(MFC) Decompress Large Text File in Blocks

Decompresses a large text file in blocks, and compares the restored (decompressed) file with the original to make sure it's correct.

Chilkat C/C++ Library Downloads MS Visual C/C++ Libs

See Also: Using MFC CString in Chilkat

#include <CkCompression.h>
#include <CkFileAccess.h>
#include <CkByteData.h>

void ChilkatSample(void)
    {
    CkString strOut;

    // 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:
    CkCompression compress;
    compress.put_Algorithm("deflate");

    bool success = compress.CompressFile("qa_data/hamlet.xml","qa_data/hamlet_compressed.dat");
    if (success != true) {
        strOut.append(compress.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    CkFileAccess fac;

    // Examine the uncompressed and compressed sizes:
    const char *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.
    strOut.append("uncompressed size: ");
    strOut.appendInt(fac.FileSize(originalPath));
    strOut.append("\r\n");
    strOut.append("compressed size: ");
    strOut.appendInt(fac.FileSize("qa_data/hamlet_compressed.dat"));
    strOut.append("\r\n");

    // Decompress in blocks..
    CkFileAccess facSrc;
    CkFileAccess facDest;

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

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

    // Open an output file for the decompressed data.
    const char *restoredPath = "qa_output/hamlet_restored.xml";
    success = facDest.OpenForWrite(restoredPath);
    if (success != true) {
        strOut.append(facDest.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    const char *decompressedStr = 0;
    CkByteData compressedBytes;

    int i = 0;
    while (i < numBlocks) {
        success = facSrc.ReadBlock(i,blockSize,compressedBytes);
        if (i == 0) {
            decompressedStr = compress.beginDecompressString(compressedBytes);
        }
        else {
            decompressedStr = compress.moreDecompressString(compressedBytes);
        }

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

        i = i + 1;
    }

    // At the very end, flush any remaining content, if any.
    decompressedStr = compress.endDecompressString();
    facDest.AppendText(decompressedStr,"utf-8");

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

    // Examine the size of the restored file.
    strOut.append("restored size: ");
    strOut.appendInt(fac.FileSize(restoredPath));
    strOut.append("\r\n");

    // Compare the contents of the original with the restored.
    bool bEqualContents = fac.FileContentsEqual(restoredPath,originalPath);
    strOut.append("Contents Equal: ");
    strOut.appendInt(bEqualContents);
    strOut.append("\r\n");


    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }