..
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   Copyright 1998-2021 Paulo Moura <pmoura@logtalk.org>
   SPDX-License-Identifier: Apache-2.0

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
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       http://www.apache.org/licenses/LICENSE-2.0

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.. index:: pair: encoding/1; Directive
.. _directives_encoding_1:

``encoding/1``
==============

Description
-----------

::

   encoding(Encoding)

Declares the source file text encoding. Requires a :term:`backend Prolog compiler`
supporting the chosen encoding. When used, this directive must be the first
term in the source file in the first line. This directive is also supported
in files included in a main file or in a dynamically created entity using
:ref:`directives_include_1` directives.

The encoding used in a source file (and, in the case of a Unicode
encoding, any BOM present) will be used for the intermediate Prolog
file generated by the compiler. Logtalk uses the encoding names specified by
`IANA <http://www.iana.org/assignments/character-sets/character-sets.xhtml>`_.
In those cases where a preferred MIME name alias is specified, the alias is
used instead. Examples includes ``'US-ASCII'``, ``'ISO-8859-1'``,
``'ISO-8859-2'``, ``'ISO-8859-15'``, ``'UCS-2'``, ``'UCS-2LE'``,
``'UCS-2BE'``, ``'UTF-8'``, ``'UTF-16'``, ``'UTF-16LE'``, ``'UTF-16BE'``,
``'UTF-32'``, ``'UTF-32LE'``, ``'UTF-32BE'``, ``'Shift_JIS'``, and
``'EUC-JP'``. When writing portable code that cannot be expressed using
ASCII, ``'UTF-8'`` is the most commonly supported Unicode encoding.

The backend Prolog compiler adapter files define a table that translates
between the Logtalk and Prolog specific atoms that represent each supported
encoding. The :ref:`encoding_directive <flag_encoding_directive>` read-only
flag can be used to find if a backend supports this directive and how.

Template and modes
------------------

::

   encoding(+atom)

Examples
--------

::

   :- encoding('UTF-8').
