Library Version 18.1.40

Replacing Records Using Cursors
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## Replacing Records Using Cursors

You replace the data for a database record by using `DBC->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->get(cursorp, &key, &data, DB_SET);
    if (ret == 0) {
        data.data = replacement_data;
        data.size = strlen(replacement_data) + 1;
        cursorp->put(cursorp, &key, &data, DB_CURRENT);
    }

    /* Cursors must be closed */
    if (cursorp != NULL)
        cursorp->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.

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