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<td width="885"> <font face="Verdana, Arial, Helvetica, sans-serif"><b><font size="6">Introduction</font></b></font></td>
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<P dir="ltr">The <tt>Wave</tt> C++ preprocessor library is a Standards conformant
implementation of the mandated C++ preprocessor functionality packed behind
a simple to use interface, which integrates well with the well known idioms
of the Standard Template Library (STL).</P>
<P dir="ltr">The <tt>Wave</tt> C++ preprocessor is not a monolitic application,
it's rather a modular library, which exposes mainly a context object and an
iterator interface. The context object helps to configure the actual preprocessing
process (as search path's, predefined macros, etc.). The exposed iterators are
generated by this context object too. Iterating over the sequence defined by
the two iterators will return the preprocessed tokens, which are to be built
on the fly from the given input stream. </P>
<P dir="ltr"> The C++ preprocessor iterator itself is feeded by a C++ lexer iterator,
which implements an unified interface. BTW, the C++ lexers contained with the
<tt>Wave</tt> library may be used standalone too and are not tied to the C++
preprocessor iterator at all. </P>
<P dir="ltr">To make the C++ preprocessing library modular, the C++ lexer is held
completely separate and independend from the preprocessor. To proof this concept,
there are two different C++ lexers implemented by now, which are functionally
completely identical. The C++ lexers expose the mentioned unified interface,
so that the C++ preprocessor iterator may be used with both of them. The abstraction
of the C++ lexer from the C++ preprocessor iterator library was done to allow
to plug in different C++ lexers without the need to reimplement the preprocessor.
This will allow for benchmarking and specific finetuning of the process of preprocessing
itself.</P>
<P dir="ltr">The first of this C++ lexers is implemented with the help of the
wellknown <tt>re2c</tt> <a href="references.html#re2c">[3]</a> tool, which generates
C code from given regular expressions. The lexers generated with <tt>re2c</tt>
are known to be very fast, because they are not table driven but the whole
token building logic is coded directly (very similar to hand coded lexers).
</P>
<P dir="ltr">The second of this C++ lexers is build around a table driven lexer,
where the DFA tables are generated from regular expressions with the help of
a Spirit based lexer generating framework named <tt>Slex</tt> <a href="references.html#slex">[5]</a>.
The <tt>Slex</tt> is feeded during runtime with the token definitions (regular
expressions) and generates the resulting DFA table. This table is used to combine
the input characters into corresponding lexems (tokens). The generated DFA table
can be saved to disc to avoid the generation process at program startup.</P>
<P dir="ltr">It is possible to build other C++ lexers if needed. Currently there
are plans to adapt the <tt>Spirit</tt> C++ lexer example <tt>cpplexer</tt> <a href="references.html#cpplexer">[6]</a>,
which is completely based on static <tt>Spirit<a href="references.html#spirit">[4]</a></tt>
grammars.</P>
<P dir="ltr">In fact both of the embedded lexers and the library itself is able
to act in a C99 compliant mode. In this mode the lexers reject C++ only tokens
(<tt>'::'</tt>, <tt>'->*'</tt>, <tt>'.*'</tt> and the alternate keywords
as <tt>'and'</tt> etc.). The preprocessor additionally handles placemarkers
(empty macro arguments) and variadics (macros with variable parameter count).
As an extension to the C++ Standard the library can be enabled to handle placemarkers
and variadics in the C++ mode too.</P>
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<p class="copyright">Copyright © 2003-2004 Hartmut Kaiser<br>
<br>
<font size="2">Use, modification and distribution is subject to 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">Last updated:
<!-- #BeginDate format:fcAm1m -->Monday, January 5, 2004 14:57<!-- #EndDate -->
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