Re: Using Bison parser with C++ code

> Does anyone know of some good online examples for integrating a
> bison/yacc compiler into a C++ program. I'm new at this parser
> writing game and needless to say, the learning curve is steep.


You can simply incorporate C++ code into the bison actions. For example:
%{
// Include definition of the Abstract Syntax Tree class
#include "ASTree.h"


typedef ASTree* ASTreePtr;
#define YYSTYPE ASTreePtr
%}
%left '+' '-'
%token NUM
%%
start: expr {$1->printTree(); }
expr : expr '+' expr {$$ = new ASTree('+', $1, $2); }
          | expr '-' expr {$$ = new ASTree('-', $1, $2); }
          | NUM {$$ = new ASTree(NUM, atoi(yytext)); }


And so forth. (Note this might not compile exactly as is, I just typed
it out of my head, but I hope you get the general idea.)


Bison will produce a C file containing these C++ statements in the
appropriate places. You must simply tell your compiler to compile it
as a C++ file. For example, in your makefile you might do:


grammar.o : grammar.y
  bison -d grammar.y -o grammar.cc


in UNIX, or in Visual C++ you would set the special build instructions
to something like:


  bison -d $(InputName).y -o $(ProjDir)\$(InputName).cpp
  mv "$(InputName).cpp.h" $(InputName).h


(I use mv, but you can also use ren. For some reason the .h file gets
a screwed up name. This might also be true in unix, I haven't tried.)


The bison parse table processing algorithm is already compatible with
C++.


You can then simply call yyparse as normal. If you want to incorporate
the parsing into a class, most likely you will have to build a pure
parser, as documented in the bison manual.


Note I use an out of date version of bison: 1.24, but I am sure later
versions incorporate these features.


HTH.

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