Valid regular expression for identifier using flex

manpreet Best Answer 2 years ago

I'm trying to make a regular expression that will only work when a valid identifier name is given, using flex (the name cannot start with a number). I'm using this code :

%{
#include 
#include 
#include 

%}

%%
"if"                        { printf("IF "); }
[a-zA-Z_][a-zA-Z_0-9]*      { printf("%s ", yytext); }

%%

int main() {
    yylex();
} 

but it is not working. how to make sure that flex accepts only a valid identifier?

When I provide the input:

if
abc
9abc

I see the following output:

IF
abc
9abc

but I expected:

IF
abc
(nothing)