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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>
- </blockquote>
- <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><char>(instream.rdbuf()),
- <span class="keyword">std::istreambuf_iterator</span><char><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 © 2003-2011 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>
- <span class="updated"></span>
- <p class="copyright"><span class="updated">Last updated:
- <!-- #BeginDate format:fcAm1m -->Sunday, October 12, 2008 20:14<!-- #EndDate -->
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