<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>The Context Object</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" href="theme/style.css" type="text/css">
</head>
<body text="#000000" background="theme/bkd.gif">
<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
Context Object</font></b></font></td>
<td width="96"><a href="http://spirit.sf.net"><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="quickstart.html"><img src="theme/l_arr.gif" width="20" height="19" border="0"></a></td>
<td width="20"><a href="class_reference_inputpolicy.html"><img src="theme/r_arr.gif" border="0"></a></td>
</tr>
</table>
<blockquote>
<p><a href="class_reference_context.html#introduction">Introduction</a><br>
<a href="class_reference_context.html#header_synopsis">Header 'wave/context.hpp' synopsis</a><br>
<a href="class_reference_context.html#template_parameters">Template parameters</a><br>
<a href="class_reference_context.html#member_functions">Member functions</a></p>
</blockquote>
<h2><b><a name="introduction"></a>Introduction</b></h2>
<p>The <tt>wave::context<></tt> object is the main user visible object of
the <tt>Wave</tt> library. It exists to generate the pair of iterators, which
while iterated return the preprocessed tokens. Additionally it is to be used
to control other aspects of the preprocessing, such as </p>
<blockquote>
<p><STRONG><IMG id="IMG1" height="13" src="theme/bullet.gif" width="13"></STRONG> include
search pathes, which define, where to search for files to be included with
<tt>#include <...></tt> and <tt>#include "..."</tt> directives<br>
<STRONG><img src="theme/bullet.gif" width="13" height="13"> </STRONG>which
macros to predefine and which of the predefined macros to undefine<br>
<STRONG><img src="theme/bullet.gif" width="13" height="13"> </STRONG>several
other options as for instance to control, whether to enable several extensions
to the C++ Standard (as for instance variadics and placemarkers) or not.</p>
</blockquote>
<h2><b><a name="header_synopsis"></a>Header <a href="http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/spirit/spirit/wave/wave/cpp_context.hpp?rev=HEAD&content-type=text/vnd.viewcvs-markup">wave/context.hpp</a>
synopsis</b></h2>
<pre><span class="keyword">namespace</span> wave {
<span class="keyword">template</span> <
<span class="keyword">typename</span> IteratorT, <span class="keyword">typename</span> TokenT,
<span class="keyword">typename</span> InputPolicyT, <span class="keyword">typename</span> TracePolicyT
>
<span class="keyword">class</span> context : <span class="keyword">public</span> InputPolicyT
{
<span class="keyword">public</span>:
<span class="keyword">typedef</span> pp_iterator<context> iterator_t;
<span class="comment">// constructor</span>
<a href="class_reference_context.html#constructor">context</a>(IteratorT <span class="keyword">const</span> &first_,
IteratorT <span class="keyword">const</span> &last_,
<span class="keyword">char const</span> *fname = <span class="string">"<Unknown>"</span>,
TracePolicyT &trace = TracePolicyT())
<span class="comment">// iterator interface</span>
iterator_t <a href="class_reference_context.html#iterator_interface_begin">begin</a>() <span class="keyword">const</span>;
iterator_t <a href="class_reference_context.html#iterator_interface_end">end</a>() <span class="keyword">const</span>;
<span class="comment">// maintain include paths</span>
<span class="keyword">bool</span> <a href="class_reference_context.html#add_include_path">add_include_path</a>(<span class="keyword">char const</span> *path_);
<span class="keyword">bool</span> <a href="class_reference_context.html#add_sysinclude_path">add_sysinclude_path</a>(<span class="keyword">char const</span> *path_);
<span class="keyword">void</span> <a href="class_reference_context.html#set_sysinclude_delimiter">set_sysinclude_delimiter</a>();
size_t <a href="class_reference_context.html#get_iteration_depth">get_iteration_depth</a>() <span class="keyword">const</span>;
<span class="comment">// maintain defined macros</span>
<span class="keyword">bool</span> <a href="class_reference_context.html#add_macro_definition">add_macro_definition</a>(<span class="keyword">std::string</span> macrostring,
<span class="keyword">bool</span> is_predefined = <span class="keyword">false</span>);
<span class="keyword">bool</span> <a href="class_reference_context.html#is_defined_macro">is_defined_macro</a>(<span class="keyword">std::string const</span> &name) <span class="keyword">const</span>;
<span class="keyword">bool</span> <a href="class_reference_context.html#remove_macro_definition">remove_macro_definition</a>(<span class="keyword">std::string const</span> &name,
