181 lines
6.5 KiB
Plaintext
181 lines
6.5 KiB
Plaintext
[/==============================================================================
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Copyright (C) 2001-2011 Hartmut Kaiser
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Copyright (C) 2001-2011 Joel de Guzman
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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===============================================================================/]
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[section:stream Stream Parsers]
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This module includes the description of the different variants of the `stream`
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parser. It can be used to utilize existing streaming operators
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(`operator>>(std::istream&, ...)`) for input parsing.
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[heading Header]
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// forwards to <boost/spirit/home/qi/stream.hpp>
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#include <boost/spirit/include/qi_stream.hpp>
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Also, see __include_structure__.
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[section:stream Stream Parsers (`stream`, `wstream`, etc.)]
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[heading Description]
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The `stream_parser` is a primitive which allows to use pre-existing standard
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streaming operators for input parsing integrated with __qi__. It
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provides a wrapper parser dispatching the underlying input stream to the stream
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operator of the corresponding attribute type to be parsed. Any value `a` to be
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parsed using the `stream_parser` will result in invoking the standard streaming
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operator for its type `A`, for instance:
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std::istream& operator>> (std::istream&, A&);
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[heading Header]
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// forwards to <boost/spirit/home/qi/stream.hpp>
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#include <boost/spirit/include/qi_stream.hpp>
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Also, see __include_structure__.
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[heading Namespace]
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[table
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[[Name]]
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[[`boost::spirit::stream // alias: boost::spirit::qi::stream`]]
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[[`boost::spirit::wstream // alias: boost::spirit::qi::wstream`]]
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]
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[heading Synopsis]
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template <typename Char, typename Attrib>
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struct stream_parser;
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[heading Template parameters]
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[table
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[[Parameter] [Description] [Default]]
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[[`Char`] [The character type to use to generate
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the input. This type will be used while
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assigning the generated characters to the
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underlying input iterator.] [`char`]]
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[[`Attrib`] [The type of the attribute the `stream_parser` is
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expected to parse its input into.] [`spirit::basic_hold_any<Char>`]]
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]
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[heading Model of]
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[:__primitive_parser_concept__]
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[variablelist Notation
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[[`s`] [A variable instance of any type with a defined matching
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streaming `operator>>()` or a __qi_lazy_argument__ that
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evaluates to any type with a defined matching streaming
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`operator>>()`.]]
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]
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[heading Expression Semantics]
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Semantics of an expression is defined only where it differs from, or is
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not defined in __primitive_parser_concept__.
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[table
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[[Expression] [Description]]
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[[`stream`] [Call the streaming `operator>>()` for the type
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of the mandatory attribute. The input recognized
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by this operator will be the result of the
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`stream` parser. This parser never fails
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(unless the underlying input stream reports an
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error). The character type of the I/O istream
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is assumed to be `char`.]]
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[[`wstream`] [Call the streaming `operator>>()` for the type
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of the mandatory attribute. The input recognized
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by this operator will be the result of the
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`wstream` parser. This parser never fails
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(unless the underlying input stream reports an
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error). The character type of the I/O istream
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is assumed to be `wchar_t`.]]
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]
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All parsers listed in the table above are predefined specializations of the
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`stream_parser<Char>` basic stream parser type described below. It is
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possible to directly use this type to create stream parsers using an
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arbitrary underlying character type.
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[table
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[[Expression] [Semantics]]
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[
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[``stream_parser<
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Char, Attrib
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>()``] [Call the streaming `operator>>()` for the type
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of the optional attribute, `Attrib`. The input recognized
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by this operator will be the result of the
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`stream_parser<>` parser. This parser never fails
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(unless the underlying input stream reports an
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error). The character type of the I/O istream
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is assumed to be `Char`]]
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]
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[heading Additional Requirements]
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All of the stream parsers listed above require the type of the value to
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parse (the associated attribute) to implement a streaming operator conforming
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to the usual I/O streams conventions (where `attribute_type` is the type of the
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value to recognize while parse):
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template <typename Istream>
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Istream& operator>> (Istream& os, attribute_type& attr)
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{
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// type specific input parsing
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return os;
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}
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This operator will be called by the stream parsers to gather the input for
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the attribute of type `attribute_type`.
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[note If the `stream` parser is invoked inside a [qi_match `match`]
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(or [qi_match `phrase_match`]) stream manipulator the `Istream`
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passed to the `operator>>()` will have registered (imbued) the same
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standard locale instance as the stream the [qi_match `match`] (or
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[qi_match `phrase_match`]) manipulator has been used with.
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This ensures all facets registered (imbued) with the original I/O
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stream object are used during input parsing.
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]
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[heading Attributes]
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[table
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[[Expression] [Attribute]]
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[[`stream`] [`spirit::hold_any`]]
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[[`wstream`] [`spirit::whold_any`]]
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[[`stream_parser<Char, Attrib>()`] [`Attrib`]]
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]
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[important The attribute type `spirit::hold_any` exposed by some of the stream
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parsers is semantically and syntactically equivalent to
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the type implemented by __boost_any__. It has been added to /Spirit/
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as it has better performance and a smaller footprint than
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__boost_any__.
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]
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[heading Complexity]
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[:O(N), where N is the number of characters consumed by the stream parser]
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[heading Example]
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[note The test harness for the example(s) below is presented in the
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__qi_basics_examples__ section.]
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A class definition used in the examples:
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[reference_qi_complex]
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[reference_qi_stream_complex]
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[reference_qi_stream]
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[endsect]
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[endsect]
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