Library Version 18.1.40

Transactional Cursors
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## Transactional Cursors

You can transaction-protect your cursor operations by specifying a transaction handle at the time that you create your cursor. Beyond that, you do not ever provide a transaction handle directly to a cursor method.

Note that if you transaction-protect a cursor, then you must make sure that the cursor is closed before you either commit or abort the transaction. For example:

    #include "db_cxx.h"

    ...

    int main(void)
    {
        // Environment and database opens omitted
        ...

        DbTxn *txn = NULL;
        Dbc *cursorp = NULL;

        try {

            Dbt key, data;
            key.set_data(keystr);
            key.set_size((strlen(keystr) + 1) * sizeof(char));
            key.set_data(datastr);
            key.set_size((strlen(datastr) + 1) * sizeof(char));

            DbTxn *txn = NULL;
            myEnv.txn_begin(NULL, &txn, 0);
            try {
                // Get our cursor. Note that we pass the transaction handle
                // here.
                db.cursor(txn, &cursorp, 0);

                // Perform our operations. Note that we do not pass a
                // transaction handle here.
                char *replacementString = "new string";
                while (cursor->get(&key, &data, DB_NEXT) == 0) {
                    data.set_data(void *)replacementString);
                    data.set_size((strlen(replacementString) + 1) *
                        sizeof(char));
                    cursor->put(&key, &data, DB_CURRENT);
                }

                // We're done. Commit the transaction.
                cursor->close();
                txn->commit(0);
            } catch (DbException &e) {
                std::cerr << "Error in transaction: "
                           << e.what() << std::endl;
                cursor->close();
                txn->abort();
            }

        } catch(DbException &e) {
            std::cerr << "Error opening database and environment: "
                      << file_name << ", "
                      << envHome << std::endl;
            std::cerr << e.what() << std::endl;
        }

        return (EXIT_SUCCESS);
    }

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