boost_1_45_0/libs/spirit/doc/qi/stream.qbk

[/==============================================================================
    Copyright (C) 2001-2010 Hartmut Kaiser
    Copyright (C) 2001-2010 Joel de Guzman

    Distributed under the Boost Software License, Version 1.0. (See accompanying
    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
===============================================================================/]

[section Stream]

This module includes the description of the different variants of the `stream` 
parser. It can be used to utilize existing streaming operators 
(`operator>>(std::istream&, ...)`) for input parsing.

[heading Header]

    // forwards to <boost/spirit/home/qi/stream.hpp>
    #include <boost/spirit/include/qi_stream.hpp>

Also, see __include_structure__.

[section:stream Stream (`stream`, `wstream`, etc.)]

[heading Description]

The `stream_parser` is a primitive which allows to use pre-existing standard
streaming operators for input parsing integrated with __qi__. It 
provides a wrapper parser dispatching the underlying input stream to the stream 
operator of the corresponding attribute type to be parsed. Any value `a` to be 
parsed using the `stream_parser` will result in invoking the standard streaming 
operator for its type `A`, for instance:

    std::istream& operator>> (std::istream&, A&);

[heading Header]

    // forwards to <boost/spirit/home/qi/stream.hpp>
    #include <boost/spirit/include/qi_stream.hpp>

Also, see __include_structure__.

[heading Namespace]

[table
    [[Name]]
    [[`boost::spirit::stream  // alias: boost::spirit::qi::stream`]]
    [[`boost::spirit::wstream // alias: boost::spirit::qi::wstream`]]
]

[heading Synopsis]

    template <typename Char, typename Attrib>
    struct stream_parser;

[heading Template parameters]

[table
    [[Parameter]    [Description]                       [Default]]
    [[`Char`]   [The character type to use to generate 
                 the input. This type will be used while 
                 assigning the generated characters to the 
                 underlying input iterator.]           [`char`]]
    [[`Attrib`] [The type of the attribute the `stream_parser` is
                 expected to parse its input into.]    [`spirit::hold_any`]]
]

[heading Model of]

[:__primitive_parser_concept__]

[variablelist Notation
    [[`s`]      [A variable instance of any type with a defined matching 
                 streaming `operator>>()` or a __qi_lazy_argument__ that 
                 evaluates to any type with a defined matching streaming 
                 `operator>>()`.]]
]

[heading Expression Semantics]

Semantics of an expression is defined only where it differs from, or is
not defined in __primitive_parser_concept__.

[table
    [[Expression]           [Description]]
    [[`stream`]             [Call the streaming `operator>>()` for the type
                             of the mandatory attribute. The input recognized 
                             by this operator will be the result of the 
                             `stream` parser. This parser never fails 
                             (unless the underlying input stream reports an 
                             error). The character type of the I/O istream
                             is assumed to be `char`.]]
    [[`wstream`]            [Call the streaming `operator>>()` for the type
                             of the mandatory attribute. The input recognized 
                             by this operator will be the result of the 
                             `wstream` parser. This parser never fails 
                             (unless the underlying input stream reports an 
                             error). The character type of the I/O istream
                             is assumed to be `wchar_t`.]]
]

All parsers listed in the table above are predefined specializations of the 
`stream_parser<Char>` basic stream parser type described below. It is 
possible to directly use this type to create stream parsers using an 
arbitrary underlying character type.

[table
    [[Expression]       [Semantics]]
    [
[``stream_parser<
    Char, Attrib
>()``]                      [Call the streaming `operator>>()` for the type
                             of the optional attribute, `Attrib`. The input recognized 
                             by this operator will be the result of the 
                             `stream_parser<>` parser. This parser never fails 
                             (unless the underlying input stream reports an 
                             error). The character type of the I/O istream
                             is assumed to be `Char`]]
]

[heading Additional Requirements]

All of the stream parsers listed above require the type of the value to 
parse (the associated attribute) to implement a streaming operator conforming 
to the usual I/O streams conventions (where `attribute_type` is the type of the 
value to recognize while parse):

    template <typename Istream>
    Istream& operator>> (Istream& os, attribute_type& attr)
    {
        // type specific input parsing
        return os;
    }

This operator will be called by the stream parsers to gather the input for
the attribute of type `attribute_type`. 

[note   If the `stream` parser is invoked inside a [qi_match `match`] 
        (or [qi_match `phrase_match`]) stream manipulator the `Istream` 
        passed to the `operator>>()` will have registered (imbued) the same 
        standard locale instance as the stream the [qi_match `match`] (or 
        [qi_match `phrase_match`]) manipulator has been used with. 
        This ensures all facets registered (imbued) with the original I/O 
        stream object are used during input parsing.
]

[heading Attributes]

[table
    [[Expression]           [Attribute]]
    [[`stream`]             [`spirit::hold_any`]]
    [[`wstream`]            [`spirit::hold_any`]]
    [[`stream_parser<Char, Attrib>()`]    [`Attrib`]]
]

[important The attribute type `spirit::hold_any` exposed by some of the stream 
           parsers is semantically and syntactically equivalent to 
           the type implemented by __boost_any__. It has been added to /Spirit/ 
           as it has better performance and a smaller footprint than 
           __boost_any__.
]

[heading Complexity]

[:O(N), where N is the number of characters consumed by the stream parser]

[heading Example]

[note The test harness for the example(s) below is presented in the
__qi_basics_examples__ section.]

A class definition used in the examples:

[reference_qi_complex]
[reference_qi_stream_complex]

[reference_qi_stream]

[endsect]

[endsect]