curget.so

berkeley db 4.6.21的源码。berkeley db是一个简单的数据库管理系统

m4_comment([$Id: curget.so,v 10.20 2003/10/18 19:15:52 bostic Exp $])

m4_ref_title(Access Methods, Retrieving records with a cursor,
    [@retrieving records with a cursor, retrieving records with a @cursor],
    am/cursor, am/curput)

m4_p([dnl
The m4_refT(dbc_get) retrieves records from the database using a cursor.
The m4_refT(dbc_get) takes a flag which controls how the cursor is
positioned within the database and returns the key/data item associated
with that positioning.  Similar to m4_ref(dbh_get), m4_ref(dbc_get) may
also take a supplied key and retrieve the data associated with that key
from the database.  There are several flags that you can set to
customize retrieval.])

m4_section(Cursor position flags)

m4_tagbegin

m4_tag([m4_ref(DB_FIRST), m4_ref(DB_LAST)], [dnl
Return the first (last) record in the database.])

m4_tag([m4_ref(DB_NEXT), m4_ref(DB_PREV)], [dnl
Return the next (previous) record in the database.])

m4_tag([m4_ref(DB_NEXT_DUP)], [dnl
Return the next record in the database, if it is a duplicate data item
for the current key.])

m4_tag([m4_ref(DB_NEXT_NODUP), m4_ref(DB_PREV_NODUP)], [dnl
Return the next (previous) record in the database that is not a
duplicate data item for the current key.])

m4_tag([m4_ref(DB_CURRENT)], [dnl
Return the record from the database to which the cursor currently refers.])

m4_tagend

m4_section(Retrieving specific key/data pairs)

m4_tagbegin

m4_tag([m4_ref(DB_SET)], [dnl
Return the record from the database that matches the supplied key.  In
the case of duplicates the first duplicate is returned and the cursor
is positioned at the beginning of the duplicate list.  The user can then
traverse the duplicate entries for the key.])

m4_tag([m4_ref(DB_SET_RANGE)], [dnl
Return the smallest record in the database greater than or equal to the
supplied key.  This functionality permits partial key matches and range
searches in the Btree access method.])

m4_tag([m4_ref(DB_GET_BOTH)], [dnl
Return the record from the database that matches both the supplied key
and data items.  This is particularly useful when there are large
numbers of duplicate records for a key, as it allows the cursor to
easily be positioned at the correct place for traversal of some part of
a large set of duplicate records.])

m4_tag([m4_ref(DB_GET_BOTH_RANGE)], [dnl
Return the smallest record in the database greater than or equal to the
supplied key and data items.])

m4_tagend

m4_section(Retrieving based on record numbers)

m4_tagbegin

m4_tag([m4_ref(DB_SET_RECNO)], [dnl
If the underlying database is a Btree, and was configured so that it is
possible to search it by logical record number, retrieve a specific
record based on a record number argument.])

m4_tag([m4_ref(DB_GET_RECNO)], [dnl
If the underlying database is a Btree, and was configured so that it is
possible to search it by logical record number, return the record number
for the record to which the cursor refers.])

m4_tagend

m4_section(Special-purpose flags)

m4_tagbegin

m4_tag([m4_ref(DB_CONSUME)], [dnl
Read-and-delete: the first record (the head) of the queue is returned and
deleted.  The underlying database must be a Queue.])

m4_tag([m4_ref(DB_RMW)], [dnl
Read-modify-write: acquire write locks instead of read locks during
retrieval. This can enhance performance in threaded applications by
reducing the chance of deadlock.])

m4_tagend

m4_p([dnl
In all cases, the cursor is repositioned by a m4_ref(dbc_get) operation
to point to the newly-returned key/data pair in the database.])

m4_p([dnl
The following is a code example showing a cursor walking through a
database and displaying the records it contains to the standard
output:])

include(ref/am/curget.cs)

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