133 lines
7.0 KiB
HTML
133 lines
7.0 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
|
<html>
|
|
<head>
|
|
<title>The Input Policy</title>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
|
|
<link href="theme/style.css" rel="stylesheet" type="text/css">
|
|
</head>
|
|
|
|
<body>
|
|
<table width="100%" border="0" cellspacing="2" background="theme/bkd2.gif">
|
|
<tr>
|
|
<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>
|
|
<td width="96"><a href="http://www.boost.org"><img src="theme/wave.gif" width="93" height="68" align="right" border="0"></a></td>
|
|
</tr>
|
|
</table>
|
|
<br>
|
|
<table border="0">
|
|
<tr>
|
|
<td width="10"></td>
|
|
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
|
|
<td width="30"><a href="class_reference_context.html"><img src="theme/l_arr.gif" width="20" height="19" border="0"></a></td>
|
|
<td width="30"><a href="class_reference_ctxpolicy.html"><img src="theme/r_arr.gif" border="0"></a></td>
|
|
</tr>
|
|
</table>
|
|
|
|
<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>
|
|
<table border="0">
|
|
<tr>
|
|
<td width="10"></td>
|
|
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
|
|
<td width="30"><a href="class_reference_context.html"><img src="theme/l_arr.gif" width="20" height="19" border="0"></a></td>
|
|
<td width="30"><a href="class_reference_ctxpolicy.html"><img src="theme/r_arr.gif" border="0"></a></td>
|
|
</tr>
|
|
</table>
|
|
<hr size="1">
|
|
<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 -->
|
|
</span></p>
|
|
</body>
|
|
</html>
|