<span class="keyword">bool</span> even_predefined = <span class="keyword">false</span>);
<span class="keyword">void</span> <a href="class_reference_context.html#reset_macro_definitions">reset_macro_definitions</a>();
<span class="comment">// other options</span>
<span class="keyword">void</span> <a href="class_reference_context.html#language_support">set_language</a>(wave::language_support enable);
wave::language_support <a href="class_reference_context.html#language_support">get_language</a>() <span class="keyword">const</span>;<br>
<span class="keyword">void</span> <a href="class_reference_context.html#set_max_include_nesting_depth">set_max_include_nesting_depth</a>(size_t new_depth);<br> size_t <a href="class_reference_context.html#set_max_include_nesting_depth">get_max_include_nesting_depth</a>() <span class="keyword">const</span>;<br>
<span class="comment">// get the Wave version information </span>
<span class="keyword">static std::string</span> <a href="class_reference_context.html#get_version">get_version</a>();
<span class="keyword">static std::string</span> <a href="class_reference_context.html#get_version">get_version_string</a>();
};
} <span class="comment">// namespace wave</span>
</pre>
<h2><b><a name="template_parameters"></a>Template parameters</b></h2>
<p>The <tt>wave::context</tt> object has three template parameters to specify
the concrete behaviour of its operation. The following table describes these
with more detail.</p>
<table width="90%" border="0" align="center">
<tr>
<td colspan="2" class="table_title"><b>Template parameters required for the
<tt>wave::context</tt> object</b></td>
</tr>
<tr>
<td width="32%" class="table_cells"><code>IteratorT</code></td>
<td width="68%" class="table_cells"><p>The type of the underlying iterator,
through which the input stream is accessed. <br>
This should be at least an <tt>forward_iterator</tt> type iterator.</p></td>
</tr>
<tr>
<td class="table_cells"><code>TokenT</code></td>
<td class="table_cells"><p>The type of the token to be used by the <tt>Wave</tt>
library and to be returned when dereferencing the iterator, returned from
the <tt>context</tt> object.</p></td>
</tr>
<tr>
<td class="table_cells"><code>InputPolicyT</code></td>
<td class="table_cells"><p>The type of the input policy class, which allows
to customize the behaviour of the Wave library and the type of the iterators
to use, when it comes to including and opening an included file.</p></td>
</tr>
<tr>
<td class="table_cells"><code>TracePolicyT</code></td>
<td class="table_cells"><p>The type of the trace policy class, which allows
to customize the trace output generated while expanding macros. </p></td>
</tr>
</table>
<p>For further information about the token type to use, please refer to the <a href="class_reference_tokentype.html">The
Token Type</a>.</p>
<p>If the template parameter <tt>InputPolicyT</tt> is omitted, the template <tt>wave::iteration_context_policies::load_file_to_string</tt>
is used. For further information about the input policy, please refer to the
topic <a href="class_reference_inputpolicy.html">The Input Policy</a>.</p>
<p>If the template parameter TracePolicyT is omitted, the <tt>wave::macro_trace_policies::no_tracing</tt>
policy type is used, i.e. by default there is no tracing performed. For further
information about the tracing policy, please refer to the topic <a href="class_reference_tracepolicy.html">The
Tracing Policy</a>. </p>
<h2><b><a name="member_functions"></a>Member functions</b></h2>
<p><b><a name="constructor" id="constructor"></a>Constructor</b></p>
<pre> context(IteratorT <span class="keyword">const</span> &first,
IteratorT <span class="keyword">const</span> &last,
<span class="keyword">char const</span> *filename,
TracePolicyT &trace);</pre>
<blockquote>
<p>Constructs a context object on top of the input stream given by the pair
of auxilliary iterators <tt>[first, last)</tt>. The iterators should
be at least <tt>forward_iterator</tt> type iterators. The filename parameter
is to be supplied for informational purposes only. This string is used for
indicating the token positions inside the input stream, it is not validated
against the file system. If the filename parameter is not given it defaults
to <span class="copyright">"<Unknown>"</span>. If the trace
parameter isn't supplied it defaults to a default constructed <tt>TracePolicyT</tt>
object. </p>
<p>Additionally the macro symbol table is filled with the predefined macros
and the current reference directory is set to the path of the given filename.
