#include <db_cxx.h>
class Dbt { 
public: 
        Dbt(void *data, size_t size); 
        Dbt(); 
        Dbt(const Dbt &); 
        Dbt &operator = (const Dbt &); 
        ~Dbt();
        void *get_data() const; 
        void set_data(void *);
        u_int32_t get_size() const; 
        void set_size(u_int32_t);
        u_int32_t get_ulen() const; 
        void set_ulen(u_int32_t);
        u_int32_t get_dlen() const; 
        void set_dlen(u_int32_t);
        u_int32_t get_doff() const; 
        void set_doff(u_int32_t);
        u_int32_t get_flags() const; 
        void set_flags(u_int32_t);
        DBT *Dbt::get_DBT(); 
        const DBT *Dbt::get_const_DBT() const; 
        static Dbt *Dbt::get_Dbt(DBT *dbt); 
        static const Dbt *Dbt::get_const_Dbt(const DBT *dbt); 
}; 
      
        The Dbt class is used to encode key and data
        items in a Berkeley DB database.
    
        Storage and retrieval for the Db access methods are
        based on key/data pairs.  Both key and data items are represented by 
        
        
            Dbt objects.
        
        Key and data byte strings may refer to strings of zero length up to strings of essentially
        unlimited length. See Database limits for
        more information.
    
        
        
            In the case when the flags structure element is set to
            0,
        
            
        when the application is providing Berkeley DB a key or data item to store into the database,
        Berkeley DB expects the data 
        
        
            object
        
                
        to point to a byte string of size bytes. When returning a
        key/data item to the application, Berkeley DB will store into the data 
        
        
            object
        
        a pointer to a byte string of size bytes, 
        and the memory to which the pointer refers will be
        allocated and managed by Berkeley DB. Note that using the default flags
        for returned Dbts is only compatible with
        single threaded usage of Berkeley DB.
    
        Access to Dbt objects is not re-entrant. In particular, if multiple
        threads simultaneously access the same Dbt object using 
        Db API calls, the results are undefined, and may
        result in a crash.  One easy way to avoid problems is to use Dbt
        objects that are constructed as stack variables.
    
        Each Dbt object has an associated DBT struct,
        which is used by the underlying implementation of Berkeley DB and its C-language API. The
        Dbt::get_DBT()  method returns a pointer to this struct. Given a
        const Dbt object, Dbt::get_const_DBT()
        returns a const pointer to the same struct.
    
        Given a DBT struct, the Dbt::get_Dbt() method
        returns the corresponding Dbt object, if there is one. If the
        DBT object was not associated with a Dbt (that is,
        it was not returned from a call to Dbt::get_DBT()), then the
        result of Dbt::get_Dbt() is undefined. Given a const
        DBT struct, Dbt::get_const_Dbt() returns the
        associated const Dbt object, if there is one.
    
These methods may be useful for Berkeley DB applications including both C and C++ language software. It should not be necessary to use these calls in a purely C++ application.
                        Dbt::set_data(void *data)
                    
Set the data array.
                        The data parameter is an array
                        of bytes to be used to set the content for the
                        Dbt.
                    
                        Dbt::get_data()
                    
Return the data array.
                        Dbt::set_size(u_int32_t size)
                    
Sets the byte size of the data array, in bytes.
                        Dbt::get_size()
                    
Return the data array size.
                        Dbt::set_ulen(u_int32_t value)
                    
Set the byte size of the user-specified buffer.
                            Note that applications can determine the length of a record by setting
                            the ulen field to 0 and checking the return value in the 
                            size field. See
                            the DB_DBT_USERMEM flag for more information.
                    
                        Dbt::get_ulen()
                    
Return the length in bytes of the user-specified buffer.
                            Note that applications can determine the length of a record by setting
                            the ulen field to 0 and checking the return value in the 
                            size field. See
                            the DB_DBT_USERMEM flag for more information.
                    
                        Dbt::set_dlen(u_int32_t dlen)
                    
                        
                        
                            Set the
                        
                            length of the partial record being read or written by the
                            application, in bytes. See the DB_DBT_PARTIAL 
                            flag for more information.
                    
                         Dbt::get_dlen()
                    
Return the length of the partial record, in bytes.
                        Dbt::set_doff(u_int32_t value)
                    
                        
                        
                            Sets the
                        
                        offset of the partial record being read or written by the application,
                        in bytes. See the DB_DBT_PARTIAL flag for more information.
                    
                        Dbt::get_doff()
                    
Return the offset of the partial record, in bytes.
                        Dbt::set_flags(u_int32_t flags)
                    
Set the object flag value.
The flags parameter must be set to 0 or by bitwise inclusively OR'ing together one or more of the following values:
                            When this flag is set, Berkeley DB will allocate memory
                            for the returned key or data item (using 
                            malloc(3), or
                            the user-specified malloc function), and return a
                            pointer to it in the 
                            data field of the key or data 
                            DBT
                            structure. Because any allocated memory becomes the
                            responsibility of the calling application, the caller
                            must determine whether memory was allocated using the
                            returned value of the 
                            data field.
                    
