Table of Contents
Cursors provide a mechanism by which you can iterate over the records in a database. Using cursors, you can get, put, and delete database records. If a database allows duplicate records, then cursors are the easiest way that you can access anything other than the first record for a given key.
This chapter introduces cursors. It explains how to open and close them, how to use them to modify databases, and how to use them with duplicate records.
Cursors are managed using the
DBC structure.
To use a cursor, you must open it using the
DB->cursor()
method.
For example:
#include <db.h> ... DB *my_database; DBC *cursorp; /* Database open omitted for clarity */ /* Get a cursor */ my_database->cursor(my_database, NULL, &cursorp, 0);
When you are done with the cursor, you should close it. To close a
cursor, call the
DBC->close()
method. Note that closing your database while cursors are still opened
within the scope of the DB handle, especially if those cursors are
writing to the database, can have unpredictable results.
It is recommended that you
close all cursor handles after their use to ensure concurrency and to release resources such as page locks.
#include <db.h>
...
DB *my_database;
DBC *cursorp;
/* Database and cursor open omitted for clarity */
if (cursorp != NULL)
cursorp->close(cursorp);
if (my_database != NULL)
my_database->close(my_database, 0);