70 lines
2.5 KiB
Plaintext
70 lines
2.5 KiB
Plaintext
[/==============================================================================
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Copyright (C) 2001-2011 Joel de Guzman
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Copyright (C) 2001-2011 Hartmut Kaiser
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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 Sum - adding numbers]
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Here's a parser that sums a comma-separated list of numbers.
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[import ../../example/qi/sum.cpp]
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Ok we've glossed over some details in our previous examples. First, our
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includes:
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[tutorial_adder_includes]
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Then some using directives:
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[tutorial_adder_using]
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[table
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[[Namespace] [Description]]
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[[boost::phoenix] [All of phoenix]]
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[[boost::spirit] [All of spirit]]
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[[boost::spirit::qi] [All of spirit.qi]]
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[[boost::spirit::ascii] [ASCII version of `char_` and all char related parsers. Other
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encodings are also provided (e.g. also an ISO8859.1)]]
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[[boost::spirit::arg_names] [Special phoenix placeholders for spirit]]
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]
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[note If you feel uneasy with using whole namespaces, feel free to qualify your
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code, use namespace aliases, etc. For the purpose of this tutorial, we will be
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presenting unqualified names for both Spirit and __phoenix__. No worries, we
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will always present the full working code, so you won't get lost. In fact, all
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examples in this tutorial have a corresponding cpp file that QuickBook (the
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documentation tool we are using) imports in here as code snippets.]
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Now the actual parser:
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[tutorial_adder]
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The full cpp file for this example can be found here: [@../../example/qi/sum.cpp]
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This is almost like our original numbers list example. We're incrementally
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building on top of our examples. This time though, like in the complex number
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example, we'll be adding the smarts. There's an accumulator (`double& n`) that
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adds the numbers parsed. On a successful parse, this number is the sum of all
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the parsed numbers.
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The first `double_` parser attaches this action:
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ref(n) = _1
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This assigns the parsed result (actually, the attribute of `double_`) to `n`.
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`ref(n)` tells __phoenix__ that `n` is a mutable reference. `_1` is a
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__phoenix__ placeholder for the parsed result attribute.
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The second `double_` parser attaches this action:
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ref(n) += _1
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So, subsequent numbers add into `n`.
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That wasn't too bad, was it :-) ?
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[endsect]
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