Pascal (Lazarus/Delphi)

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. Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.Compression,
  Chilkat.FileAccess;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  compress: TCompression;
  fac: TFileAccess;
  originalPath: string;
  facSrc: TFileAccess;
  facDest: TFileAccess;
  blockSize: Integer;
  numBlocks: Integer;
  restoredPath: string;
  decompressedStr: string;
  compressedBytes: TBytes;
  i: Integer;
  bEqualContents: Boolean;

begin
  success := False;

  //  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 := TCompression.Create;
  compress.Algorithm := 'deflate';

  success := compress.CompressFile('qa_data/hamlet.xml','qa_data/hamlet_compressed.dat');
  if (success = False) then
    begin
      WriteLn(compress.LastErrorText);
      Exit;
    end;

  fac := TFileAccess.Create;

  //  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.
  WriteLn('uncompressed size: ' + fac.FileSize(originalPath));
  WriteLn('compressed size: ' + fac.FileSize('qa_data/hamlet_compressed.dat'));

  //  Decompress in blocks..
  facSrc := TFileAccess.Create;
  facDest := TFileAccess.Create;

  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 = False) then
    begin
      WriteLn(facDest.LastErrorText);
      Exit;
    end;

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

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

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

  //  Examine the size of the restored file.
  WriteLn('restored size: ' + fac.FileSize(restoredPath));

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


  compress.Free;
  fac.Free;
  facSrc.Free;
  facDest.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.