How to access multiple pcap files offline and extract an ip address?

I'm trying to access multiple .pcap files from a directory and extract the source (and destination) IP address of each.

The code (below) works when I pass a .pcap file by command line.

Thanks for help in solving this.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <pcap.h> //library for parsing pcap files


#define SIZE_ETHERNET 14
#define ETHER_ADDR_LEN  6


/* Ethernet header */
    struct sniff_ethernet {
    u_char ether_dhost[ETHER_ADDR_LEN]; /* Destination host     address */
    u_char ether_shost[ETHER_ADDR_LEN]; /* Source host address */
    u_short ether_type; /* IP? ARP? RARP? etc */
};

/* IP header */
struct sniff_ip {
    u_char ip_vhl;      /* version << 4 | header length >> 2 */
    u_char ip_tos;      /* type of service */
    u_short ip_len;     /* total length */
    u_short ip_id;      /* identification */
    u_short ip_off;     /* fragment offset field */
#define IP_RF 0x8000        /* reserved fragment flag */
#define IP_DF 0x4000        /* dont fragment flag */
#define IP_MF 0x2000        /* more fragments flag */
#define IP_OFFMASK 0x1fff   /* mask for fragmenting bits */
    u_char ip_ttl;      /* time to live */
    u_char ip_p;        /* protocol */
    u_short ip_sum;     /* checksum */
    struct in_addr ip_src;
    struct in_addr ip_dst; /* source and dest address */
};
#define IP_HL(ip)       (((ip)->ip_vhl) & 0x0f)
#define IP_V(ip)        (((ip)->ip_vhl) >> 4)

/* TCP header */
struct sniff_tcp {
    u_short th_sport;   /* source port */
    u_short th_dport;   /* destination port */
    u_int32_t th_seq;       /* sequence number */
    u_int32_t th_ack;       /* acknowledgement number */

    u_char th_offx2;    /* data offset, rsvd */
#define TH_OFF(th)  (((th)->th_offx2 & 0xf0) >> 4)
    u_char th_flags;
#define TH_FIN 0x01
#define TH_SYN 0x02
#define TH_RST 0x04
#define TH_PUSH 0x08
#define TH_ACK 0x10
#define TH_URG 0x20
#define TH_ECE 0x40
#define TH_CWR 0x80
#define TH_FLAGS (TH_FIN|TH_SYN|TH_RST|TH_ACK|TH_URG|TH_ECE|TH_CWR)
    u_short th_win;     /* window */
    u_short th_sum;     /* checksum */
    u_short th_urp;     /* urgent pointer */
};

void main(int argc, char *argv[])
{

//get filestring
 string *filename = "/HiWi/pcap_files/*.pcap";

 //error buffer
 char errbuff[PCAP_ERRBUF_SIZE];

 //open file and create pcap handler
 pcap_t * handler = pcap_open_offline(filename.c_str(), errbuff);

 //The header that pcap gives us
struct pcap_pkthdr *header;

//The actual packet
const u_char *packet;

  int packetCount = 0;
  int i;

  //write to file
  FILE *fp = fopen ( "result.txt", "w" ) ;

  //tcp info
const struct sniff_ethernet *ethernet; /* The ethernet header */
const struct sniff_ip *ip; /* The IP header */
const struct sniff_tcp *tcp; /* The TCP header */
u_int size_ip;
u_int size_tcp;

while (pcap_next_ex(handler, &header, &packet) >= 0)
{
    // Show the packet number
    printf("Packet # %i\n", ++packetCount);
    fprintf(fp,"Packet # %i\n", packetCount);

    // Show the size in bytes of the packet
    printf("Packet size: %d bytes\n", header->len);
    fprintf(fp,"Packet size: %d bytes\n", header->len);

    // Show a warning if the length captured is different
    if (header->len != header->caplen)
        printf("Warning! Capture size different than packet size: %ld bytes\n", header->len);

    // Show Epoch Time
    printf("Epoch Time: %d:%d seconds\n", header->ts.tv_sec, header->ts.tv_usec);
    fprintf(fp,"Epoch Time: %d:%d seconds\n", header->ts.tv_sec, header->ts.tv_usec);

    ethernet = (struct sniff_ethernet*)(packet);
    ip = (struct sniff_ip*)(packet + SIZE_ETHERNET);
    size_ip = IP_HL(ip)*4;
    if (size_ip < 20) {
        printf("   * Invalid IP header length: %u bytes\n", size_ip);
        return;
    }
    tcp = (struct sniff_tcp*)(packet + SIZE_ETHERNET + size_ip);

    printf("src port: %d dest port: %d \n", tcp->th_sport, tcp->th_dport);
    fprintf(fp,"src port: %d dest port: %d \n", tcp->th_sport, tcp->th_dport);

    printf("src address: %s dest address: %s \n",  inet_ntoa(ip->ip_src),  inet_ntoa(ip->ip_dst));
    fprintf(fp,"src address: %s dest address: %s \n",  inet_ntoa(ip->ip_src),  inet_ntoa(ip->ip_dst));

    printf("seq number: %u ack number: %u \n", (unsigned int)tcp-> th_seq, (unsigned int)tcp->th_ack);
    fprintf(fp,"seq number: %u ack number: %u \n", (unsigned int)tcp-> th_seq, (unsigned int)tcp->th_ack);

    // Add two lines between packets
    printf("\n");
    fprintf(fp,"\n");
}
fclose (fp);
 return;
}

string *filename = "/HiWi/pcap_files/*.pcap";

When you pass that string from the command line it is likely your shell does globbing for you and the program actually ends up with a few real paths. On the other hand pcap_open_offline expects real paths - does no globbing - so it just reports "No, I didn't find that file called *.pcap".

You will have to do globbing yourself, perhaps using glob(3). In essence it will give you a glob_t with a number of paths. You simply need to do pcap_open_offline each file in turn and so on. I suggest you make a function taking a filename that does all this so you can call it for each file.