Visual FoxPro

Compress Large Binary File in Blocks

See more Compression Examples

Compresses a large binary file in blocks. Visual FoxPro

LOCAL lnSuccess
LOCAL loFacSrc
LOCAL loFacDest
LOCAL lnBlockSize
LOCAL lnNumBlocks
LOCAL loCompress
LOCAL loFileBytes
LOCAL loCompressedBytes
LOCAL i

lnSuccess = 0

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

loFacSrc = CreateObject('Chilkat.FileAccess')
loFacDest = CreateObject('Chilkat.FileAccess')

* Open a large binary file for reading.
lnSuccess = loFacSrc.OpenForRead("qa_data/bmp/big.bmp")
IF (lnSuccess = 0) THEN
    ? loFacSrc.LastErrorText
    RELEASE loFacSrc
    RELEASE loFacDest
    CANCEL
ENDIF

* If we compress in 64K chunks, find out how many blocks there will be.
lnBlockSize = 65536
lnNumBlocks = loFacSrc.GetNumBlocks(lnBlockSize)

* Open an output file for the compressed data.
lnSuccess = loFacDest.OpenForWrite("c:/temp/qa_output/compressedBmp.dat")
IF (lnSuccess = 0) THEN
    ? loFacDest.LastErrorText
    RELEASE loFacSrc
    RELEASE loFacDest
    CANCEL
ENDIF

loCompress = CreateObject('Chilkat.Compression')
loCompress.Algorithm = "deflate"

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

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

    loFacDest.FileWrite(loCompressedBytes)

    i = i + 1

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

ENDDO

loFacSrc.FileClose()
loFacDest.FileClose()

? "Finished compressing file."

RELEASE loFacSrc
RELEASE loFacDest
RELEASE loCompress