Db::err()
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## Db::err()

    #include <db_cxx.h>

    Db::err(int error, const char *fmt, ...);

    Db::errx(const char *fmt, ...);

The DbEnv::err(), `DbEnv::errx()`, `Db::err()` and `Db::errx()` methods provide error-messaging functionality for applications written using the Berkeley DB library.

The `Db::err()` and DbEnv::err() methods construct an error message consisting of the following elements:

- An optional prefix string

  If no error callback function 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, in which the ANSI C X3.159-1989 (ANSI C) printf function specifies how subsequent parameters 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.

The `Db::errx()` and `DbEnv::errx()` methods are the same as the `Db::err()` and DbEnv::err() methods, except they do not append the final separator characters and standard error string to the error message.

This constructed error message is then handled as follows:

- If an error callback function has been set (see Db::set_errcall() and DbEnv::set_errcall()), that function is called with two parameters: any prefix string specified (see Db::set_errpfx() and DbEnv::set_errpfx()) and the error message.

- 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() and Db::set_error_stream()), the error message is written to that stream.

- If none of these output options have been configured, the error message is written to stderr, the standard error output stream.

### Parameters

#### error

The error parameter is the error value for which the DbEnv::err() and `Db::err()` methods will display an explanatory string.

#### fmt

The fmt parameter is an optional printf-style message to display.

### Class

Db

### See Also

Database and Related Methods

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