Chapter 6. Db_multimap

Chapter 6. Db_multimap
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This class is the combination of std::multimap and hash_multimap.

By setting database handles as DB_BTREE or DB_HASH type respectively, you will be using an equivalent of std::multimap or hash_multimap respectively. Database(dbp) and environment(penv) handle requirement: The dbp handle must meet the following requirement: 1. Database type should be DB_BTREE or DB_HASH. 2. Either DB_DUP or DB_DUPSORT flag must be set. Note that so far Berkeley DB does not allow DB_DUPSORT be set and the database is storing identical key/data pairs, i.e. we can't store two (1, 2), (1, 2) pairs into a database D with DB_DUPSORT flag set, but only can do so with DB_DUP flag set; But we can store a (1, 2) pair and a (1, 3) pair into D with DB_DUPSORT flag set. So if your data set allows DB_DUPSORT flag, you should set it to gain a lot of performance promotion. 3. No DB_RECNUM flag set. 4. No DB_TRUNCATE specified in database open flags. 5. DB_THREAD must be set if you are sharing the database handle across multiple threads directly, or indirectly by sharing the container object across multiple threads.

Class Template Parameters

kdt

The key data type.

ddt

The data data type. db_multimap stores key/data pairs.

value_type_sub

Do not specify anything if ddt type is a class/struct type; Otherwise, specify ElementHolder<ddt> to it.

iterator_t

Never specify anything to this type parameter. It is only used internally.

Public Members

Member	Description
insert	Range insertion.
erase	Erase elements by key.
equal_range	Find the range within which all keys equal to specified key x.
equal_range_N	Find equal range and number of key/data pairs in the range.
count	Count the number of key/data pairs having specified key x.
upper_bound	Find the least key greater than x.
db_multimap	Constructor.
~db_multimap
operator=	Container content assignment operator.
swap	Swap content with another multimap container.
operator==	Returns whether the two containers have identical content.
operator!=	Container unequality comparison operator.

Group

Dbstl Container Classes

insert

Function Details

void insert(InputIterator first,
    InputIterator last)

Range insertion.

Insert a range [first, last) of key/data pairs into this container.

Parameters

last

The open boundary of the range.

first

The closed boundary of the range.

void insert(const_iterator &first,
    const_iterator &last)

Range insertion.

Insert a range [first, last) of key/data pairs into this container.

Parameters

last

The open boundary of the range.

first

The closed boundary of the range.

iterator insert(const value_type &x)

Insert a single key/data pair if the key is not in the container.

Parameters

x

The key/data pair to insert.

Return Value

A pair P, if insert OK, i.e. the inserted key wasn't in the container, P.first will be the iterator sitting on the inserted key/data pair, and P.second is true; otherwise P.first is an invalid iterator and P.second is false.

Group: Insert Functions

http://www.cplusplus.com/reference/stl/multimap/insert/

Class

db_multimap