lmdb的一些库相关函数

它的作用是：打开一个环境handle。

注：如果函数失败，我们要调用 mdb_env_close() 来丢弃  MDB_env handle.

参数说明：

[in] env ：就是我们的环境handle。

[in] path :数据的路径。注意：它必须存在，并且可写；

[in] flags: 对于环境的一些特别的选项，它必须被设为0 或着把不同的选项 or在一起，

       常见的flag:http://104.237.133.194/doc/ group__mdb.html#ga32a193c6bf4d7d5c5d579e71f22e9340

[in] mode：对于linux来说 ，就是这个操作的对于文件权限(如：0644），windows忽略；

返回值：如果错误，返回一个非零的值，如果正确，返回零；

函数 ：mdb_env_close ()

void mdb_env_close ( MDB_env * env)

作用：Close the environment and release the memory map.

函数: int mdb_env_set_mapsize()

<span style="color: #0000ff">int</span> mdb_env_set_mapsize  ( MDB_env *<span style="color: #000000">  env,  
                            size_t    size  
                          )</span>

作用：设置环境的memory map 的大小；注意：默认大小 为：10485760 bytes，该函数用在mdb_env_create()之后，且mdb_env_open()之前，当然，在后面它也可能被调用的；

返回值：如果错误，返回一个非零的值，如果正确，返回零；

函数：int mdb_txn_begin()

<span style="color: #0000ff">int</span> mdb_txn_begin  ( MDB_env *<span style="color: #000000">     env,  
                     MDB_txn </span>*<span style="color: #000000">     parent,  
                     unsigned </span><span style="color: #0000ff">int</span><span style="color: #000000">  flags,  
                     MDB_txn </span>**<span style="color: #000000">     txn  
                    )</span>

 

作用：Create a transaction for use with the environment.

参数：[in] env：An environment handle returned by mdb_env_create() 

         [in] parent：可以为空，即NULL，如果不是空的话，the new transaction will be a nested transaction。

         [in] flags： 指对于操作来说一些特别的选项，可以为0或着其它：如MDB_RDONLY,表示：它不会执行任何写操作；

        [in] txn  ,Address where the new MDB_txn handle will be stored .

返回值：如果错误，返回一个非零的值，如果正确，返回零；

另外：The transaction handle may be discarded using mdb_txn_abort() or mdb_txn_commit().

函数：mdb_dbi_open()

<span style="color: #0000ff">int</span> mdb_dbi_open  ( MDB_txn *<span style="color: #000000">  txn,  
  </span><span style="color: #0000ff">const</span> <span style="color: #0000ff">char</span> *<span style="color: #000000">  name,  
  unsigned </span><span style="color: #0000ff">int</span><span style="color: #000000">  flags,  
  MDB_dbi </span>*<span style="color: #000000">  dbi  
 )</span>

 

作用：在环境里打开一个database；

注意：database handle denotes the name and parameters of a database, independently of whether such a database exists.The database handle may be discarded by calling mdb_dbi_close().

参数：

[in] txn ：A transaction 的handle；

[in]  name：打开的database的名字，If only a single database is needed in the environment, this value may be NULL.

[in]  flags：Special options for this database. 可以为0或着其它选项

[out] dbi ：Address where the new MDB_dbi handle will be store；

返回值：如果错误，返回一个非零的值，如果正确，返回零；

函数：int mdb_put()

<span style="color: #0000ff">int</span> mdb_put  ( MDB_txn *<span style="color: #000000">  txn,  
  MDB_dbi  dbi,  
  MDB_val </span>*<span style="color: #000000">  key,  
  MDB_val </span>*<span style="color: #000000">  data,  
  unsigned </span><span style="color: #0000ff">int</span><span style="color: #000000">  flags  
 )</span>

作用：store items into a datagase，也就是说，把key/data pairs存放到database里面。

注意：当键值有相同的时候，The default behavior is to enter the new key/data pair, replacing any previously existing

key if duplicates are disallowed, or adding a duplicate data item if duplicates are allowed 。

参数：

[in] txn： A transaction handle returned by mdb_txn_begin() 
[in] dbi ：A database handle returned by mdb_dbi_open() 
[in] key ：The key to store in the database 
[in,out] data： The data to store 
[in] flags Special options for this operation. This parameter must be set to 0 or by bitwise OR‘ing together one or more of the values described here.

返回值：如果错误，返回一个非零的值，如果正确，返回零；

 

函数：int mdb_txn_commit()

<span style="color: #0000ff">int</span> mdb_txn_commit  ( MDB_txn *  txn )

作用：提交所有的操作：Commit all the operations of a transaction into the database.

注意：提交完以后，The transaction handle is freed. It and its cursors must not be used again after this call, except with mdb_cursor_renew().

