(Visual FoxPro) Decompress Large Text File in Blocks

Decompresses a large text file in blocks, and compares the restored (decompressed) file with the original to make sure it's correct.

Note: This example requires Chilkat v11.0.0 or greater.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL lnSuccess
LOCAL loCompress
LOCAL loFac
LOCAL lcOriginalPath
LOCAL loFacSrc
LOCAL loFacDest
LOCAL lnBlockSize
LOCAL lnNumBlocks
LOCAL lcRestoredPath
LOCAL lcDecompressedStr
LOCAL loCompressedBytes
LOCAL i
LOCAL lnBEqualContents

lnSuccess = 0

* This example requires the Chilkat API to have been previously unlocked.
* See Global Unlock Sample for sample code.

* First, let's compress a text file.
* We'll then decompress in blocks, and compare the decompressed with the original file.

* Compress a text file:
loCompress = CreateObject('Chilkat.Compression')
loCompress.Algorithm = "deflate"

lnSuccess = loCompress.CompressFile("qa_data/hamlet.xml","qa_data/hamlet_compressed.dat")
IF (lnSuccess = 0) THEN
    ? loCompress.LastErrorText
    RELEASE loCompress
    CANCEL
ENDIF

loFac = CreateObject('Chilkat.FileAccess')

* Examine the uncompressed and compressed sizes:
lcOriginalPath = "qa_data/hamlet.xml"
* Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
* the size of the file as a string, then convert to an integer value.
? "uncompressed size: " + STR(loFac.FileSize(lcOriginalPath))
? "compressed size: " + STR(loFac.FileSize("qa_data/hamlet_compressed.dat"))

* Decompress in blocks..
loFacSrc = CreateObject('Chilkat.FileAccess')
loFacDest = CreateObject('Chilkat.FileAccess')

loFacSrc.OpenForRead("qa_data/hamlet_compressed.dat")

* If we compress in 32K chunks, find out how many blocks there will be.
lnBlockSize = 32768
lnNumBlocks = loFacSrc.GetNumBlocks(lnBlockSize)

* Open an output file for the decompressed data.
lcRestoredPath = "qa_output/hamlet_restored.xml"
lnSuccess = loFacDest.OpenForWrite(lcRestoredPath)
IF (lnSuccess = 0) THEN
    ? loFacDest.LastErrorText
    RELEASE loCompress
    RELEASE loFac
    RELEASE loFacSrc
    RELEASE loFacDest
    CANCEL
ENDIF

* Assuming numBlocks > 1
loCompress.FirstChunk = 1
loCompress.LastChunk = 0

i = 0
DO WHILE i < lnNumBlocks
    loCompressedBytes = loFacSrc.ReadBlock(i,lnBlockSize)
    lcDecompressedStr = loCompress.DecompressString(loCompressedBytes)

    loFacDest.AppendText(lcDecompressedStr,"utf-8")

    i = i + 1

    loCompress.FirstChunk = 0
    IF (i = (lnNumBlocks - 1)) THEN
        loCompress.LastChunk = 1
    ENDIF

ENDDO

loFacSrc.FileClose()
loFacDest.FileClose()

* Examine the size of the restored file.
? "restored size: " + STR(loFac.FileSize(lcRestoredPath))

* Compare the contents of the original with the restored.
lnBEqualContents = loFac.FileContentsEqual(lcRestoredPath,lcOriginalPath)
? "Contents Equal: " + STR(lnBEqualContents)

RELEASE loCompress
RELEASE loFac
RELEASE loFacSrc
RELEASE loFacDest