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#

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:
Chilkat.Compression compress = new Chilkat.Compression();
compress.Algorithm = "deflate";

success = compress.CompressFile("qa_data/hamlet.xml","qa_data/hamlet_compressed.dat");
if (success == false) {
    Debug.WriteLine(compress.LastErrorText);
    return;
}

Chilkat.FileAccess fac = new Chilkat.FileAccess();

// Examine the uncompressed and compressed sizes:
string 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.
Debug.WriteLine("uncompressed size: " + Convert.ToString(fac.FileSize(originalPath)));
Debug.WriteLine("compressed size: " + Convert.ToString(fac.FileSize("qa_data/hamlet_compressed.dat")));

// Decompress in blocks..
Chilkat.FileAccess facSrc = new Chilkat.FileAccess();
Chilkat.FileAccess facDest = new Chilkat.FileAccess();

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.
string restoredPath = "qa_output/hamlet_restored.xml";
success = facDest.OpenForWrite(restoredPath);
if (success == false) {
    Debug.WriteLine(facDest.LastErrorText);
    return;
}

string decompressedStr;
byte[] compressedBytes = null;

// Assuming numBlocks > 1
compress.FirstChunk = true;
compress.LastChunk = false;

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

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

    i = i + 1;

    compress.FirstChunk = false;
    if (i == (numBlocks - 1)) {
        compress.LastChunk = true;
    }

}

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

// Examine the size of the restored file.
Debug.WriteLine("restored size: " + Convert.ToString(fac.FileSize(restoredPath)));

// Compare the contents of the original with the restored.
bool bEqualContents = fac.FileContentsEqual(restoredPath,originalPath);
Debug.WriteLine("Contents Equal: " + Convert.ToString(bEqualContents));