参数：[in] txn:即我们要提交的那个transaction的handle;

返回值：如果错误，返回一个非零的值，如果正确，返回零；

 

函数：int mdb_cursor_open （）

<span style="color: #0000ff">int</span> mdb_cursor_open  ( MDB_txn *<span style="color: #000000">  txn,  
  MDB_dbi  dbi,  
  MDB_cursor </span>**<span style="color: #000000">  cursor  
 )</span>

作用：创建一个cursor的handle。

备注：A cursor is associated with a specific transaction and database。

参数：

[<span style="color: #0000ff">in</span><span style="color: #000000">] txn A transaction handle returned by mdb_txn_begin()  
[</span><span style="color: #0000ff">in</span><span style="color: #000000">] dbi A database handle returned by mdb_dbi_open()  
[</span><span style="color: #0000ff">out</span>] cursor Address <span style="color: #0000ff">where</span> the <span style="color: #0000ff">new</span> MDB_cursor handle will be stored

返回值：如果错误，返回一个非零的值，如果正确，返回零；

函数：mdb_cursor_get()

<span style="color: #0000ff">int</span> mdb_cursor_get  ( MDB_cursor *<span style="color: #000000">  cursor,  
  MDB_val </span>*<span style="color: #000000">  key,  
  MDB_val </span>*<span style="color: #000000">  data,  
  MDB_cursor_op  op  
 )</span>

功能：通过cursor恢复数据

参数：

[<span style="color: #0000ff">in</span><span style="color: #000000">] cursor： A cursor handle returned by mdb_cursor_open()  
[</span><span style="color: #0000ff">in</span>,<span style="color: #0000ff">out</span>] key： The key <span style="color: #0000ff">for</span><span style="color: #000000"> a retrieved item  
[</span><span style="color: #0000ff">in</span>,<span style="color: #0000ff">out</span><span style="color: #000000">] data： The data of a retrieved item  
[</span><span style="color: #0000ff">in</span>] op： A cursor operation MDB_cursor_op

其中：enum MDB_cursor_op，它枚举了许多Cursor Get 的操作，如下所示：

<span style="color: #000000">MDB_FIRST  
Position at first key</span>/<span style="color: #000000">data item 
 
MDB_FIRST_DUP  
Position at first data item of current key. Only </span><span style="color: #0000ff">for</span><span style="color: #000000"> MDB_DUPSORT 
 
MDB_GET_BOTH  
Position at key</span>/data pair. Only <span style="color: #0000ff">for</span><span style="color: #000000"> MDB_DUPSORT 
 
MDB_GET_BOTH_RANGE  
position at key, nearest data. Only </span><span style="color: #0000ff">for</span><span style="color: #000000"> MDB_DUPSORT 
 
MDB_GET_CURRENT  
Return key</span>/<span style="color: #000000">data at current cursor position 
 
MDB_GET_MULTIPLE  
Return key and up to a page of duplicate data items </span><span style="color: #0000ff">from</span> current cursor position. Move cursor to prepare <span style="color: #0000ff">for</span> MDB_NEXT_MULTIPLE. Only <span style="color: #0000ff">for</span><span style="color: #000000"> MDB_DUPFIXED 
 
MDB_LAST  
Position at last key</span>/<span style="color: #000000">data item 
 
MDB_LAST_DUP  
Position at last data item of current key. Only </span><span style="color: #0000ff">for</span><span style="color: #000000"> MDB_DUPSORT 
 
MDB_NEXT  
Position at next data item 
 
MDB_NEXT_DUP  
Position at next data item of current key. Only </span><span style="color: #0000ff">for</span><span style="color: #000000"> MDB_DUPSORT 
 
MDB_NEXT_MULTIPLE  
Return key and up to a page of duplicate data items </span><span style="color: #0000ff">from</span> next cursor position. Move cursor to prepare <span style="color: #0000ff">for</span> MDB_NEXT_MULTIPLE. Only <span style="color: #0000ff">for</span><span style="color: #000000"> MDB_DUPFIXED 
 
MDB_NEXT_NODUP  
Position at first data item of next key 
 
MDB_PREV  
Position at previous data item 
 
MDB_PREV_DUP  
Position at previous data item of current key. Only </span><span style="color: #0000ff">for</span><span style="color: #000000"> MDB_DUPSORT 
 
MDB_PREV_NODUP  
Position at last data item of previous key 
 
MDB_SET  
Position at specified key 
 
MDB_SET_KEY  
Position at specified key, </span><span style="color: #0000ff">return</span> key +<span style="color: #000000"> data 
 
MDB_SET_RANGE  
Position at first key greater than or equal to specified key.</span>

先写到这里吧。。

看的时候，可以结合一个例子：http://blog.csdn.net/u012235274/article/details/51899598

还有很多：http://104.237.133.194/doc/index.html

lmdb的一些库相关函数

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