small program compile failed when using pcap, "undefined reference to `pcap_set"

["Arthur Chen" <iamarthur60 () hotmail com>]

this small trying program can not compile, It said undefined reference to 
`pcap_set_datalink', but this function prototype was included in pcap.h and 
was implemented in pcap.c! Any idea?

    This is the error message:

[root@ arthur]# gcc -lpcap -o pcap_test.o pcap_test.c
/tmp/ccViVFVU.o(.text+0xbb): In function `main':
: undefined reference to `pcap_set_datalink'
collect2: ld returned 1 exit status
[root@ arthur]#


     the source file is:

#include <stdio.h>
#include <pcap.h>
//#include <pcap_int.h>
extern int      pcap_set_datalink(pcap_t *, int);
   int main()
   {
       pcap_t *handle;                       /* Session handle */
//      char *dev;                            /* The device to sniff on */
       char errbuf[PCAP_ERRBUF_SIZE];        /* Error string */
       struct bpf_program filter;            /* The compiled filter */
//      char filter_app[] = "port 23";        /* The filter expression */
       char filter_app[] = "ether[11]=0xcb || (ether[5]=0xcb)";
       bpf_u_int32 mask;                     /* Our netmask */
       bpf_u_int32 net;                      /* Our IP */
       struct pcap_pkthdr header;            /* The header that pcap gives 
us */
       const u_char *packet;                 /* The actual packet */
       /* Define the device */
//        dev = pcap_lookupdev(errbuf);
char dev[]="eth0";
int errCode=0;

bpf_u_int32 counter=0;
printf("the dev=%s\n",dev);

       /* Find the properties for the device */
       pcap_lookupnet(dev, &net, &mask, errbuf);
        /* Open the session in promiscuous mode */
       handle = pcap_open_live(dev, BUFSIZ, 1, 0, errbuf);
        //printf("The data link is %d",(pcap_datalink(handle)));
pcap_set_datalink(handle, DLT_PPP_ETHER);

if (errCode)
        printf("Set data link failed, error code=%d",errCode);
else
        printf("Set data link succeeded, ");

        /* Compile and apply the filter */
//        pcap_compile(handle, &filter, filter_app, 0, net);
       pcap_compile(handle, &filter, filter_app, 0, net);
        pcap_setfilter(handle, &filter);
       /* Grab a packet */

        packet = pcap_next(handle, &header);
       /* Print its length */
       printf("Jacked a packet with length of [%d]\n", header.len);
       /* And close the session */
for (; counter<header.len; counter++)
        printf("%3x", *(packet+counter));

        pcap_close(handle);

       return(0);
   }

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