在虚拟机里用C++语言实现ping功能

实现ping功能需要使用socket编程和icmp协议。以下是一个简单的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/time.h>

#define PACKET_SIZE 64  // ICMP包大小
#define MAX_WAIT_TIME 5  // 最大等待时间

// ICMP包头部结构体定义
struct icmp_packet {
    struct icmphdr hdr;
    char msg[PACKET_SIZE-sizeof(struct icmphdr)];
};

// 计算校验和
unsigned short calc_checksum(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包
void send_packet(int sockfd, struct sockaddr *addr, int seq) {
    struct icmp_packet packet;
    struct timeval tv;
    packet.hdr.type = ICMP_ECHO;
    packet.hdr.code = 0;
    packet.hdr.un.echo.id = getpid();
    packet.hdr.un.echo.sequence = seq;
    gettimeofday(&tv, NULL);
    memcpy(packet.msg, &tv, sizeof(tv));
    packet.hdr.checksum = calc_checksum((unsigned short*)&packet, PACKET_SIZE);
    sendto(sockfd, &packet, PACKET_SIZE, 0, addr, sizeof(*addr));
}

// 接收icmp包
int recv_packet(int sockfd, struct sockaddr *addr, int seq, struct timeval *tv) {
    struct icmp_packet packet;
    socklen_t addrlen = sizeof(*addr);
    fd_set readfds;
    struct timeval timeout;
    int ret, n;
    while (1) {
        FD_ZERO(&readfds);
        FD_SET(sockfd, &readfds);
        timeout.tv_sec = MAX_WAIT_TIME;
        timeout.tv_usec = 0;
        ret = select(sockfd+1, &readfds, NULL, NULL, &timeout);
        if (ret == -1) {
            perror("select");
            return -1;
        } else if (ret == 0) {
            printf("Request timeout for icmp_seq %d\n", seq);
            return -1;
        } else {
            n = recvfrom(sockfd, &packet, PACKET_SIZE, 0, addr, &addrlen);
            if (n < 0) {
                perror("recvfrom");
                return -1;
            }
            if (packet.hdr.type == ICMP_ECHOREPLY && packet.hdr.un.echo.id == getpid() && packet.hdr.un.echo.sequence == seq) {
                gettimeofday(tv, NULL);
                printf("%d bytes from %s icmp_seq=%d ttl=%d time=%.3f ms\n", n, inet_ntoa(((struct sockaddr_in*)addr)->sin_addr), seq, packet.hdr.un.echo.id, (double)(tv->tv_sec*1000+tv->tv_usec/1000)-(double)(*(struct timeval*)packet.msg).tv_sec*1000-(double)(*(struct timeval*)packet.msg).tv_usec/1000);
                return 0;
            }
        }
    }
}

int main(int argc, char *argv[]) {
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <hostname>\n", argv[0]);
        exit(1);
    }
    int sockfd;
    struct sockaddr_in addr;
    struct hostent *host;
    int seq = 1;
    struct timeval tv_begin, tv_end;
    double time_sum = 0;
    int cnt = 0;
    sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
    if (sockfd < 0) {
        perror("socket");
        exit(1);
    }
    host = gethostbyname(argv[1]);
    if (host == NULL) {
        fprintf(stderr, "Unknown host %s\n", argv[1]);
        exit(1);
    }
    addr.sin_family = AF_INET;
    addr.sin_addr = *((struct in_addr*)host->h_addr);
    printf("PING %s (%s) %d bytes of data.\n", argv[1], inet_ntoa(addr.sin_addr), PACKET_SIZE);
    while (1) {
        gettimeofday(&tv_begin, NULL);
        send_packet(sockfd, (struct sockaddr*)&addr, seq);
        if (recv_packet(sockfd, (struct sockaddr*)&addr, seq, &tv_end) == 0) {
            time_sum += (double)(tv_end.tv_sec*1000+tv_end.tv_usec/1000)-(double)(tv_begin.tv_sec*1000+tv_begin.tv_usec/1000);
            cnt++;
        }
        sleep(1);
        seq++;
    }
    close(sockfd);
    return 0;
}

在虚拟机里运行该程序需要先安装gcc编译器和相关库：

sudo apt-get update
sudo apt-get install build-essential
sudo apt-get install libnet-dev

然后使用以下命令编译并运行程序：

gcc ping.c -o ping
sudo ./ping <hostname>

其中`<hostname>`为要ping的主机名或IP地址。注意需要使用sudo权限运行程序，因为需要使用原始套接字。