184 lines
7.4 KiB
HTML
184 lines
7.4 KiB
HTML
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<title>Preface</title>
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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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<td width="96"><a href="http://www.boost.org"><img src="theme/wave.gif" align="right" border="0" height="68" width="93"></a></td>
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<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
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<td width="30"><img src="theme/l_arr_disabled.gif" border="0" height="19" width="20"></td>
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<td width="30"><a href="introduction.html"><img src="theme/r_arr.gif" border="0"></a></td>
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<p>During the last time many new features have been developed as additions to the <tt>Spirit</tt>
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<a href="references.html#spirit">[4]</a> parser construction framework and we
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felt more and more, that it would be very helpful, to have a 'real world' example,
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which could be used as a sandbox for testing the usability of certain features.
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Additionally a recent discussion on the Boost mailing list showed the widespread
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interest of developers to have a modern, open source C++ preprocessor library
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to play with. So we had the idea to implement a C++ preprocessor to fit
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this needs - <tt>Wave</tt> was born.</p>
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<p align="justify">The <tt>Wave</tt> C++ preprocessor library uses the <a href="http://www.boost.org/">
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</a> <tt>Spirit<a href="references.html#spirit">[4]</a></tt> parser construction
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library to implement a C++ lexer with ISO/ANSI Standards conformant preprocessing
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capabilities. It exposes an iterator interface, which returns the current preprocessed
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token from the input stream. This preprocessed token is generated on the fly
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while iterating over the preprocessor iterator sequence (in the terminology
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of the STL these iterators are forward iterators). </p>
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<p align="justify"> The C++ preprocessor is a macro processor that under normal
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circumstances is used automatically by your C++ compiler to transform your program
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before actual compilation. It is called a macro processor because it allows
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to define macros, which are brief abbreviations for longer constructs. The
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C++ preprocessor provides four separate facilities that you can use as you see
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fit: </p>
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<blockquote>
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<p><b><img src="theme/bullet.gif" id="IMG1" height="13" width="13"> </b>Inclusion
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of header files<br>
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<b><img src="theme/bullet.gif" id="IMG2" height="13" width="13"> </b>Macro
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expansion<br>
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<b><img src="theme/bullet.gif" id="IMG3" height="13" width="13"> </b>Conditional
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compilation<br>
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<b><img src="theme/bullet.gif" id="IMG4" height="13" width="13"> </b>Line
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control</p>
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</blockquote>
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<p>These features are greatly underestimated today, even more, the preprocessor
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has been frowned on for so long that its usage just hasn't been effectively
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pushed until the Boost preprocessor library <a href="references.html#pp_lib">[7]</a>
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came into being a few years ago. Only today we begin to understand, that preprocessor
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generative metaprogramming combined with template metaprogramming in C++ is
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by far one of the most powerful compile-time reflection/metaprogramming facilities
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that any language has ever supported.</p>
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<p>The C++ Standard <a href="http://webstore.ansi.org/ansidocstore/product.asp?sku=INCITS%2FISO%2FIEC%2B14882%2D1998">[2] </a>
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was adopted back in 1998, but there is still no (known to me)
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commercial C++ compiler, which has a bugfree implementation of the
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rather simple preprocessor requirements mandated therein. This may be a
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result of the mentioned underestimation or even banning of the
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preprocessor from good programming style during the last few years or
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may stem from the somewhat awkward standardese dialect of English used
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to describe it. Two open source projects are exceptions of this: gcc
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and Clang (a subproject of LLVM), both providing preprocessors with
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very good standards conformance. </p>
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<p align="justify">So the main goals for the <tt>Wave</tt> project are:</p>
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<blockquote>
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<p><b><img src="theme/bullet.gif" id="IMG5" height="13" width="13"> </b>full
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conformance with the C++ standard (ISO/IEC 14882:1998) <a href="references.html#iso_cpp">[1]</a>
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and with the C99 standard (INCITS/ISO/IEC 9899:1999) <a href="references.html#iso_c">[2]</a><br>
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<b><img src="theme/bullet.gif" height="13" width="13"> </b>usage of <tt>Spirit<a href="references.html#spirit">[4]</a></tt>
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for the parsing parts of the game (certainly :-)<br>
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<b><img src="theme/bullet.gif" height="13" width="13"> </b>maximal usage
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of STL and/or <tt>Boost</tt> libraries (for compactness and maintainability)<br>
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<b><img src="theme/bullet.gif" height="13" width="13"> </b>straightforward
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extendability for the implementation of additional features<br>
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<b><img src="theme/bullet.gif" height="13" width="13"> </b>building a
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flexible library for different C++ lexing and preprocessing needs</p>
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</blockquote>
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<p>At the first steps it is not planned to make a very high performance
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or very small C++ preprocessor. If you are looking for these objectives
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you probably have to look at other places. Although our C++
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preprocessor iterator works as expected and is usable as a reference
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implementation, for instance for testing of other preprocessor oriented
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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
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with earlier versions). Wave is still somewhat slower as for instance EDG
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based preprocessors (Intel, Comeau) on simple input files, however, as
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complexity increases, time dilates expontentially on EDG. Preprocessing time
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dilates linearly under Wave, which causes it to easily outperform EDG based
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preprocessors when complexity increases.</p>
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<p>As tests showed, the <tt>Wave</tt> library is very conformant to the C++ Standard,
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such that it compiles several strict conformant macro definitions, which are
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not even compilable with EDG based preprocessors (i.e. Comeau or Intel). </p>
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<table border="0">
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<tbody>
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<tr>
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<td width="10"></td>
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<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
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<td width="30"><img src="theme/l_arr_disabled.gif" border="0" height="19" width="20"></td>
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<td width="30"><a href="introduction.html"><img src="theme/r_arr.gif" border="0"></a></td>
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</tr>
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</tbody>
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</table>
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<hr size="1">
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<p class="copyright">Copyright © 2003-2011 Hartmut Kaiser<br>
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<br>
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<font size="2">Distributed under the Boost Software License, Version
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1.0. (See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt) </font> </p>
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<span class="updated"></span>
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<p class="copyright"><span class="updated">Last updated:
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<!-- #BeginDate format:fcAm1m -->Sunday, January 9, 2011 16:17<!-- #EndDate -->
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</span></p>
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