If this filename does not reference valid file system item, the current reference
directory is set to the current system directory. (The current reference directory
is the file system path, which is used as the target directory during the
processing of <tt>#include "..."</tt> directives),</p>
</blockquote>
<h3>Iterator interface</h3>
<p>The pair of iterators returned by the <tt>context::begin</tt> and <tt>context::end</tt>
functions is the main interface for accessing the preprocessed tokens from the
preprocessor engine. While iterating over the given iterator range <tt>[begin, end)</tt>
there are returned the preprocessed C++ tokens, which are generated on the fly
from the underlying input stream. The returned iterators are conceptually of
<tt>forward_iterator</tt> type.</p>
<p><b><a name="iterator_interface_begin"></a></b><b>begin</b></p>
<pre> iterator_t begin();</pre>
<blockquote>
<p>Initializes and returns the starting iterator for the preprocessed token
stream.</p>
</blockquote>
<p><b><a name="iterator_interface_end" id="iterator_interface_end"></a></b><b>end</b></p>
<pre> iterator_t end() <span class="keyword">const</span>;</pre>
<blockquote>
<p>Initializes and returns the end of stream iterator to compare with for detecting
the end of the preprocessed token stream.</p>
</blockquote>
<h3>Maintain include paths</h3>
<p>The <tt>Wave</tt> library maintains two separate search pathes for include
files. A search path for user include files and a search path for system include
files. Any directories specified with the <a href="#add_include_path">add_include_path()</a>
function before the function <a href="class_reference_context.html#set_sysinclude_delimiter">set_sysinclude_delimiter()</a>
is called are searched only for the case of <tt>#include "..."</tt>
directives, they are not searched for <tt>#include <file></tt> directives.
I.e. these directories are added to the user include search path. </p>
<p>If additional directories are specified with the <a href="#add_include_path">add_include_path()</a>
function after a call to the function <a href="class_reference_context.html#set_sysinclude_delimiter">set_sysinclude_delimiter()</a>,
these directories are searched for all <tt>#include</tt> directives. I.e. these
directories are added to the system include search path.</p>
<p>In addition, a call to the function <a href="class_reference_context.html#set_sysinclude_delimiter">set_sysinclude_delimiter()</a>
inhibits the use of the current reference directory as the first search directory
for <tt>#include "..."</tt> directives. Therefore, the current
reference directory is searched only, if it is requested explicitly with a call
to the function <a href="#add_include_path">add_include_path(".")</a>.
</p>
<p>Callig both functions, the <a href="class_reference_context.html#set_sysinclude_delimiter">set_sysinclude_delimiter()</a>
and <a href="#add_include_path">add_include_path(".")</a> allows you
to control precisely, which directories are searched before the current one
and which are searched after.</p>
<p>These functions are modelled after the command line behaviour implemented by
the popular gcc compiler.<br>
</p>
<p><a name="add_include_path"></a><b>add_include_path</b></p>
<pre> <span class="keyword">bool</span> add_include_path(<span class="keyword">char const</span> *path);
</pre>
<blockquote>
<p>Adds the given file system path to the user include search paths. After a
call to the <a href="#set_sys_include_delimiter">set_sysinclude_delimiter()</a>
this function adds the given file system path to the system include search
paths. Note though, that the given path is validated against the file system.
</p>
<p>If the given path string does not form a name of a valid file system directory
item, the function returns <tt>false</tt>. If the given path was successfully
added to the include search paths in question, the function returns <tt>true</tt>.</p>
</blockquote>
<p><a name="add_sysinclude_path"></a><b>add_sysinclude_path</b></p>
<pre> <span class="keyword">bool</span> add_sysinclude_path(<span class="keyword">char const</span> *path);</pre>
<blockquote>
<p>Adds the given file system path to the system include search paths. This
function operates on the system include search path regardless of the mode
of operation of the <a href="#add_include_path">add_include_path()</a>. Note
though, that the given path is validated against the file system.</p>
<p>If the given path string does not form a name of a valid file system directory
item, the function returns <tt>false</tt>. If the given path was successfully
added to the system include search paths, the function returns <tt>true</tt>.</p>
</blockquote>
<p><a name="set_sysinclude_delimiter" id="set_sysinclude_delimiter"></a><b>set_sysinclude_delimiter</b></p>
