LevelDB数据库使用

向数据库插入数据的操作如下：

 leveldb::DB* LocalCacheDB:: m_pDB=NULL;
leveldb::Options LocalCacheDB:: m_options;

bool WriteToDB(INFO& info)
{
    leveldb::WriteOptions wo;
    leveldb::ReadOptions ro;
    wo.sync = false;//考虑是否异步

    //将info转为char[]
    int nLen = sizeof(INFO);
    char* chTmp = new char[nLen];
    ZeroMemory(chTmp, nLen);
    memcpy(chTmp,&info, nLen);

    char chKey[10];
    ZeroMemory(chKey, 10);

    leveldb::Iterator *iter = m_pDB->NewIterator(ro);
    if (iter == NULL)
    {
        return false;
    }
    iter->SeekToLast();//last的key最大,这里是自己定义的比较函数按key排序
    if (!iter->Valid())
    {
        //数据库为空
        itoa(1, chKey, 10);//key从1开始
    }
    else
    {
        leveldb::Slice sliceKey;
        sliceKey=iter->key();
        HPR_INT32 nKey=0;

        nKey=atoi(sliceKey.data());
        nKey++;
        itoa(nKey,chKey,10);
    }
    delete iter;//切忌在使用完sliceKey之前删除iter www.2cto.com

    leveldb::Status s = m_pDB->Put(wo,chKey,leveldb::Slice(chTmp,nLen));
    delete[] chTmp;
    if (!s.ok())
    {   

         return false;
    }
    cout<<"存入一条数据 index:"<<chKey<<endl;
    return true;
}

//比较函数如下:

class DBComparator:public leveldb::Comparator
{
    public:
    int Compare(const leveldb::Slice& a, const leveldb::Slice& b) const
    {
        int na,nb;
        na=atoi(a.data());
        nb=atoi(b.data());
        if (na<nb)
        {
            return -1;
        }
        if (na>nb)
        {
            return +1;
        }
        return 0;
    }
    // Ignore the following methods for now:
    const char* Name() const { return "DBComparator"; }
    void FindShortestSeparator(std::string*, const leveldb::Slice&) const { }
    void FindShortSuccessor(std::string*) const { }
};

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