1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2<html> 3<head> 4<title>Introduction</title> 5<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> 6<link href="theme/style.css" rel="stylesheet" type="text/css"> 7</head> 8 9<body text="#000000" background="theme/bkd.gif"> 10<table width="100%" border="0" cellspacing="2" background="theme/bkd2.gif"> 11 <tr> 12 <td width="21"> <h1></h1></td> 13 <td width="885"> <font face="Verdana, Arial, Helvetica, sans-serif"><b><font size="6">Introduction</font></b></font></td> 14 <td width="96"><a href="http://www.boost.org"><img src="theme/wave.gif" width="93" height="68" align="right" border="0"></a></td> 15 </tr> 16</table> 17<br> 18<table border="0"> 19 <tr> 20 <td width="10"></td> 21 <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> 22 <td width="30"><a href="preface.html"><img src="theme/l_arr.gif" width="20" height="19" border="0"></a></td> 23 <td width="30"><a href="quickstart.html"><img src="theme/r_arr.gif" border="0"></a></td> 24 </tr> 25</table> 26<P dir="ltr">The <tt>Wave</tt> C++ preprocessor library is a Standards conformant 27 implementation of the mandated C99/C++ preprocessor functionality packed behind 28 a simple to use interface, which integrates well with the well known idioms 29 of the Standard Template Library (STL).</P> 30<P dir="ltr">The <tt>Wave</tt> C++ preprocessor is not a monolithic application, 31 it's rather a modular library, which exposes mainly a context object and an 32 iterator interface. The context object helps to configure the actual preprocessing 33 process (as search path's, predefined macros, etc.). The exposed iterators are 34 generated by this context object too. Iterating over the sequence defined by 35 the two iterators will return the preprocessed tokens, which are built 36 on the fly from the given input stream. </P> 37<P dir="ltr"> The C++ preprocessor iterator itself is fed by a C++ lexer iterator, 38 which implements an abstract interface. The C++ lexers packaged with the 39 <tt>Wave</tt> library may be used standalone, too, and are not tied to the C++ 40 preprocessor iterator at all. </P> 41<P dir="ltr">To make the C++ preprocessing library modular, the C++ lexer is held 42 completely separate and independent from the preprocessor. To prove this concept, 43 two different, but functionally identical C++ lexers were 44implemented. Additionally there is implemented a IDL lexer, which allows to use the preprocessor library as the lexing component of a IDL oriented tool. All these lexers implement the mentioned abstract interface, 45 so that the C++ preprocessor iterator may be used with all of them. The abstraction 46 of the lexer from the preprocessor iterator library was done to allow 47 plugging in different lexers without the need to reimplement the preprocessor. 48 This will allow for benchmarking and specific fine tuning of the process of preprocessing 49 itself.</P> 50<P dir="ltr">The first of these C++ lexers is implemented with the help of the 51 well known <tt>Re2C</tt> <a href="references.html#re2c">[3]</a> tool, which generates 52 C code from given regular expressions. The lexers generated with <tt>Re2C</tt> 53 are known to be very fast, because they are not table driven but directly code the token building logic 54(very similar to hand coded lexers). 55</P> 56<P dir="ltr">The second of these C++ lexers is built around a table driven lexer, 57 where the DFA tables (discrete finite automaton tables) are generated from regular expressions with the help of 58 a Spirit-based lexer generating framework named <tt>Slex</tt> <a href="references.html#slex">[5]</a>. 59 The <tt>Slex</tt> is fed during runtime with the token definitions (regular 60 expressions) and generates the resulting DFA table. This table is used to combine 61 the input characters into corresponding lexemes (tokens). The generated DFA table 62 can be saved to disk to avoid the generation process at program startup.</P> 63<P dir="ltr">Wave may be used for preprocessing IDL files too, since the token set needed for the IDL language is very similar to the C++ token set. That's the reason, why the <tt>Wave</tt> preprocessor library contains also an IDL lexer. The IDL lexer is also based on the <tt>Re2C</tt> tool, but recognizes a different set of tokens. So this lexer does not recognize any keywords (except <tt>true</tt> and <tt>false</tt>, which are needed by the preprocessor itself). This is needed because there exist different IDL language flavours, where identifiers of one flavour may be keywords of others - Ok, this requires postponement of keyword identification until after the 64preprocessing, but allows to use Wave for all of the IDL derivatives. </P> 65<P dir="ltr">It is possible to build other C++ lexers if needed. Currently there 66 are plans to adapt the <tt>Spirit</tt> C++ lexer example <tt>cpplexer</tt> <a href="references.html#cpplexer">[6]</a>, 67 which is completely based on static <tt>Spirit<a href="references.html#spirit">[4]</a></tt> 68 grammars.</P> 69<P dir="ltr">Both of the included lexers and the library itself are able 70 to act in a C99 compliant mode. In this mode the lexers reject C++-only tokens 71 (<tt>'::'</tt>, <tt>'->*'</tt>, <tt>'.*'</tt> and the alternate keywords 72 such as <tt>'and'</tt>, etc.). The preprocessor additionally handles placemarkers 73 (empty macro arguments) and variadics (macros with variable parameter counts). 74 As an extension to the C++ Standard, the library can be enabled to handle placemarkers 75 and variadics in C++ mode too.</P> 76<table border="0"> 77 <tr> 78 <td width="10"></td> 79 <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td> 80 <td width="30"><a href="preface.html"><img src="theme/l_arr.gif" width="20" height="19" border="0"></a></td> 81 <td width="30"><a href="quickstart.html"><img src="theme/r_arr.gif" border="0"></a></td> 82 </tr> 83</table> 84<hr size="1"> 85<p class="copyright">Copyright © 2003-2011 Hartmut Kaiser<br> 86 <br> 87<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> 88<span class="updated"></span> 89<p class="copyright"><span class="updated">Last updated: 90 <!-- #BeginDate format:fcAm1m -->Sunday, December 2, 2007 19:03<!-- #EndDate --> 91</span> </p> 92</body> 93</html> 94
