Re: Parsing '\x00' -- appears to be the only thing preventing parsing binary data

[Stephen Taylor]

That appears to give me an error in lex:

%option noyywrap                                                                
                                                  
                                                                                
                                                  
%%                                                                              
                                                  
\x00  { return ZERO; }                                                          
                                                  
.|\n  { return *yytext; }                                                       
                                                  
%%                                                                              
                                                  
       

—
Error:

flex -8 gmr.l
gcc  -c lex.yy.c
gmr.l: In function ‘yylex’:
gmr.l:2:10: error: ‘ZERO’ undeclared (first use in this function); did you mean 
‘EIO’?
 \x00  { return ZERO; }
          ^~~~
          EIO
gmr.l:2:10: note: each undeclared identifier is reported only once for each 
function it appears in
Makefile:13: recipe for target 'lex.yy.o' failed
make: *** [lex.yy.o] Error 1


Bison likes it.
Tried quoting the \x00 but thats not right it appears.



> On Mar 30, 2021, at 16:15, Chris verBurg <cheetomonster@gmail.com> wrote:
> 
> 
> I don’t know how you’ve set up your flex/bison interface, but I’m guessing 
> from your quoting that you have flex return each character as a token?  Can 
> you special-case 0 to not have the token value 0?  That is, flex does this:
> 
> \x00  { return ZERO; }
> 
> And then in your grammar:
> 
> %token ZERO
> 
> and use ZERO instead of ‘\x00’?
> 
> (Note: typed this on a phone..not 100% sure the syntax is right.)
> 
> -Chris
> 
> 
>> On Mar 30, 2021, at 12:37 PM, Stephen Taylor via Users list for the GNU 
>> Bison parser generator <help-bison@gnu.org> wrote:
>> 
>> I am trying to parse binary files and obviously need to write rules that 
>> include the 8-bit value 0x00 — flex appears to allow me to obtain an 8-bit 
>> scanner using the -8 option. I seem to be able to use ‘\x01’ to ‘\xFF’ for 
>> individual terminal symbols in Bison rules. Unfortunately, ‘\x00’ is used to 
>> denote end of input. Looking at the output tables, there appears to be no 
>> real reason to do this (other than convenience) and I am wondering if anyone 
>> has a workaround? 
>> Thanks !
>> Steve
>> 
>> 
>> 
>> 
>

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