关于 error LNK2019 无法解析的外部符号,该如何解决

#ifdef _MSC_VER
//*
// * we do not want the warnings about the old deprecated and unsecure CRT functions
// * since these examples can be compiled under *nix as well
// */
#define _CRT_SECURE_NO_WARNINGS
#endif

#include "pcap.h"

#ifndef WIN32
    #include <sys/socket.h>
    #include <netinet/in.h>
#else
    #include <winsock.h>
#endif

// Function prototypes
void ifprint(pcap_if_t *d);
char *iptos(u_long in);
char* ip6tos(struct sockaddr *sockaddr, char *address, int addrlen);

int main()
{
    pcap_if_t *alldevs;
    pcap_if_t *d;
    char errbuf[PCAP_ERRBUF_SIZE+1];

    /* Retrieve the device list */
    if(pcap_findalldevs(&alldevs, errbuf) == -1)
    {
        fprintf(stderr,"Error in pcap_findalldevs: %s\n", errbuf);
        exit(1);
    }

    /* Scan the list printing every entry */
    for(d=alldevs;d;d=d->next)
    {
        ifprint(d);
    }

    /* Free the device list */
    pcap_freealldevs(alldevs);

    return 1;
}

/* Print all the available information on the given interface */
void ifprint(pcap_if_t *d)
{
  pcap_addr_t *a;
  char ip6str[128];

  /* Name */
  printf("%s\n",d->name);

  /* Description */
  if (d->description)
    printf("\tDescription: %s\n",d->description);

  /* Loopback Address*/
  printf("\tLoopback: %s\n",(d->flags & PCAP_IF_LOOPBACK)?"yes":"no");

  /* IP addresses */
  for(a=d->addresses;a;a=a->next) {
    printf("\tAddress Family: #%d\n",a->addr->sa_family);

    switch(a->addr->sa_family)
    {
      case AF_INET:
        printf("\tAddress Family Name: AF_INET\n");
        if (a->addr)
          printf("\tAddress: %s\n",iptos(((struct sockaddr_in *)a->addr)->sin_addr.s_addr));
        if (a->netmask)
          printf("\tNetmask: %s\n",iptos(((struct sockaddr_in *)a->netmask)->sin_addr.s_addr));
        if (a->broadaddr)
          printf("\tBroadcast Address: %s\n",iptos(((struct sockaddr_in *)a->broadaddr)->sin_addr.s_addr));
        if (a->dstaddr)
          printf("\tDestination Address: %s\n",iptos(((struct sockaddr_in *)a->dstaddr)->sin_addr.s_addr));
        break;

      case AF_INET6:
       printf("\tAddress Family Name: AF_INET6\n");
#ifndef __MINGW32__ /* Cygnus doesn't have IPv6 */
        if (a->addr)
          printf("\tAddress: %s\n", ip6tos(a->addr, ip6str, sizeof(ip6str)));
#endif
        break;

      default:
        printf("\tAddress Family Name: Unknown\n");
        break;
    }
  }
  printf("\n");
}

/* From tcptraceroute, convert a numeric IP address to a string */
#define IPTOSBUFFERS    12
char *iptos(u_long in)
{
    static char output[IPTOSBUFFERS][3*4+3+1];
    static short which;
    u_char *p;

    p = (u_char *)&in;
    which = (which + 1 == IPTOSBUFFERS ? 0 : which + 1);
    sprintf(output[which], "%d.%d.%d.%d", p[0], p[1], p[2], p[3]);
    return output[which];
}

#ifndef __MINGW32__ /* Cygnus doesn't have IPv6 */
char* ip6tos(struct sockaddr *sockaddr, char *address, int addrlen)
{
    socklen_t sockaddrlen;

    #ifdef WIN32
    sockaddrlen = sizeof(struct sockaddr_in6);
    #else
    sockaddrlen = sizeof(struct sockaddr_storage);
    #endif

    if(getnameinfo(sockaddr,
        sockaddrlen,
        address,
        addrlen,
        NULL,
        0,
        NI_NUMERICHOST) != 0) address = NULL;

    return address;
}
#endif /* __MINGW32__ */