilkat.Compression

// Use the zlib algorithm (recommended for general use)
compress.Algorithm = "zlib"

// ------------------------------------------------------------------
// Compress a file
// ------------------------------------------------------------------

Dim inputFile As String
inputFile = "c:/temp/example.txt"
Dim compressedFile As String
compressedFile = "c:/temp/example.txt.zlib"

success = compress.CompressFile(inputFile,compressedFile)
If (success = False) Then
    System.DebugLog("Compression failed:")
    System.DebugLog(compress.LastErrorText)
    Return
End If

System.DebugLog("File compressed successfully:")
System.DebugLog("  Input:      " + inputFile)
System.DebugLog("  Compressed: " + compressedFile)

// ------------------------------------------------------------------
// Decompress the file back to its original form
// ------------------------------------------------------------------

Dim decompressedFile As String
decompressedFile = "c:/temp/example_restored.txt"

success = compress.DecompressFile(compressedFile,decompressedFile)
If (success = False) Then
    System.DebugLog("Decompression failed:")
    System.DebugLog(compress.LastErrorText)
    Return
End If

System.DebugLog("File decompressed successfully:")
System.DebugLog("  Output: " + decompressedFile)

// ------------------------------------------------------------------
// Optional: Verify file sizes (basic sanity check)
// ------------------------------------------------------------------

Dim fac As New Chilkat.FileAccess

Dim originalSize As Int32
originalSize = fac.FileSize(inputFile)
Dim restoredSize As Int32
restoredSize = fac.FileSize(decompressedFile)

System.DebugLog("Original file size:   " + Str(originalSize))
System.DebugLog("Restored file size:   " + Str(restoredSize))

If (originalSize = restoredSize) Then
    System.DebugLog("Sizes match (basic verification successful).")
Else
    System.DebugLog("Warning: File sizes differ.")
End If