59 lines
2.3 KiB
ReStructuredText
59 lines
2.3 KiB
ReStructuredText
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.. _implementation-defined-behavior:
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===============================
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Implementation-defined behavior
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===============================
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Contains the implementation details of the implementation-defined behavior in
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libc++. Implementation-defined is mandated to be documented by the Standard.
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.. note:
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This page is far from complete.
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Implementation-defined behavior
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===============================
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Updating the Time Zone Database
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-------------------------------
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The Standard allows implementations to automatically update the
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*remote time zone database*. Libc++ opts not to do that. Instead calling
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- ``std::chrono::remote_version()`` will update the version information of the
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*remote time zone database*,
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- ``std::chrono::reload_tzdb()``, if needed, will update the entire
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*remote time zone database*.
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This offers a way for users to update the *remote time zone database* and
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give them full control over the process.
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`[ostream.formatted.print]/3 <http://eel.is/c++draft/ostream.formatted.print#3>`_ A terminal capable of displaying Unicode
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--------------------------------------------------------------------------------------------------------------------------
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The Standard specifies that the manner in which a stream is determined to refer
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to a terminal capable of displaying Unicode is implementation-defined. This is
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used for ``std::print`` and similar functions taking an ``ostream&`` argument.
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Libc++ determines that a stream is Unicode-capable terminal by:
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* First it determines whether the stream's ``rdbuf()`` has an underlying
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``FILE*``. This is ``true`` in the following cases:
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* The stream is ``std::cout``, ``std::cerr``, or ``std::clog``.
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* A ``std::basic_filebuf<CharT, Traits>`` derived from ``std::filebuf``.
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* The way to determine whether this ``FILE*`` refers to a terminal capable of
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displaying Unicode is the same as specified for `void vprint_unicode(FILE*
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stream, string_view fmt, format_args args);
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<http://eel.is/c++draft/print.fun#7>`_. This function is used for other
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``std::print`` overloads that don't take an ``ostream&`` argument.
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Listed in the index of implementation-defined behavior
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======================================================
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The order of the entries matches the entries in the
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`draft of the Standard <http://eel.is/c++draft/impldefindex>`_.
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