When an error occurs in the Berkeley DB library, a Berkeley DB error or an error
return value is returned by the function. 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->set_errcall function is 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. The
function must be declared with two arguments; the first will be the prefix
string (as previously set by DB->set_errpfx or
DBENV->set_errpfx), the second will be the error message string.
It is up to the db_errcall_fcn function to display the error
message in an appropriate manner.