Memory File helper for zlib compress

struct MemFile
{
    std::vector<unsigned char> bytes;
    std::vector<unsigned char> zip;
    void clear() { bytes.clear(); zip.clear(); }
    void pack()
    {
        int zip_size = bytes.size()*1.2;
        if (zip_size < 1000)
            zip_size = 1000;
        zip.resize(zip_size);
        unsigned int destLen;
        compress(&zip[0], (unsigned int*)&destLen, &bytes[0], (unsigned int)bytes.size());
        zip.resize(destLen);
    }
};

int fwrite(void *buffer, int size, int count, MemFile*f)
{
    int last_size = f->bytes.size();
    f->bytes.resize(last_size + size * count);
    memcpy(&(f->bytes[last_size]), buffer, size * count);
    return size * count;
}