<pre> <span class="keyword">void</span> set_sysinclude_delimiter();</pre>
<blockquote>
<p>Switches the mode, how the <a href="#add_include_path">add_include_path()</a>
function operates. By default the given file system path is added to the user
include search paths. After calling this function a subsequent call to the
<a href="#add_include_path">add_include_path()</a> adds the given file system
path to the system include search paths. Additionally it inhibits the the
use of the current reference directory as the first search directory for <tt>#include "..."</tt>
directives.</p>
</blockquote>
<p><a name="get_iteration_depth"></a><b>get_iteration_depth</b></p>
<pre> size_t get_iteration_depth() <span class="keyword">const</span>;</pre>
<blockquote>
<p>Returns the actual include iteration depth, i.e. the current number of include
levels to be poped from the include iteration context, before the main (topmost)
iteration context is reached.</p>
</blockquote>
<h3>Maintain defined macros</h3>
<p><a name="add_macro_definition"></a><b>add_macro_definition</b></p>
<pre><span class="keyword"> bool</span> add_macro_definition(
<span class="keyword">std::string</span> macrostring,
bool is_predefined);
</pre>
<blockquote>
<p>Adds a new macro definition to the macro symbol table. The parameter <tt>macrostring</tt>
should contain the macro to define in the command line format, i.e. something
like <tt>MACRO(x)=definition</tt>. The following table describes this format
in more detail. The parameter <tt>is_predefined</tt> should be true while
defining predefined macros, i.e. macros, which are not undefinable with an
<tt>#undef</tt> directive from inside the preprocessed input stream. If this
parameter is not given, it defaults to <tt>false</tt>.</p>
<table width="90%" border="0" align="center">
<tr>
<td colspan="2" class="table_title"><b>Summary of possible formats for defining
macros </b></td>
</tr>
<tr>
<td width="32%" class="table_cells"><code>MACRO</code></td>
<td width="68%" class="table_cells"><code>define <tt>MACRO</tt> as 1</code></td>
</tr>
<tr>
<td class="table_cells"><code>MACRO=</code></td>
<td class="table_cells"><code>define <tt>MACRO</tt> as nothing (empty)</code></td>
</tr>
<tr>
<td class="table_cells"><code>MACRO=definition</code></td>
<td class="table_cells"><code>define <tt>MACRO</tt> as <tt>definition</tt></code></td>
</tr>
<tr>
<td width="32%" class="table_cells"><code>MACRO(x)</code></td>
<td width="68%" class="table_cells"><code>define <tt>MACRO(x)</tt> as 1</code></td>
</tr>
<tr>
<td class="table_cells"><code>MACRO(x)=</code></td>
<td class="table_cells"><code>define <tt>MACRO(x)</tt> as nothing (empty)</code></td>
</tr>
<tr>
<td class="table_cells"><code>MACRO(x)=definition</code></td>
<td class="table_cells"><code>define <tt>MACRO(x)</tt> as <tt>definition</tt></code></td>
</tr>
</table>
<p>The function returns <tt>false</tt>, if the macro to define already was defined
and the new definition is equivalent to the existing one, it returns true,
if the new macro was successfully added to the macro symbol table.</p>
<p>If the given macro definition resembles a redefinition and the new macro
is not identical to the already defined macro (in the sense defined by the
C++ Standard), the function throws a corresponding <tt>preprocess_exception</tt>.</p>
</blockquote>
<p><a name="is_defined_macro"></a><b>is_defined_macro</b></p>
<pre><span class="keyword"> bool</span> is_defined_macro(<span class="keyword">std::string const</span> &name) <span class="keyword">const</span>; </pre>
<blockquote>
<p>Returns, if a macro with the given <tt>name</tt> is defined, i.e. if it is
contained in the macro symbol table.</p>
</blockquote>
<p><a name="remove_macro_definition"></a><b>remove_macro_definition</b></p>
<pre><span class="keyword"> bool</span> remove_macro_definition(
<span class="keyword">std::string const</span> &name,
<span class="keyword">bool</span> even_predefined); </pre>
<blockquote>
<p>Removes the definition of the macro with the given <tt>name</tt> from the
macro symbol table. This operation is equivalent to an <tt>#undef</tt> directive
with this <tt>name</tt> executed from within the input stream. If the parameter
<tt>even_predefined</tt> is <tt>true</tt>, then the macro is removed from
the macro symbol table even, if it is defined as a predefined macro. </p>
<p>Note though, that the following macros are <b>not</b> undefinable in any
case: <tt>__FILE__</tt>, <tt>__LINE__</tt>, <tt>__DATE__</tt>, <tt>__TIME__</tt>,
<tt>__cplusplus</tt>, <tt>__STDC__</tt>. If the parameter <tt>even_predefined</tt>
is not given, it defaults to <tt>false</tt>.</p>
<p>The function returns <tt>false</tt>, if the macro to undefine was not defined
and returns <tt>true</tt> otherwise.</p>
<p>If the macro to remove may not be undefined (it is a predefined macro and
