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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); }