PowerBuilder Requires Chilkat v11.0.0+

Decompress Large Text File in Blocks

See more Compression Examples

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

integer li_rc
integer li_Success
oleobject loo_Compress
oleobject loo_Fac
string ls_OriginalPath
oleobject loo_FacSrc
oleobject loo_FacDest
integer li_BlockSize
integer li_NumBlocks
string ls_RestoredPath
string ls_DecompressedStr
integer i
integer li_BEqualContents

li_Success = 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:
loo_Compress = create oleobject
li_rc = loo_Compress.ConnectToNewObject("Chilkat.Compression")
if li_rc < 0 then
    destroy loo_Compress
    MessageBox("Error","Connecting to COM object failed")
    return
end if
loo_Compress.Algorithm = "deflate"

li_Success = loo_Compress.CompressFile("qa_data/hamlet.xml","qa_data/hamlet_compressed.dat")
if li_Success = 0 then
    Write-Debug loo_Compress.LastErrorText
    destroy loo_Compress
    return
end if

loo_Fac = create oleobject
li_rc = loo_Fac.ConnectToNewObject("Chilkat.FileAccess")

//  Examine the uncompressed and compressed sizes:
ls_OriginalPath = "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.
Write-Debug "uncompressed size: " + string(loo_Fac.FileSize(ls_OriginalPath))
Write-Debug "compressed size: " + string(loo_Fac.FileSize("qa_data/hamlet_compressed.dat"))

//  Decompress in blocks..
loo_FacSrc = create oleobject
li_rc = loo_FacSrc.ConnectToNewObject("Chilkat.FileAccess")

loo_FacDest = create oleobject
li_rc = loo_FacDest.ConnectToNewObject("Chilkat.FileAccess")

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

//  If we compress in 32K chunks, find out how many blocks there will be.
li_BlockSize = 32768
li_NumBlocks = loo_FacSrc.GetNumBlocks(li_BlockSize)

//  Open an output file for the decompressed data.
ls_RestoredPath = "qa_output/hamlet_restored.xml"
li_Success = loo_FacDest.OpenForWrite(ls_RestoredPath)
if li_Success = 0 then
    Write-Debug loo_FacDest.LastErrorText
    destroy loo_Compress
    destroy loo_Fac
    destroy loo_FacSrc
    destroy loo_FacDest
    return
end if

//  Assuming numBlocks > 1
loo_Compress.FirstChunk = 1
loo_Compress.LastChunk = 0

i = 0
do while i < li_NumBlocks
    loo_CompressedBytes = loo_FacSrc.ReadBlock(i,li_BlockSize)
    ls_DecompressedStr = loo_Compress.DecompressString(loo_CompressedBytes)

    loo_FacDest.AppendText(ls_DecompressedStr,"utf-8")

    i = i + 1

    loo_Compress.FirstChunk = 0
    if i = (li_NumBlocks - 1) then
        loo_Compress.LastChunk = 1
    end if

loop

loo_FacSrc.FileClose()
loo_FacDest.FileClose()

//  Examine the size of the restored file.
Write-Debug "restored size: " + string(loo_Fac.FileSize(ls_RestoredPath))

//  Compare the contents of the original with the restored.
li_BEqualContents = loo_Fac.FileContentsEqual(ls_RestoredPath,ls_OriginalPath)
Write-Debug "Contents Equal: " + string(li_BEqualContents)


destroy loo_Compress
destroy loo_Fac
destroy loo_FacSrc
destroy loo_FacDest