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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> | |
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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 | |
44 | implemented. 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 | |
64 | preprocessing, 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> |