didnt grab packet

[lalani () cs fsu edu]

Hi guys,
 This is code which has been modified from a program which is  
floating on the net.
 The output says didnt grab packet. I wonder why.
 I am giving the command 'a.out <filename>'
 The same file is read by 'tcpdump -r <filename>'
 Can someone say me why and how I can fix it.
 Thanks in advance.

 zubin


#include<stdio.h>
#include<stdlib.h>
#include <pcap.h>
#include<errno.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>
#include<netinet/if_ether.h>


int main(int argc, char **argv)
{
        int i;
        char *dev;
        char errbuf[PCAP_ERRBUF_SIZE];
        pcap_t* descr;
        const u_char *packet;
        struct pcap_pkthdr hdr;
        struct ether_header *eptr;
        u_char *ptr;
        dev = pcap_lookupdev(errbuf);

        if(dev == NULL)
        {
                printf("%s\n",errbuf);
                exit(1);
        }

        printf("DEV: %s\n",dev);

        descr = pcap_open_offline(argv[1],errbuf);

        if(descr == NULL)
        {
                printf("%s doesnt exist or is of corrupt format\n",argv[1]);
                exit(1);
        }


        packet = pcap_next(descr, &hdr);

        if(packet == NULL);
        {
                printf("Didnt grab packet %s\n",errbuf);
                exit(1);
        }

        return 0;
}


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