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(Delphi ActiveX) 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.
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; |
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