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| <td width="21"> <h1></h1></td> |
| <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 C99/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 monolithic 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 built |
| on the fly from the given input stream. </P> |
| <P dir="ltr"> The C++ preprocessor iterator itself is fed by a C++ lexer iterator, |
| which implements an abstract interface. The C++ lexers packaged 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 independent from the preprocessor. To prove this concept, |
| two different, but functionally identical C++ lexers were |
| 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, |
| so that the C++ preprocessor iterator may be used with all of them. The abstraction |
| of the lexer from the preprocessor iterator library was done to allow |
| plugging in different lexers without the need to reimplement the preprocessor. |
| This will allow for benchmarking and specific fine tuning of the process of preprocessing |
| itself.</P> |
| <P dir="ltr">The first of these C++ lexers is implemented with the help of the |
| well known <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 directly code the token building logic |
| (very similar to hand coded lexers). |
| </P> |
| <P dir="ltr">The second of these C++ lexers is built around a table driven lexer, |
| where the DFA tables (discrete finite automaton 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 fed 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 lexemes (tokens). The generated DFA table |
| can be saved to disk to avoid the generation process at program startup.</P> |
| <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 |
| preprocessing, but allows to use Wave for all of the IDL derivatives. </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">Both of the included lexers and the library itself are 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 |
| such as <tt>'and'</tt>, etc.). The preprocessor additionally handles placemarkers |
| (empty macro arguments) and variadics (macros with variable parameter counts). |
| As an extension to the C++ Standard, the library can be enabled to handle placemarkers |
| and variadics in C++ mode too.</P> |
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| <p class="copyright">Copyright © 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> |
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| <p class="copyright"><span class="updated">Last updated: |
| <!-- #BeginDate format:fcAm1m -->Sunday, December 2, 2007 19:03<!-- #EndDate --> |
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