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| <td width="21"> <h1></h1></td> |
| <td width="885"> <font face="Verdana, Arial, Helvetica, sans-serif"><b><font size="6">The |
| Input Policy</font></b></font></td> |
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| <blockquote> |
| <p><a href="class_reference_inptpolcy.html#introduction">Introduction</a><br> |
| <a href="class_reference_inptpolcy.html#header_synopsis">Header 'wave/cpp_iteration_context.hpp' |
| synopsis</a><br> |
| <a href="class_reference_inptpolcy.html#template_parameters">Template parameters</a><br> |
| <a href="class_reference_inptpolcy.html#member_functions">Member functions</a></p> |
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| <h2><b><a name="introduction"></a>Introduction</b></h2> |
| <p>The input policy type may be specified as a template parameter to the <tt>wave::context</tt> |
| object and is used for customizing the way, how an included file is to be represented |
| by a pair of iterators pointing to the beginning and the end of the resulting |
| input sequence. If this template parameter is not given while instantiating |
| the context object, it defaults to the <tt>iteration_context_policies::load_file_to_string</tt> |
| type. </p> |
| <h2><b><a name="header_synopsis"></a>Header <a href="http://svn.boost.org/trac/boost/browser/trunk/boost/wave/util/iteration_context.hpp">wave/iteration_context.hpp</a> |
| synopsis</b></h2> |
| <p>The following code listing does not show the required interface only, but for |
| brevity reasons the whole implementation of an input policy, which loads the |
| given file into a string variable and exposes the begin() and end() iterators |
| of this string to the <tt>Wave</tt> library.</p> |
| <pre><span class="keyword">namespace</span> boost { |
| <span class="keyword">namespace</span> wave { |
| <span class="keyword">namespace</span> iteration_context_policies { |
| |
| <span class="keyword">struct</span> load_file_to_string { |
| |
| <span class="keyword">template</span> <<span class="keyword">typename</span> IterContext> |
| <span class="keyword">class</span> inner { |
| |
| <span class="keyword">public</span>: |
| <span class="comment">// expose the begin and end iterators for the</span> |
| <span class="comment">// included file</span> |
| <span class="keyword">template</span> <typename Position> |
| <span class="keyword">static</span> |
| <span class="keyword">void</span> <a href="class_reference_inptpolcy.html#init_iterators">init_iterators</a>(IterContext&iter_ctx, |
| Position const &act_pos) |
| { |
| <span class="keyword">typedef typename</span> IterContext::iterator_type iterator_type; |
| |
| <span class="keyword">std::ifstream</span> instream(iter_ctx.filename.c_str()); |
| if (!instream.is_open()) { |
| CPP_THROW(preprocess_exception, bad_include_file, |
| iter_ctx.filename, act_pos); |
| } |
| |
| iter_ctx.instring = <span class="keyword">std::string</span>( |
| <span class="keyword">std::istreambuf_iterator</span><char>(instream.rdbuf()), |
| <span class="keyword">std::istreambuf_iterator</span><char>()); |
| |
| iter_ctx.first = iterator_type(iter_ctx.instring.begin(), |
| iter_ctx.instring.end(), |
| PositionT(iter_ctx.filename)); |
| iter_ctx.last = iterator_type(); |
| } |
| |
| <span class="keyword">private</span>: |
| <span class="keyword">std::string</span> instring; |
| }; |
| }; |
| |
| } <span class="comment">// namespace iteration_context_policies</span> |
| } <span class="comment">// namespace wave </span> |
| } <span class="comment">// namespace boost </span> </pre> |
| <p>As you can see, an <tt>input_policy</tt> for the <tt>wave::context</tt> object |
| should implement one function only, the init_iterators function. The policy |
| shown is implemented with the help of an embedded class to avoid the need for |
| template template parameters, which aren't implemented by all systems today. |
| This embedded class should have the name <tt>inner</tt>.</p> |
| <h3><a name="template_parameters"></a>Template Parameters</h3> |
| <p>The <tt>inner</tt> class is instantiated with one template parameter, the iteration |
| context type, from which the policy is a part of. The iterator type <tt>iterator_type</tt> |
| which is used to access the underlying input stream has to be derived through |
| a typedef as shown. The iterator pair to initialize (which is accessible as |
| <tt>iter_ctx.first</tt> and <tt>iter_ctx.last</tt>) has to initialized from |
| an abritrary iterator type, representing the actual input stream.</p> |
| <h3><a name="member_functions"></a>Member Functions</h3> |
| <p><a name="init_iterators"></a><b>init_iterators</b></p> |
| <pre> <span class="keyword">template</span> <<span class="keyword">typename</span> Position> |
| <span class="keyword">static void</span> init_iterators( |
| IterContext iter_ctx, |
| Position const &act_pos);</pre> |
| |
| <p>directive was found in the input token stream. The main rationale for this |
| function is to initialize the pair of iterators <tt>iter_ctx.first</tt> and |
| <tt>iter_ctx.last</tt>, which are to be used to access the input stream corresponding |
| to the include file to be inserted from inside the preprocessing engine.</p> |
| </blockquote> |
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| <p class="copyright">Copyright © 2003-2010 Hartmut Kaiser<br> |
| <br> |
| <font size="2">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) </font> </p> |
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| <p class="copyright"><span class="updated">Last updated: |
| <!-- #BeginDate format:fcAm1m -->Sunday, October 12, 2008 20:14<!-- #EndDate --> |
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