请用C语言实现指定网卡指定端口指定抓包数量并存到pcap文件的程序

好的，以下是一个简单的使用libpcap库实现指定网卡、指定端口、指定抓包数量并存储到pcap文件的C语言程序：

#include <pcap.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define SNAP_LEN 65535
#define SIZE_ETHERNET 14
#define SIZE_TCP 20

void packet_handler(u_char *args, const struct pcap_pkthdr *header, const u_char *packet);

int main(int argc, char *argv[]) {
    char errbuf[PCAP_ERRBUF_SIZE];
    pcap_t *handle;
    char *dev = argv[1]; // 网卡名
    uint16_t port = atoi(argv[2]); // 端口号
    int packet_count = atoi(argv[3]); // 抓包数量
    char *pcap_file = argv[4]; // pcap文件名
    bpf_u_int32 net = 0;
    bpf_u_int32 mask = 0;
    struct bpf_program fp;
    char filter_exp[100];
    sprintf(filter_exp, "tcp port %d", port);

    // 获取网络号和掩码
    if (pcap_lookupnet(dev, &net, &mask, errbuf) == -1) {
        fprintf(stderr, "Couldn't get netmask for device %s: %s\n", dev, errbuf);
        net = 0;
        mask = 0;
    }

    // 打开网络接口
    handle = pcap_open_live(dev, SNAP_LEN, 1, 1000, errbuf);
    if (handle == NULL) {
        fprintf(stderr, "Couldn't open device %s: %s\n", dev, errbuf);
        exit(EXIT_FAILURE);
    }

    // 编译过滤器
    if (pcap_compile(handle, &fp, filter_exp, 0, net) == -1) {
        fprintf(stderr, "Couldn't parse filter %s: %s\n", filter_exp, pcap_geterr(handle));
        exit(EXIT_FAILURE);
    }

    // 设置过滤器
    if (pcap_setfilter(handle, &fp) == -1) {
        fprintf(stderr, "Couldn't install filter %s: %s\n", filter_exp, pcap_geterr(handle));
        exit(EXIT_FAILURE);
    }

    printf("Capturing packets on %s, port %d...\n", dev, port);

    // 打开pcap文件
    pcap_dumper_t *dumper = pcap_dump_open(handle, pcap_file);
    if (dumper == NULL) {
        fprintf(stderr, "Couldn't open pcap file %s: %s\n", pcap_file, pcap_geterr(handle));
        exit(EXIT_FAILURE);
    }

    // 开始抓包
    pcap_loop(handle, packet_count, packet_handler, (u_char *)dumper);

    // 关闭pcap文件
    pcap_dump_close(dumper);

    // 关闭网络接口
    pcap_close(handle);

    printf("Done.\n");

    return 0;
}

void packet_handler(u_char *args, const struct pcap_pkthdr *header, const u_char *packet) {
    static int packet_num = 0;
    pcap_dump(args, header, packet);
    printf("Packet %d captured.\n", ++packet_num);
}

程序使用方法：在命令行中输入`./program eth0 80 100 packets.pcap`，其中`eth0`为网卡名，`80`为端口号，`100`为抓包数量，`packets.pcap`为pcap文件名。程序将会抓取指定网卡上指定端口的指定数量的数据包，并将其存储到指定的pcap文件中。