flex: undefined reference to `yywrap' only when compiling/linking separately

Question

I've been learning to use Flex (the lexical analyser) and I've been compiling with the following command:

gcc -lfl -o test lex.yy.c

and all is well. However, I want to link it with other files, so I compile and link it separately with

gcc -c lex.yy.c

followed by

gcc -lfl -o test lex.yy.o

but gcc tells me that there is an undefined reference to yywrap(). So, what's going on here?

I'm using Flex 2.5.35, gcc 4.7.2 and ld 2.22

did you try to add `-lfl` at the end instead of beginning? – Raj Dec 26 '12 at 15:55 — Raj, Dec 26 '12 at 15:55
okay, i will post that as answer. – Raj Dec 28 '12 at 12:47 — Raj, Dec 28 '12 at 12:47

score 22 · Accepted Answer · answered Dec 28 '12 at 12:47

22

add -lfl at the end instead of beginning.

answered Dec 28 '12 at 12:47

Raj

score 4 · Answer 2 · edited Nov 04 '14 at 12:32

4

Use gcc lex.yy.c -ll. Otherwise it will yield an undefined reference to yywrap.

edited Nov 04 '14 at 12:32

honk

answered Nov 04 '14 at 11:51

kartik7153

score 2 · Answer 3 · answered Jan 12 '13 at 02:17

2

Alternatively, if you don't want to use the library, just #define yywrap() 1 in your .l file, or provide a yywrap() method that returns 1.

It's documented.

answered Jan 12 '13 at 02:17

user207421

score 1 · Answer 4 · answered May 23 '13 at 13:02

1

My solution was:

sudo apt-get install flex

answered May 23 '13 at 13:02

Hugo

7

Please explain how you had already generated a lex.yy.c file without having flex already installed. – user207421 Oct 04 '14 at 10:22

score 1 · Answer 5 · answered Oct 24 '16 at 22:04

1

I created a file addon.c

int yywrap (void )
{
    return 1;
}

and added it to the target.

answered Oct 24 '16 at 22:04

Th. Thielemann

5 Answers5