#include <db.h>

void
DB_ENV->set_errcall(DB_ENV *dbenv, 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_ENV->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.

The DB_ENV->set_errcall method configures operations performed using the specified DB_ENV handle, not all operations performed on the underlying database environment.

The DB_ENV->set_errcall method may be called at any time during the life of the application.

• The db_errcall_fcn parameter is the application-specified error reporting function. The function takes three parameters:
  dbenv
  • The dbenv parameter is the enclosing database environment.
  errpfx
  • The errpfx parameter is the prefix string (as previously set by DB->set_errpfx or DB_ENV->set_errpfx).
  msg
  • The msg parameter is the error 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.