c++实现Ping程序

下面是一个简单的 C++ 实现 Ping 程序的示例代码：

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <unistd.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <netinet/ip_icmp.h>

using namespace std;

const int PACKET_SIZE = 4096;
const int ICMP_HEAD_SIZE = 8;
const int MAX_WAIT_TIME = 5; // 最大等待时间，单位秒
const int MAX_COUNT = 4; // 最大尝试次数

// 计算校验和
unsigned short CalcChecksum(unsigned short *addr, int len) {
    unsigned int sum = 0;
    while (len > 1) {
        sum += *addr++;
        len -= 2;
    }
    if (len == 1) {
        sum += *(unsigned char*)addr;
    }
    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);
    return (unsigned short)(~sum);
}

// 发送 ICMP 报文
int SendIcmpPacket(int sock_fd, const struct sockaddr *dest_addr, int seq) {
    char packet[PACKET_SIZE];
    memset(packet, 0, PACKET_SIZE);

    struct icmp *icmp_hdr = (struct icmp*)packet;
    icmp_hdr->icmp_type = ICMP_ECHO;
    icmp_hdr->icmp_code = 0;
    icmp_hdr->icmp_id = getpid();
    icmp_hdr->icmp_seq = seq;
    memset(icmp_hdr->icmp_data, 0xa5, PACKET_SIZE - ICMP_HEAD_SIZE);

    icmp_hdr->icmp_cksum = CalcChecksum((unsigned short*)icmp_hdr, PACKET_SIZE);

    int ret = sendto(sock_fd, packet, PACKET_SIZE, 0, dest_addr, sizeof(struct sockaddr));
    if (ret == -1) {
        cerr << "sendto error" << endl;
        return -1;
    }
    return 0;
}

// 接收 ICMP 报文
int RecvIcmpPacket(int sock_fd, struct timeval &tv, struct sockaddr *from_addr) {
    char packet[PACKET_SIZE];
    socklen_t addr_len = sizeof(struct sockaddr);

    int ret = recvfrom(sock_fd, packet, PACKET_SIZE, 0, from_addr, &addr_len);
    if (ret == -1) {
        cerr << "recvfrom error" << endl;
        return -1;
    }

    struct iphdr *ip_hdr = (struct iphdr*)packet;
    int ip_hdr_len = ip_hdr->ihl * 4;
    struct icmp *icmp_hdr = (struct icmp*)(packet + ip_hdr_len);
    int icmp_hdr_len = ret - ip_hdr_len;

    if (icmp_hdr->icmp_type == ICMP_ECHOREPLY && icmp_hdr->icmp_id == getpid()) {
        tv.tv_sec = time(NULL) - tv.tv_sec;
        cout << icmp_hdr_len << " bytes from " << inet_ntoa(((struct sockaddr_in*)from_addr)->sin_addr) << ": icmp_seq=" << icmp_hdr->icmp_seq << " time=" << tv.tv_sec << "s" << endl;
        return 0;
    }
    return -1;
}

// Ping 操作
int Ping(const char *ip_addr) {
    int sock_fd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
    if (sock_fd < 0) {
        cerr << "socket error" << endl;
        return -1;
    }

    struct sockaddr_in dest_addr;
    memset(&dest_addr, 0, sizeof(dest_addr));
    dest_addr.sin_family = AF_INET;
    dest_addr.sin_addr.s_addr = inet_addr(ip_addr);

    int seq = 0;
    int count = 0;
    while (count < MAX_COUNT) {
        if (SendIcmpPacket(sock_fd, (struct sockaddr*)&dest_addr, seq) == -1) {
            cerr << "SendIcmpPacket error" << endl;
            return -1;
        }

        struct timeval tv;
        gettimeofday(&tv, NULL);

        fd_set read_fds;
        FD_ZERO(&read_fds);
        FD_SET(sock_fd, &read_fds);

        struct timeval timeout;
        timeout.tv_sec = MAX_WAIT_TIME;
        timeout.tv_usec = 0;

        int ret = select(sock_fd + 1, &read_fds, NULL, NULL, &timeout);
        if (ret < 0) {
            cerr << "select error" << endl;
            return -1;
        } else if (ret == 0) {
            cout << "Request timeout for icmp_seq " << seq << endl;
        } else if (FD_ISSET(sock_fd, &read_fds)) {
            if (RecvIcmpPacket(sock_fd, tv, (struct sockaddr*)&dest_addr) == -1) {
                cerr << "RecvIcmpPacket error" << endl;
                return -1;
            }
        }

        seq++;
        count++;
        sleep(1);
    }
    close(sock_fd);
    return 0;
}

int main(int argc, char *argv[]) {
    if (argc != 2) {
        cerr << "Usage: " << argv[0] << " <ip address>" << endl;
        return -1;
    }
    if (Ping(argv[1]) == -1) {
        cerr << "Ping error" << endl;
        return -1;
    }
    return 0;
}

该程序使用了原始套接字进行 ICMP 报文的发送和接收，并采用了 select 函数进行超时等待。在主函数中，程序需要传入目标 IP 地址进行 Ping 操作。程序会尝试发送指定次数的 ICMP 报文，并等待回应，如果超时则输出“Request timeout”，如果收到回应则输出“icmp_seq=xx time=xx”，其中 xx 表示 ICMP 报文的序列号和延迟时间。