程序代码：

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

int main(int argc, char **argv) {
    char *dev; /* name of the device to use */
    char *net; /* dot notation of the network address*/
    char *mask; /* dot notation of the network mask*/
    int ret;
    char errbuf[PCAP_ERRBUF_SIZE];
    bpf_u_int32 netp; /* ip */
    bpf_u_int32 maskp; /* subnet mask */
    struct in_addr addr;

    /* ask pcap to find a valid device for use to sniff on */
    dev = pcap_lookupdev(errbuf);

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

    /* print out device name */
    printf("DEV: %s\n",dev);

    /* ask pcap for the network address and mask of the device */
    ret = pcap_lookupnet(dev, &netp, &maskp, errbuf);
    if(ret == -1) {
        printf("%s\n",errbuf);
        exit(1);
    }

    addr.s_addr = netp;
    net = inet_ntoa(addr);

    if(net == NULL) {
        perror("inet_ntoa");
        exit(1);
    }
    printf("NET: %s\n",net);

    addr.s_addr = maskp;
    mask = inet_ntoa(addr);

    if(mask == NULL) {
        perror("inet_ntoa");
        exit(1);
    }
    printf("MASK: %s\n",mask);
    
    return 0;
}