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compile/linker problem with simple libipq code

For some reason, my simply code is not linking, and I don't know why. The libipq library is there, it contains the functions which the linker says fail, so I'm at a loss. Hopefully it's something stupid I'm overlooking. (=

Quote:

~/c/ipk> findlib --all ipq
/usr/lib/libipq.a
~/c/ipk> nm -a /usr/lib/libipq.a
libipq.o:
... snip ...
00000224 T ipq_create_handle
000004a4 T ipq_ctl
00000334 T ipq_destroy_handle
... snip ...
~/c/ipk> cat ipk.c

Code:

#include <linux/netfilter.h>

#include <libipq.h>



int main(int argc, char **argv)

{

  struct ipq_handle *ipqh;



  //  create a handle then destroy it, very simple

  ipqh = ipq_create_handle(0, PF_INET);

  if(ipqh) ipq_destroy_handle(ipqh);



  return 0;

}

~/c/ipk> gcc -L/usr/lib -lipq -o ipk ipk.c
/tmp/ccCxaG2d.o(.text+0x18): In function `main':
: undefined reference to `ipq_create_handle'
/tmp/ccCxaG2d.o(.text+0x2f): In function `main':
: undefined reference to `ipq_destroy_handle'
collect2: ld returned 1 exit status

Nothing seems out of place.
Anyone have an idea?

And how exactly are you building your test program? For the linking to be successful, two conditions must be met: The library containing the symbol must be in the directories searched by the linker and you must explicitly tell the linker to link the library.

If you'll look right below the segment of code, I showed the
gcc line I ran to attempt compilation/linking.

Although unnecessary, I included -L/usr/lib (where the
libipq library is housed).

The only thing that I am thinking is that maybe the linker is
looking for the shared library, which I don't have installed.

I guess I'll see about compiling it. Maybe that's the problem.

------ edit ------------

Looks like the install package only makes static libs.
Oh well, it was a thought.

Nevermind, I see it now.

Try this makefile:

Code:

CC = gcc

CFLAGS = -Wall -W -c -o

LDFLAGS = -lipq -o $(EXEC)

OBJECTS = ipq_test.o

EXEC = ipq_test



all: $(OBJECTS)

\t$(CC) $^ $(LDFLAGS)



%.o: %.c

\t$(CC) $(CFLAGS) $@ $<

Replace \t with tabs and file names as appropriate

I was too quick to reply. Please see my edited version.

Thanks for the heads up and makefile example. However, I found my error. I knew that order was very important to gcc, but didn't realize that it would affect my prog like this.
Basically, -lipq needs to come AFTER the .c source. Don't ask me why, but when I compile it as:

Quote:

gcc -o ipk ipk.c -lipq

it works just fine...

::shaking head::

Yeah, that's what I suspected and therefore gave you a Makefile (I always use Makefiles) that I knew would work. In your previous command line you were passing the library option to the compiler, not the linker.

Quote:

Originally posted by Hivemind
In your previous command line you were passing the library option to the compiler, not the linker.

That's what -l is for, providing libraries to link in, which the compiler provides the linker.

Per gcc's man page:

Quote:

-l library
Search the library named library when linking
... snip ...
The linker searches a standard list of directories for the library, which is actually a file named libli-
brary.a. The linker then uses this file as if it had been specified precisely by name.
...snip...

Anyway, it worked. This order thing shows that I haven't coded in C for a while. (=