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      <h1></h1>
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    <td width="885"> <font face="Verdana, Arial, Helvetica, sans-serif"><b><font size="6">Preface</font></b></font></td>

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<p>During the last time many new features have been developed as additions to the <tt>Spirit</tt> 
  <a href="references.html#spirit">[4]</a> parser construction framework and we 
  felt more and more, that it would be very helpful, to have a 'real world' example, 
  which could be used as a sandbox for testing the usability of certain features. 
  Additionally&nbsp;a recent discussion on the Boost mailing list showed the widespread 
  interest of developers to have a modern, open source C++ preprocessor library 
  to play with.&nbsp; So we had the idea to implement a C++ preprocessor to fit 
  this needs&nbsp;-&nbsp;<tt>Wave</tt> was born.</p>

<p align="justify">The <tt>Wave</tt> C++ preprocessor library uses the <a href="http://www.boost.org/"> 
  </a> <tt>Spirit<a href="references.html#spirit">[4]</a></tt> parser construction 
  library to implement a C++ lexer with ISO/ANSI Standards conformant preprocessing 
  capabilities. It exposes an iterator interface, which returns the current preprocessed 
  token from the input stream. This preprocessed token is generated on the fly 
  while iterating over the preprocessor iterator sequence (in the terminology 
  of the STL these iterators are forward iterators). </p>

<p align="justify"> The C++ preprocessor is a macro processor that under normal 
  circumstances is used automatically by your C++ compiler to transform your program 
  before actual compilation. It is called a macro processor because it allows 
   to define macros, which are brief abbreviations for longer constructs. The 
  C++ preprocessor provides four separate facilities that you can use as you see 
  fit: </p>

<blockquote> 
  
  <p><b><img src="theme/bullet.gif" id="IMG1" height="13" width="13">&nbsp;</b>Inclusion 
    of header files<br>

    <b><img src="theme/bullet.gif" id="IMG2" height="13" width="13">&nbsp;</b>Macro 
    expansion<br>

    <b><img src="theme/bullet.gif" id="IMG3" height="13" width="13">&nbsp;</b>Conditional 
    compilation<br>

    <b><img src="theme/bullet.gif" id="IMG4" height="13" width="13">&nbsp;</b>Line 
    control</p>

</blockquote>

<p>These features are greatly underestimated today, even more, the preprocessor 
  has been frowned on for so long that its usage just hasn't been effectively 
  pushed until the Boost preprocessor library <a href="references.html#pp_lib">[7]</a> 
  came into being a few years ago. Only today we begin to understand, that preprocessor 
  generative metaprogramming combined with template metaprogramming in C++ is 
  by far one of the most powerful compile-time reflection/metaprogramming facilities 
  that any language has ever supported.</p>

<p>The C++ Standard <a href="http://webstore.ansi.org/ansidocstore/product.asp?sku=INCITS%2FISO%2FIEC%2B14882%2D1998">[2] </a>
was adopted back in 1998, but there is still no (known to me)
commercial C++ compiler, which has a bugfree implementation of the
rather simple preprocessor requirements mandated therein. This may be a
result of the mentioned underestimation or even banning of the
preprocessor from good programming style during the last few years or
may stem from the somewhat awkward standardese dialect of English used
to describe it. Two open source projects are exceptions of this: gcc
and Clang (a subproject of LLVM), both providing preprocessors with
very good standards conformance. </p>

<p align="justify">So the main goals for the <tt>Wave</tt> project are:</p>

<blockquote> 
  
  <p><b><img src="theme/bullet.gif" id="IMG5" height="13" width="13">&nbsp;</b>full 
    conformance with the C++ standard (ISO/IEC 14882:1998) <a href="references.html#iso_cpp">[1]</a> 
    and with the C99 standard (INCITS/ISO/IEC 9899:1999) <a href="references.html#iso_c">[2]</a><br>

    <b><img src="theme/bullet.gif" height="13" width="13">&nbsp;</b>usage of <tt>Spirit<a href="references.html#spirit">[4]</a></tt> 
    for the parsing parts of the game (certainly :-)<br>

    <b><img src="theme/bullet.gif" height="13" width="13">&nbsp;</b>maximal usage 
    of STL and/or <tt>Boost</tt> libraries (for compactness and maintainability)<br>

    <b><img src="theme/bullet.gif" height="13" width="13">&nbsp;</b>straightforward 
    extendability for the implementation of additional features<br>

    <b><img src="theme/bullet.gif" height="13" width="13">&nbsp;</b>building a 
    flexible library for different C++ lexing and preprocessing needs</p>

</blockquote>

<p>At the first steps it is not planned to make a very high performance
or very small C++ preprocessor. If you are looking for these objectives
you probably have to look at other places. Although our C++
preprocessor iterator works as expected and is usable as a reference
implementation, for instance for testing of other preprocessor oriented
libraries as the Boost Preprocessor library <a href="references.html#pp_lib">[7]</a> et.al. Nevertheless recent work has lead to surprising performance enhancements (if compared
  with earlier versions). Wave is still somewhat slower as for instance EDG
  based preprocessors (Intel, Comeau) on simple input files, however, as
  complexity increases, time dilates expontentially on EDG. Preprocessing time
  dilates linearly under Wave, which causes it to easily outperform EDG based
preprocessors when complexity increases.</p>

<p>As tests showed, the <tt>Wave</tt> library is very conformant to the C++ Standard, 
  such that it compiles several strict conformant macro definitions, which are 
not even compilable with EDG based preprocessors (i.e. Comeau or Intel). </p>

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<p class="copyright">Copyright &copy; 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>

<span class="updated"></span>
<p class="copyright"><span class="updated">Last updated: 
  <!-- #BeginDate format:fcAm1m -->Sunday, December 2, 2007  19:03<!-- #EndDate -->
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