void Db::set_error_stream(class ostream*);
When an error occurs in the Berkeley DB library, an exception is thrown or an errno value is returned by the method. 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_error_stream and Db::set_error_stream methods are used to enhance the mechanism for reporting error messages to the application by setting the C++ ostream used for displaying additional Berkeley DB error messages. In some cases, when an error occurs, Berkeley DB will output an additional error message to the specified stream.
The error message will consist of the prefix string and a colon (":") (if a prefix string was previously specified using DbEnv::set_errpfx), an error string, and a trailing <newline> character.
Alternatively, you can use the DbEnv::set_errfile method to display the additional information via a C library FILE *, or the DbEnv::set_errcall method to capture the additional error information in a way that does not use either output streams or C library FILE *'s. 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_error_stream method affects the entire environment and is equivalent to calling the DbEnv::set_error_stream method.
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