Re: Reentrant Flex and Bison

Our workaround (don't want to call it a solution):


File Lexer.h:
      // Declaration of the lexer class
      class LexerClass : public yyFlexLexer {


      [...]


          private:


              // A pointer to the union that holds the associated value to
              // the returned token
              char** lexerlval;


              // The method flex generates
              yylex ();


              // The method the bison parser expects: 1. variante
              yylex (void* lvalp) {
                  lexerlval = &((static_cast<YYSTYPE*>(lvalp)));
                  return yylex();
              }


              // The method the bison parser expects: 2. variante
              yylex (YYSTYPE* lvalp) {
                  lexerlval = &lvalp;
                  return yylex();
              }


      }


File lexer.l:
    // a rule:
    {match_anything} { lexerlval* =3D strdup(YYText()); return ANYTOKEN; }




Of course you can have more than "char*" for the associated
values. And you can let bison generate two kinds of yylex:
yylex(void*) or yylex(YYSTYPE*). In the latter case you don't need the
static_cast.


Burkhard




richard.lanyon@wadham.oxford.ac.uk (Richard Lanyon) writes:


> I'm trying to get a lexer + parser combination going using flex and bison.
> The problem is that I seem to have to declare yylex (as int yylex()) in
> the C declarations section of the bison grammar file.
> This wouldn't necessarily be a problem (except that I'm sure I shouldn't
> /have/ to) except that if I then want to make a re-entrant (aka "pure")
> parser, yylex needs to be declared as
> int yylex(YYSTYPE *lvalp)
> and YYSTYPE isn't defined in the C declarations section of the Bison
> grammar file - it only comes into being in the Bison declaration section.

Return to the comp.compilers page.
Search the comp.compilers archives again.