implicit declaration

[Wolfgang Jeltsch]

Hello,

I found this question at least two times asked on this mailing list but not an 
answer for it. If I try to compile a Bison-generated C++ file with g++ I get 
the following messages:
    /usr/share/bison/bison.simple: In function `int yyparse()':
    /usr/share/bison/bison.simple:573: implicit declaration of function `int
        yylex(...)'
    /usr/share/bison/bison.simple:799: implicit declaration of function `int
        yyerror(...)'
How can I avoid this?

Wolfgang