the parameter <tt>even_predefined</tt> is set to <tt>false</tt> or it is one
of the mentioned not undefinable macros above) the function throws a <tt>preprocess_exception</tt>.</p>
</blockquote>
<p><a name="reset_macro_definitions"></a><b>reset_macro_definitions</b></p>
<pre><span class="keyword"> void</span> reset_macro_definitions(); </pre>
<blockquote>
<p>Resets the macro symbol table to it's initial state, i.e. undefines all user
defined macros and inserts the internal predefined macros as described <a href="predefined_macros.html">here</a>.</p>
</blockquote>
<h3><a name="get_version"></a>Get Version information</h3>
<p><b>get_version</b></p>
<pre><span class="keyword"> </span><span class="keyword">static std::string</span> get_version(); </pre>
<blockquote>
<p>Returns a string containing the current Wave version formatted as <span class="string">0xvvrsbbbb</span>
(this is a string representation of the equivalent hexadecimal number), where
<span class="literal">'vv'</span> is the version number, <span class="literal">'r'</span>
the release number, <span class="literal">'s'</span> the subrelease number
and <span class="literal">'bbbb'</span> the build number. A possible return
value looks like <span class="literal">0x00910454</span>. The returned value
is the same as is inserted in the preprocessed token stream, when the predefined
macro <tt>__WAVE_VERSION__</tt> is expanded.</p>
</blockquote>
<p><b>get_version_str</b></p>
<pre><span class="keyword"> </span><span class="keyword">static std::string</span> get_version_str(); </pre>
<blockquote>
<p>Returns a string containing the current Wave version formatted as <span class="string">"v.rr.ss.bbbb"</span>,
where <span class="literal">'v'</span> is the version number, <span class="literal">'rr'</span>
the release number, <span class="literal">'ss'</span> the subrelease number
and <span class="literal">'bbbb'</span> the build number. A possible return
value looks like <span class="literal">"0.9.1.454"</span>. The returned
value is the same as is inserted in the preprocessed token stream, when the
predefined macro <tt>__WAVE_VERSION_STR__</tt> is expanded.</p>
</blockquote>
<h3>Control extended options</h3>
<p><a name="support_variadics_and_placemarkers"></a>set_language<br>
get_language</p>
<pre><span class="keyword"> void</span> set_language(<span class="keyword">wave::language_support</span> language);
<span class="keyword">wave::language_support</span> get_language() <span class="keyword">const</span>;</pre>
<blockquote>
<p>This functions allow to specify the language mode, in which the <tt>Wave</tt>
library should work. The possible language modes are defined by the enumerated
type <tt>wave::language_support</tt>:</p>
<pre> <span class="keyword">enum</span> language_support {
<span class="comment">// support flags for C++98</span>
support_normal = 0x01,
support_cpp = support_normal,
<span class="comment">// support flags for C99</span>
support_variadics = 0x02,
support_c99 = support_variadics,
<span class="comment">// support flags for experimental C++0x features</span>
support_extensions = 0x04,
support_cpp0x = support_normal |
support_variadics |
support_extensions,
};</pre>
<p>When used with <tt>support_variadics</tt> the support for variadics, placemarkers
and the <tt>operator _Pragma()</tt> is enabled in normal C++ mode. The <tt>support_c99</tt>
and <tt>support_cpp0x</tt> switch to the respective language support.</p>
</blockquote>
<p><a name="set_max_include_nesting_depth" id="set_max_include_nesting_depth"></a>set_max_include_nesting_depth<br>
g et_max_include_nesting_depth</p>
<pre><span class="keyword"> void</span> set_max_include_nesting_depth(size_t new_depth);
size_t get_max_include_nesting_depth() <span class="keyword">const</span>;</pre>
<blockquote>
<p>This functions allow to set or to get the maximal possible include file nesting
depth supported by the <tt>Wave</tt> library. The initial value for this is
determined by the preprocessing constant <tt>WAVE_MAX_INCLUDE_LEVEL_DEPTH</tt>
(see <a href="compiletime_config.html">here</a>).</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="quickstart.html"><img src="theme/l_arr.gif" width="20" height="19" border="0"></a></td>
<td width="20"><a href="class_reference_inputpolicy.html"><img src="theme/r_arr.gif" border="0"></a></td>
</tr>
</table>
<hr size="1">
<p class="copyright">Copyright © 2003 Hartmut Kaiser<br>
<br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
is granted provided this copyright notice appears in all copies. This document
is provided "as is" without express or implied warranty, and with
no claim as to its suitability for any purpose. </font></p>
<span class="updated">Last updated:
<!-- #BeginDate format:fcAm1m -->Saturday, May 10, 2003 21:43<!-- #EndDate -->
</span>
<p> </p>
</body>
</html>
Submit an article or tip