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You replace the data for a database record by using DBC->c_put() with the DB_CURRENT flag.
#include <db.h> #include <string.h> ... DB *dbp; DBC *cursorp; DBT key, data; char *key1str = "My first string"; char *replacement_data = "replace me"; int ret; /* Initialize our DBTs. */ memset(&key, 0, sizeof(DBT)); memset(&data, 0, sizeof(DBT)); /* Set up our DBTs */ key.data = key1str; key.size = strlen(key1str) + 1; /* Database open omitted */ /* Get the cursor */ dbp->cursor(dbp, NULL, &cursorp, 0); /* Position the cursor */ ret = cursorp->c_get(cursorp, &key, &data, DB_SET); if (ret == 0) { data.data = replacement_data; data.size = strlen(replacement_data) + 1; cursorp->c_put(cursorp, &key, &data, DB_CURRENT); } /* Cursors must be closed */ if (cursorp != NULL) cursorp->c_close(cursorp); if (dbp != NULL) dbp->close(dbp, 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.