C++

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. C++

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

void ChilkatSample(void)
    {
    bool 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:
    CkCompression compress;
    compress.put_Algorithm("deflate");

    success = compress.CompressFile("qa_data/hamlet.xml","qa_data/hamlet_compressed.dat");
    if (success == false) {
        std::cout << compress.lastErrorText() << "\r\n";
        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.
    std::cout << "uncompressed size: " << fac.FileSize(originalPath) << "\r\n";
    std::cout << "compressed size: " << fac.FileSize("qa_data/hamlet_compressed.dat") << "\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 == false) {
        std::cout << facDest.lastErrorText() << "\r\n";
        return;
    }

    const char *decompressedStr = 0;
    CkByteData compressedBytes;

    //  Assuming numBlocks > 1
    compress.put_FirstChunk(true);
    compress.put_LastChunk(false);

    int i = 0;
    while (i < numBlocks) {
        success = facSrc.ReadBlock(i,blockSize,compressedBytes);
        decompressedStr = compress.decompressString(compressedBytes);

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

        i = i + 1;

        compress.put_FirstChunk(false);
        if (i == (numBlocks - 1)) {
            compress.put_LastChunk(true);
        }

    }

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

    //  Examine the size of the restored file.
    std::cout << "restored size: " << fac.FileSize(restoredPath) << "\r\n";

    //  Compare the contents of the original with the restored.
    bool bEqualContents = fac.FileContentsEqual(restoredPath,originalPath);
    std::cout << "Contents Equal: " << bEqualContents << "\r\n";
    }