Flex++ Bisonc++ parser

Question

I'm trying to use flex and bison in my project to generate a parser code for a file structure. Main programming language is C++ and project is on an OO design mainly running in parallel.

I heard that flex and bison generated parsers are C codes and they're not reenterant. Googling, I found flex++ and bisonc++. Unfortunately there is no simple tutorial to get started. Most examples are based on bison/flex. Some people somehow integrated bison/flex parsers in their C++ code. They supposed to be "tricky"...

Documentation of flex++ and bisonc++ doesn't help me and. Tutorials and examples, they all get input from stdin and print some messages on stdout.

I need these features in my parser:

1. Parser should be a C++ class, defined in normal manner (a header and a cpp file)
2. Parser receives data from either an std::string or std::stringstream or a null-terminated char*.

I feel so confused. Should I use flex++/bisonc++ or flex/bison? And how to do that, satisfying above conditions?

Answer 1

There are flex/bison, flex++/bison++ and flexc++/bisonc++. I think it's best to pick one of these three pairs, instead of mixing/matching flex++ and bisonc++. Here are the user guides for Flexc++ and Bisonc++.

From the Flexc++ website:

Flexc++, contrary to flex and flex++, generates code that is explicitly intended for use by C++ programs. The well-known flex(1) program generates C source-code and flex++(1) merely offers a C++-like shell around the yylex function generated by flex(1) and hardly supports present-day ideas about C++ software development. Contrary to this, flexc++ creates a C++ class offering a predefined member function lex matching input against regular expressions and possibly executing C++ code once regular expressions were matched. The code generated by flexc++ is pure C++, allowing its users to apply all of the features offered by that language.

From the Bisonc++ website:

Bisonc++ is a general-purpose parser generator that converts a grammar description for an LALR(1) context-free grammar into a C++ class to parse that grammar. Once you are proficient with bisonc++, you may use it to develop a wide range of language parsers, from those used in simple desk calculators to complex programming languages. Bisonc++ is highly comparable to the program bison++, written by Alain Coetmeur: all properly-written bison++ grammars ought to be convertible to bisonc++ grammars after very little or no change. Anyone familiar with bison++ or its precursor, bison, should be able to use bisonc++ with little trouble. You need to be fluent in using the C++ programming in order to use bisonc++ or to understand this manual.

So flexc++/bisonc++ are more than just wrappers around the old flex/bison utilities. They generate complete C++ classes to be used for re-entrant scanning / parsing.

Answer 2

Flex can generate a reentrant C scanner. See Section 19 Reentrant C scanners in the Flex manual.

Similarly, Bison can generate a reentrant C parser. See Section 3.8.11 A Pure (Reentrant) Parser in the Bison manual for details.

Do you absolutely need to have a C++ parser and std::string/stringstream based parser data?

Have you looked at Boost.Spirit as an alternative?