Delphi ActiveX

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

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Chilkat_TLB;

...

procedure TForm1.Button1Click(Sender: TObject);
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)));
end;