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

Sheaves

did you try to add -lfl at the end instead of beginning? – Cetus

okay, i will post that as answer. – Cetus

Answer 1

add -lfl at the end instead of beginning.

Cetus

Answer 2

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

Distillation

Answer 3

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.

Partizan

Answer 4

My solution was:

sudo apt-get install flex

Accept

Please explain how you had already generated a lex.yy.c file without having flex already installed. – Partizan

Answer 5

I created a file addon.c

int yywrap (void )
{
    return 1;
}

and added it to the target.

Arabelle