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[/==============================================================================
Copyright (C) 2001-2011 Joel de Guzman
Copyright (C) 2001-2011 Hartmut Kaiser
Copyright (C) 2011 Jamboree
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:seek Qi Seek Parser Directive ]
[heading Description]
The `seek[]` parser-directive skips all input until the subject parser matches.
[heading Header]
// forwards to <boost/spirit/repository/home/qi/directive/seek.hpp>
#include <boost/spirit/repository/include/qi_seek.hpp>
Also, see __include_structure__.
[heading Namespace]
[table
[[Name]]
[[`boost::spirit::repository::qi::seek`]]
]
[heading Model of]
[:__unary_parser_concept__]
[variablelist Notation
[[`a`] [A __parser_concept__.]]
]
[heading Expression Semantics]
Semantics of an expression is defined only where it differs from, or is
not defined in __unary_parser_concept__.
[table
[[Expression] [Semantics]]
[[`seek[a]`] [Advances until the parser `a` matches.]]
]
[heading Attributes]
See __qi_comp_attr_notation__.
[table
[[Expression] [Attribute]]
[[`seek[a]`]
[``a: A --> seek[a]: A
a: Unused --> seek[a]: Unused``]]
]
[heading Complexity]
[:The overall complexity is defined by the complexity of its subject
parser. The complexity of `seek` itself is O(N), where N is the number
of unsuccessful matches.]
[note *seeking sequence with skipping*
Using `seek[a >> b]` with skipping is inefficient, because when sequence fails, the backtracked position is non-skipped.
The solution is to ensure the input will always be pre-skipped, for example:
``
seek[lexeme[skip[a >> b]]]
``
does the trick.]
[heading Example]
[import ../../example/qi/seek.cpp]
The following example shows a simple use case of the `seek[]` directive, parsing C-style comment.
(For the full source of the example, see [@../../example/qi/seek.cpp seek.cpp])
Some namespace aliases:
[reference_qi_seek_namespace]
The input string and its iterators:
[reference_qi_seek_vars]
Parsing and showing the result:
[reference_qi_seek_parse]
[endsect]
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