                            It is an error to specify more than one of
                            DB_DBT_MALLOC, 
                            DB_DBT_REALLOC, and 
                            DB_DBT_USERMEM.
                    
When this flag is set Berkeley DB will allocate memory for the returned key or data item (using realloc(3), or the user-specified realloc function), and return a pointer to it in the data field of the key or data DBT structure. Because any allocated memory becomes the responsibility of the calling application, the caller must determine whether memory was allocated using the returned value of the data field.
                            It is an error to specify more than one of
                            DB_DBT_MALLOC, 
                            DB_DBT_REALLOC, and 
                            DB_DBT_USERMEM.
                    
                            The data
                            field of the key or data structure must refer
                            to memory that is at least 
                            ulen
                            bytes in length. If the
                            length of the requested item is less than or equal to
                            that number of bytes, the item is copied into the memory
                            to which the 
                            data
                            field refers. Otherwise, the 
                            size
                            field is set to the length needed for the requested
                            item, and the error 
                            DB_BUFFER_SMALL is returned. 
                    
                            It is an error to specify more than one of
                            DB_DBT_MALLOC, 
                            DB_DBT_REALLOC, and 
                            DB_DBT_USERMEM.
                    
                    If DB_DBT_MALLOC or
                    DB_DBT_REALLOC is specified, Berkeley DB
                    allocates a properly sized byte array to contain the data. This
                    can be convenient if you know little about the nature of the
                    data, specifically the size of data in the database. However, if
                    your application makes repeated calls to retrieve keys or data,
                    you may notice increased garbage collection due to this
                    allocation. If you know the maximum size of data you are
                    retrieving, you might decrease the memory burden and speed your
                    application by allocating your own byte array and using
                    DB_DBT_USERMEM. Even if you don't know the
                    maximum size, you can use this option and reallocate your array
                    whenever your retrieval API call returns an
                    DB_BUFFER_SMALL error or throws an exception
                    encapsulating an DB_BUFFER_SMALL.
                
Do partial retrieval or storage of an item. If the calling application is doing a get, the dlen bytes starting doff bytes from the beginning of the retrieved data record are returned as if they comprised the entire record. If any or all of the specified bytes do not exist in the record, the get is successful, and any existing bytes are returned.
For example, if the data portion of a retrieved record was 100 bytes, and a partial retrieval was done using a DBT having a dlen field of 20 and a doff field of 85, the get call would succeed, the data field would refer to the last 15 bytes of the record, and the size field would be set to 15.
If the calling application is doing a put, the dlen bytes starting doff bytes from the beginning of the specified key's data record are replaced by the data specified by the data and size structure elements. If dlen is smaller than size the record will grow; if dlen is larger than size the record will shrink. If the specified bytes do not exist, the record will be extended using nul bytes as necessary, and the put call will succeed.
It is an error to attempt a partial put using the Db::put() method in a database that supports duplicate records. Partial puts in databases supporting duplicate records must be done using a Dbc::put() method.
It is an error to attempt a partial put with differing dlen and size values in Queue or Recno databases with fixed-length records.
For example, if the data portion of a retrieved record was 100 bytes, and a partial put was done using a DBT having a dlen field of 20, a doff field of 85, and a size field of 30, the resulting record would be 115 bytes in length, where the last 30 bytes would be those specified by the put call.
                        This flag is ignored when used with the
                        pkey parameter on 
                        DB->pget() or
                        DBcursor->pget().
                    
                            After an application-supplied callback routine passed to
                            either 
                            Db::associate()
                            or 
                            Db::set_append_recno()
                            is executed, the 
                            data 
                            field of a DBT may refer to memory allocated with 
                            malloc(3)
                            or 
                            realloc(3). 
                            In that case,
                            the callback sets the 
                            DB_DBT_APPMALLOC 
                            flag in the DBT
                            so that Berkeley DB will call 
                            free(3)
                            to deallocate the
                            memory when it is no longer required.
                    
Set in a secondary key creation callback routine passed to Db::associate() to indicate that multiple secondary keys should be associated with the given primary key/data pair. If set, the size field indicates the number of secondary keys and the data field refers to an array of that number of DBT structures.
                            The DB_DBT_APPMALLOC flag may be set on any of the DBT
                            structures to indicate that their 
                            data 
                            field needs to be
                            freed.
                    
When this flag is set Berkeley DB will not write into the DBT. This may be set on key values in cases where the key is a static string that cannot be written and Berkeley DB might try to update it because the application has set a user defined comparison function.