如何在C++中创建RAW TCP/IP数据包？

#include<iostream>
#include <cstring>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <arpa/inet.h>

int main() {
    int sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_TCP);
    if (sockfd < 0) {
        std::cerr << "Error: cannot create socket."<< std::endl;
        return 1;
    }

    // 设置目标IP地址和端口
    sockaddr_in dest_addr;
    memset(&dest_addr, 0, sizeof(dest_addr));
    dest_addr.sin_family = AF_INET;
    dest_addr.sin_port = htons(80);
    inet_pton(AF_INET, "127.0.0.1", &dest_addr.sin_addr);

    // 构建TCP数据包
    char packet[sizeof(struct iphdr) + sizeof(struct tcphdr)];
    struct iphdr *iph = (struct iphdr *)packet;
    struct tcphdr *tcph = (struct tcphdr *)(packet + sizeof(struct iphdr));

    // 填充IP头部
    iph->ihl = 5;
    iph->version = 4;
    iph->tos = 0;
    iph->tot_len = sizeof(packet);
    iph->id = htons(54321);
    iph->frag_off = 0;
    iph->ttl = 64;
    iph->protocol = IPPROTO_TCP;
    iph->check = 0;
    iph->saddr = inet_addr("192.168.1.2");
    iph->daddr = dest_addr.sin_addr.s_addr;

    // 填充TCP头部
    tcph->source = htons(12345);
    tcph->dest = htons(80);
    tcph->seq = htonl(1);
    tcph->ack_seq = 0;
    tcph->reserved = 0;
    tcph->doff = 5;
    tcph->fin = 0;
    tcph->syn = 1;
    tcph->rst = 0;
    tcph->psh = 0;
    tcph->ack = 0;
    tcph->urg = 0;
    tcph->window = htons(32767);
    tcph->check = 0;
    tcph->urg_ptr = 0;

    // 计算IP头部校验和
    iph->check = check_sum((unsigned short *)iph, sizeof(struct iphdr));

    // 发送数据包
    sendto(sockfd, packet, sizeof(packet), 0, (struct sockaddr *)&dest_addr, sizeof(dest_addr));

    close(sockfd);
    return 0;
}