I am having problems with Qt qCompression

Can someone look at the code on this link. When I try to compress larger files, few GB nothing happens.

http://3adly.blogspot.com/2011/06/qt-folder-compression.html

I am trying to create an archive like tar in linux without a compression. Everything works with smaller files, but when I try to compress larger files nothing happens.

This is the code that I have used.

bool FolderCompressor::compressFolder(QString sourceFolder, QString destinationFile)
{
    QDir src(sourceFolder);
    if(!src.exists())//folder not found
    {
        return false;
    }

    file.setFileName(destinationFile);
    if(!file.open(QIODevice::WriteOnly))//could not open file
    {
        return false;
    }

    dataStream.setDevice(&file);

    bool success = compress(sourceFolder, "");
    file.close();

    return success;
}

bool FolderCompressor::compress(QString sourceFolder, QString prefex)
{
    QDir dir(sourceFolder);
    if(!dir.exists())
        return false;

    //1 - list all folders inside the current folder
    dir.setFilter(QDir::NoDotAndDotDot | QDir::Dirs);
    QFileInfoList foldersList = dir.entryInfoList();

    //2 - For each folder in list: call the same function with folders' paths
    for(int i=0; i<foldersList.length(); i++)
    {
        QString folderName = foldersList.at(i).fileName();
        QString folderPath = dir.absolutePath()+"/"+folderName;
        QString newPrefex = prefex+"/"+folderName;

        compress(folderPath, newPrefex);
    }

    //3 - List all files inside the current folder
    dir.setFilter(QDir::NoDotAndDotDot | QDir::Files);
    QFileInfoList filesList = dir.entryInfoList();

    //4- For each file in list: add file path and compressed binary data
    for(int i=0; i<filesList.length(); i++)
    {
        QFile file(dir.absolutePath()+"/"+filesList.at(i).fileName());
        if(!file.open(QIODevice::ReadOnly))//couldn't open file
        {
            return false;
        }

        dataStream << QString(prefex+"/"+filesList.at(i).fileName());
        dataStream << qCompress(file.readAll());

        file.close();
    }
 }


    return true;
}

I basically call compressFolder with source directory and destination compress file name.