Delphi ActiveX 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. Delphi ActiveX

var
success: Integer;
compress: TChilkatCompression;
fac: TCkFileAccess;
originalPath: WideString;
facSrc: TCkFileAccess;
facDest: TCkFileAccess;
blockSize: Integer;
numBlocks: Integer;
restoredPath: WideString;
decompressedStr: WideString;
compressedBytes: Array of Byte;
i: Integer;
bEqualContents: Integer;

begin
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:
compress := TChilkatCompression.Create(Self);
compress.Algorithm := 'deflate';

success := compress.CompressFile('qa_data/hamlet.xml','qa_data/hamlet_compressed.dat');
if (success = 0) then
  begin
    Memo1.Lines.Add(compress.LastErrorText);
    Exit;
  end;

fac := TCkFileAccess.Create(Self);

//  Examine the uncompressed and compressed sizes:
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.
Memo1.Lines.Add('uncompressed size: ' + IntToStr(fac.FileSize(originalPath)));
Memo1.Lines.Add('compressed size: ' + IntToStr(fac.FileSize('qa_data/hamlet_compressed.dat')));

//  Decompress in blocks..
facSrc := TCkFileAccess.Create(Self);
facDest := TCkFileAccess.Create(Self);

facSrc.OpenForRead('qa_data/hamlet_compressed.dat');

//  If we compress in 32K chunks, find out how many blocks there will be.
blockSize := 32768;
numBlocks := facSrc.GetNumBlocks(blockSize);

//  Open an output file for the decompressed data.
restoredPath := 'qa_output/hamlet_restored.xml';
success := facDest.OpenForWrite(restoredPath);
if (success = 0) then
  begin
    Memo1.Lines.Add(facDest.LastErrorText);
    Exit;
  end;

//  Assuming numBlocks > 1
compress.FirstChunk := 1;
compress.LastChunk := 0;

i := 0;
while i < numBlocks do
  begin
    compressedBytes := facSrc.ReadBlock(i,blockSize);
    decompressedStr := compress.DecompressString(compressedBytes);

    facDest.AppendText(decompressedStr,'utf-8');

    i := i + 1;

    compress.FirstChunk := 0;
    if (i = (numBlocks - 1)) then
      begin
        compress.LastChunk := 1;
      end;
  end;

facSrc.FileClose();
facDest.FileClose();

//  Examine the size of the restored file.
Memo1.Lines.Add('restored size: ' + IntToStr(fac.FileSize(restoredPath)));

//  Compare the contents of the original with the restored.
bEqualContents := fac.FileContentsEqual(restoredPath,originalPath);
Memo1.Lines.Add('Contents Equal: ' + IntToStr(Ord(bEqualContents)));