#include <db.h>

void
DB->set_errcall(DB *, void (*db_errcall_fcn)
    (const DB_ENV *dbenv, const char *errpfx, const char *msg));  

When an error occurs in the Berkeley DB library, a Berkeley DB error 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 DB_ENV->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 DB->set_errfile() or DB->set_errfile() methods to display the additional information via a C library FILE *.

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 DB_ENV->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.