The DbEnv::err, DbEnv::errx, Db::err and
Db::errx methods provide error messaging functionality for
applications written using the Berkeley DB library.
The DbEnv::err method constructs an error message consisting of the
following elements:
An optional prefix string
If no error callback method has been set using the
DbEnv::set_errcall method, any prefix string specified using the
DbEnv::set_errpfx method, followed by two separating characters: a colon
and a <space> character.
An optional printf-style message
The supplied message fmt, if non-NULL, where the ANSI C X3.159-1989 (ANSI C)
printf function specifies how subsequent arguments are converted for
output.
A separator
Two separating characters: a colon and a <space> character.
A standard error string
The standard system or Berkeley DB library error string associated with the
error value, as returned by the DbEnv::strerror method.
This constructed error message is then handled as follows:
If a C library FILE * has been set (see Db::set_errfile and
DbEnv::set_errfile), the error message is written to that output
stream.
If a C++ ostream has been set
(see DbEnv::set_error_stream), the error message is written to that
stream.
If none of these output options has been configured, the error message
is written to stderr, the standard error output stream.
The DbEnv::errx and Db::errx methods perform identically to the
DbEnv::err and Db::err methods except that they do not append
the final separator characters and standard error string to the error
message.