FLEX Cannot build lex.yy.c

Question

Downloaded flex-2.5.37.tar.gz

Unpacked and followed INSTALL's instructions: ./configure + make + make install

In a new folder, I've written a file example.l containing:

%{
int a = 0, b = 0;
%}

%%
\n   ++a; ++b;
.    ++b;

%%
int main()
{
     yylex();
     printf("%d - %d", a, b);
}

which is a basic example from their website. Counting lines and characters in a file.

In a terminal, I ran flex example.l. It generated lex.yy.c

After that:
- gcc lex.yy.c -o lexyy: Throws undefined symbols for architecture x86_64
- gcc lex.yy.c -lfl: ld: library not found for -lfl
- gcc lex.yy.c -ll: Generates a.out, but when I run it against a file, it doesn't work (prints "0 - 0").

It seems that I can't get this damn file to compile. How does it know where to find the necessary libraries? Shouldn't the linking work from here (this current folder)?

It's a bit depressing that I can't get the simplest of examples going.

Answer 1

Alright. So it turns out I was missing a parameter named %option noyywrap, which goes here:

%{
int a = 0, b = 0;
%}

%option noyywrap

%%
\n   ++a; ++b;
.    ++b;
...

Apparently this tells FLEX that there's only one source file. So it's not a gcc issue, it was a FLEX config problem.

Thank you all for taking the time to read the question. Hope this helps anyone else.