[vox-tech] Reg lex and flex compatibilty

[Jeff Newmiller]

On Fri, 4 Jul 2003, Muthumeena M wrote:

> 
> Hi ,
> Right now am porting an application which has few lex and yacc files from
> solaris to linux.
> 
> The application has no problem in solaris whereas when i compile the same
> in linux, it is getting stuck at the compilation of the file generated by
> lexer i.e the lex.yy.c file
> 
> The lex output (lex.yy.c) are also quite different in solaris and linux.
> 
> The compilation errors are
> 1. In function `unsigned char input()':
> `yysptr' undeclared (first use this  function). it goes on to many other
> undeclared errors.
> 
> For this there were no variables declared in the file.l (lex input file).
> Solaris had delared on its own, whereas in case of linux error was coming
> in yy.c.
> So i have manually declared in case of linux.
> I do not know the reason why this incompatibility is there.

One of the few incompatibilities betwee lex and flex is that flex does not
allow redefinition of "input" and "output" the same way lex does.  There
is an equivalent way to redefine input using YY_INPUT.

http://www.esiee.fr/~coupriem/Flex/flex_5.html
http://www.esiee.fr/~coupriem/Flex/flex_2.html

> 2. After the manual declaration of variables now it is giving
> "previous declaration of int yywrap() with C++ linkage
> conflicts with new declaration with C Linkage"
> and many like this.
> 
> In makefile the options given are
> @lex -t -l $< | sed s/"^yylex"/"int yylex"/g | sed s/yy/${*F}/g > $*.yy.c
> 
> and gcc of the .yy.c file.

Well, when a programmer goes and mucks with the output from an
implementation of a translator, they are risking incompatibility with a
different implementation.  As the saying goes, "if it hurts, don't do
that."

Really... get rid of the sed calls and avoid making changes to the
interface definitions.  The code you are using is booby-trapped, and you
are just going to have to clean it out.

[...]

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