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(Visual FoxPro) Decompress Large Text File in BlocksDecompresses 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.
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 |
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