Re: about packet capture

[Erik de Castro Lopo <erikd+tcpdump () sensorynetworks com>]

On Tue, 3 Feb 2004 15:44:41 +1100 (EST)
Tao Peng <taop () ee mu oz au> wrote:

> Dear All,
>
> I am a rookie to network programming, and I am having troubles of compling
> a single code.
>
> The code is as follows:
> ******************************************************
> #include <stdio.h>
> #include <pcap.h>
> int main()
> {
>     char *dev, errbuf[PCAP_ERRBUF_SIZE];
>     dev = pcap_lookupdev(errbuf);
>     printf("Device: %s\n", dev);
>     return(0);
> }
> ******************************************************
>
> when I complie it using gcc, it gives me an error as follows:
> /var/tmp//cc95eETb.o: In function `main':
> /var/tmp//cc95eETb.o(.text+0x1e): undefined reference to `pcap_lookupdev'

This is a linker message not a compiler message (you can tell from the 
/var/tmp//*.o).

That means that the compiler had no problem with the C code, but that the
linker was not able to find the object file that defined 'pcap_lookupdev'.

> But I had my pcap.h included, and I don't know why. Can anyone help me
> about this?

You were probably doing something like:

     gcc program.c -o program


What you need is:

     gcc program.c -lpcap -o program

The "-lpcap" tells gcc to tell the linker to link to libpcap. If libpcap
is installed in a non-standard location you might need to do something
like this:

    gcc procgram.c -L/some/path -lpcap -o program

HTH,
Erik
-- 
------------------------------------------------------
[N] Erik de Castro Lopo, Senior Computer Engineer
[E] erik.de.castro.lopo () sensorynetworks com
[W] http://www.sensorynetworks.com
[T] +61 2 83022726 
[F] +61 2 94750316 
[A] L4/140 William St, East Sydney NSW 2011, Australia
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