#include <db_cxx.h>

void Db::set_msgcall(void (*db_msgcall_fcn)(const DbEnv *dbenv, char *msg));

There are interfaces in the Berkeley DB library which either directly output informational messages or statistical information, or configure the library to output such messages when performing other operations, for example, DbEnv::set_verbose and DbEnv::stat_print.

The DbEnv::set_msgcall and Db::set_msgcall methods are used to pass these messages to the application, and Berkeley DB will call db_msgcall_fcn with each message. It is up to the db_msgcall_fcn function to display the message in an appropriate manner.

Setting db_msgcall_fcn to NULL unconfigures the callback interface.

Alternatively, you can use the DbEnv::set_message_stream and Db::set_message_stream methods to display the messages via an output stream, or the Db::set_msgfile or DbEnv::set_msgfile methods to display the messages via a C library FILE *.

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

The Db::set_msgcall method configures operations performed using the specified Db handle, not all operations performed on the underlying database.

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

• The db_msgcall_fcn parameter is the application-specified message reporting function. The function takes two parameters:
  dbenv
  • The dbenv parameter is the enclosing database environment.
  msg
  • The msg parameter is the message string.
  
  

Berkeley DB is not re-entrant. Callback functions should not attempt to make library calls (for example, to release locks or close open handles). Re-entering Berkeley DB is not guaranteed to work correctly, and the results are undefined.