Re: %union in Bison

Davide Rizzo wrote:
> [ %union in bison with a C++ class doesn't work ]


> [Bison generates C code, not C++ code. -John]


The code produced by Bison (at least, from version 1.28) *is* compilable
as C++ code. With a little bit of preprocessor magic and an innocuous hack
to the parser skeleton in bison.simple you can even use the generated
yyparse() function as a class member function:


    -- use the %pure_parser directive in your grammar


    -- near the top of your grammar, in the user-code %{ ... %} section, write:
            #ifdef yyparse
            # undef yyparse
            #endif
            #define yyparse(parms) MYCLASS::yy_parse(parms)


    -- comment out the block in bison.simple which begins with a comment
          about preventing warnings with -Wstrict-prototypes:
            /* Prevent warning if -Wstrict-prototypes. */
            #ifdef __GNUC__
            #ifdef YYPARSE_PARAM
            int yyparse (void *);
            #else
            int yyparse (void);
            #endif
            #endif
          If you also use C *and* -Wstrict-prototypes, you can enclose this
          block in an "#ifndef __cplusplus" instead.


C++ won't allow you to place an STL string (or any other instance of
a class with a constructor) into the %union. You could use a "string *",
but then you'll have to delete the string instances.




Greetings, Jim


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mailto:j.rauser@science-factory.com Unter Käster 1
Tel: +49 221 277 399 204 50667 Cologne, Germany

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