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You replace the data for a database record by using Dbc::put() with the DB_CURRENT flag.
#include <db_cxx.h> #include <string.h> ... Db my_database(NULL, 0); Dbc *cursorp; int ret; char *key1str = "My first string"; char *replacement_data = "replace me"; try { // Database open omitted // Get the cursor my_database.cursor(NULL, &cursorp, 0); // Set up our DBTs Dbt key(key1str, strlen(key1str) + 1); Dbt data; // Position the cursor */ ret = cursorp->get(&key, &data, DB_SET); if (ret == 0) { data.set_data(replacement_data); data.set_size(strlen(replacement_data) + 1); cursorp->put(&key, &data, DB_CURRENT); } } catch(DbException &e) { my_database.err(e.get_errno(), "Error!"); } catch(std::exception &e) { my_database.errx("Error! %s", e.what()); } // Cursors must be closed if (cursorp != NULL) cursorp->close(); my_database.close(0);
Note that you cannot change a record's key using this method; the key parameter is always ignored when you replace a record.
When replacing the data portion of a record, if you are replacing a record that is a member of a sorted duplicates set, then the replacement will be successful only if the new record sorts identically to the old record. This means that if you are replacing a record that is a member of a sorted duplicates set, and if you are using the default lexicographic sort, then the replacement will fail due to violating the sort order. However, if you provide a custom sort routine that, for example, sorts based on just a few bytes out of the data item, then potentially you can perform a direct replacement and still not violate the restrictions described here.
Under these circumstances, if you want to replace the data contained by a duplicate record, and you are not using a custom sort routine, then delete the record and create a new record with the desired key and data.