Re: Very basic question about Flex

Now i've changed my rules to include whitespace and then the

[a-zA-Z]+ rule. The code is now:

%{
/**
  * First example program for flex
  *
  */
#include <stdio.h>
#include <stdlib.h>

%}
%%

is |
am |
are |
where |
was |
be |
being |
been |
do |
does |
did |
should |
can |
could |
has |
have |
had |
go { printf("%s is a verb\n", yytext); }

[ ]+[a-zA-Z]+ { printf("%s is not a verb", yytext); }

.|\n { ECHO; /* normal default anyway */ }

%%

int main(int argc, char **argv)
{
     yylex();
}

gut when i try to compile:

$flex test1.l

$gcc lex.yy.c -o test -Wall

i get:

lex.yy.c:1192:16: warning: ‘input’ defined but not used [-Wunused-function]
      static int input  (void)
                 ^~~~~
lex.yy.c:1149:17: warning: ‘yyunput’ defined but not used 
[-Wunused-function]
      static void yyunput (int c, char * yy_bp )
                  ^~~~~~~
/tmp/ccAD7IfT.o: In function `yylex':
lex.yy.c:(.text+0x4e6): undefined reference to `yywrap'
/tmp/ccAD7IfT.o: In function `input':
lex.yy.c:(.text+0x10f3): undefined reference to `yywrap'
collect2: error: ld returned 1 exit status


What includes do i need and how to get the warning away ?


best regards!







On 22.02.19 16:20, Jannick wrote:
> On Fri, 22 Feb 2019 15:00:51 +0100, [email protected] wrote:
>
> If you replace
>
>> [a-zA-Z]+ { printf("%s is not a verb", yytext); }
> by
>         [a-zA-Z]+ printf("'%s' is not a verb\n", yytext);
>
> you will see that the scanner does exactly what it is expected to do, since the line
>   
>> .|\n { ECHO; /* normal default anyway */ }
> makes it print any character (inkl. '\n') not in [a-zA-Z] to stdout.
>
>> Now my question is when i enter one of the verbs it's working normaly like
>> expected, but when i enter for example 234someword i also get the
>> messsage %s is not a verb but i've no rule saying that
> Well, things are printed in different bits to stdout as you might think in the first place:  The scanner prints each of the leading integers applying the last rule to each of them, then it pushes 'someword' through the [a-zA-Z]+ rule.
>
> If you apply the suggested change above, you'll see the difference.  And if in addition you replace 'ECHO' (which is a C macro) by a printf statement with some enclosing tags around the character and a trailing newline, it might be easier to guess what is happening behind the scenes.
>
> BTW: Not sure if this is the right place to address pure flex issues, but I leave it with others to judge on this.
>
> HTH.
> J.
>
>
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>
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