#include <db_cxx.h>
 
void Db::set_errcall(void (*db_errcall_fcn)
    (const DbEnv *dbenv, const char *errpfx, const char *msg));

When an error occurs in the Berkeley DB library, an exception is thrown or an error return value is returned by the interface. In some cases, however, the errno value may be insufficient to completely describe the cause of the error, especially during initial application debugging.

The DbEnv::set_errcall() and Db::set_errcall() methods are used to enhance the mechanism for reporting error messages to the application. In some cases, when an error occurs, Berkeley DB will call db_errcall_fcn() with additional error information. It is up to the db_errcall_fcn() function to display the error message in an appropriate manner.

Setting db_errcall_fcn to NULL unconfigures the callback interface.

Alternatively, you can use the DbEnv::set_error_stream() and Db::set_error_stream() methods to display the additional information via an output stream, or the Db::set_errfile() or Db::set_errfile() methods to display the additional information via a C library FILE *. You should not mix these approaches.

This error-logging enhancement does not slow performance or significantly increase application size, and may be run during normal operation as well as during application debugging.

For Db handles opened inside of Berkeley DB environments, calling the Db::set_errcall() method affects the entire environment and is equivalent to calling the DbEnv::set_errcall() method.

When used on a database that was not opened in an environment, the Db::set_errcall() method configures operations performed using the specified Db handle, not all operations performed on the underlying database.

The Db::set_errcall() method may be called at any time during the life of the application.