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From: Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid>
Newsgroups: comp.compilers
Subject: How do I match empty lines with Flex?
Date: Fri, 4 Oct 2019 22:01:48 +0800
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Dear comp.compilers,

The following program matches lines in a text file, but ignores empty
lines.  Is there any way I can alter it so it returns something on empty
lines?

Is there a reason .* doesn't match zero characters in this case?

%option noyywrap noinput nounput

%{
#include <stdio.h>

     char *yylval;

%}


%%

..* { yylval = yytext; return 1; }
\n { yylineno += 1; }
<<EOF>> { return 0; }

%%

int main( int argc, char *argv[] )
{
     if ( argc > 1 ) {
         yyin = fopen( argv[ 1 ], "r" );

         while ( yylex() ) {
             printf( "%d: %s\n", yylineno, yylval );

         }
     }

     return 0;
}

--
Johann | email: invalid -> com | www.myrkraverk.com/blog/
I'm not from the Internet, I just work there. | twitter: @myrkraverk
[Flex never matches an empty string.
I expect a pattern like ^\n would do what you want. -John]