ping程序设计与实现jc++代码

以下是一个简单的 ping 程序的 C++ 代码实现：

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <ctime>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <unistd.h>

#define PACKET_SIZE 4096
#define MAX_WAIT_TIME 5
#define MAX_NO_PACKETS 3

using namespace std;

struct timeval tvsend, tvrecv;

int sockfd, datalen = 56;
char sendpacket[PACKET_SIZE], recvpacket[PACKET_SIZE];
int nsend = 0, nreceived = 0;
struct sockaddr_in dest_addr, from_addr;
pid_t pid;

void send_packet();
void recv_packet();
void statistics(int signo);
unsigned short cal_chksum(unsigned short *addr, int len);

int main(int argc, char *argv[])
{
    struct hostent *host;
    struct protoent *protocol;

    if (argc < 2) {
        cerr << "usage: " << argv[0] << " <hostname>" << endl;
        return 1;
    }

    if ((protocol = getprotobyname("icmp")) == NULL) {
        cerr << "getprotobyname() error" << endl;
        return 1;
    }

    if ((sockfd = socket(AF_INET, SOCK_RAW, protocol->p_proto)) < 0) {
        cerr << "socket() error" << endl;
        return 1;
    }

    pid = getpid();
    memset(&dest_addr, 0, sizeof(dest_addr));
    dest_addr.sin_family = AF_INET;

    if ((host = gethostbyname(argv[1])) == NULL) {
        cerr << "gethostbyname() error" << endl;
        return 1;
    }

    memcpy(&dest_addr.sin_addr, host->h_addr, host->h_length);
    printf("PING %s (%s) %d bytes of data.\n", argv[1], inet_ntoa(dest_addr.sin_addr), datalen);

    memset(sendpacket, 0, sizeof(sendpacket));
    memset(recvpacket, 0, sizeof(recvpacket));

    signal(SIGALRM, statistics);

    while (nsend < MAX_NO_PACKETS) {
        nsend++;

        send_packet();
        recv_packet();
        sleep(1);
    }

    close(sockfd);
    return 0;
}

void send_packet()
{
    int len;
    struct timeval tv;

    gettimeofday(&tvsend, NULL);
    memcpy(sendpacket, &tvsend, sizeof(tvsend));
    len = datalen + sizeof(tvsend);
    sendto(sockfd, sendpacket, len, 0, (struct sockaddr *)&dest_addr, sizeof(dest_addr));
}

void recv_packet()
{
    int n, fromlen;
    extern int errno;

    signal(SIGALRM, statistics);

    fromlen = sizeof(from_addr);

    while (1) {
        alarm(MAX_WAIT_TIME);

        if ((n = recvfrom(sockfd, recvpacket, sizeof(recvpacket), 0, (struct sockaddr *)&from_addr, &fromlen)) < 0) {
            if (errno == EINTR) {
                cerr << "recvfrom() timeout" << endl;
                return;
            }

            cerr << "recvfrom() error" << endl;
            return;
        }

        gettimeofday(&tvrecv, NULL);
        nreceived++;

        if (n < datalen + sizeof(tvsend)) {
            cerr << "received packet size is less than data length + sizeof(timeval)" << endl;
            continue;
        }

        struct timeval *tvsend = (struct timeval *)recvpacket;
        struct timeval *tvrecv = (struct timeval *)(recvpacket + sizeof(struct timeval));
        struct timeval tvresult;

        timersub(tvrecv, tvsend, &tvresult);

        printf("%d bytes from %s: icmp_seq=%u ttl=%d time=%.3f ms\n", n, inet_ntoa(from_addr.sin_addr), nreceived, from_addr.sin_ttl, tvresult.tv_sec * 1000.0 + tvresult.tv_usec / 1000.0);
    }
}

void statistics(int signo)
{
    printf("\n--- %s ping statistics ---\n", inet_ntoa(dest_addr.sin_addr));
    printf("%d packets transmitted, %d received, %%%d lost\n", nsend, nreceived, (nsend - nreceived) / nsend * 100);
    exit(0);
}

unsigned short cal_chksum(unsigned short *addr, int len)
{
    int nleft = len;
    int sum = 0;
    unsigned short *w = addr;
    unsigned short answer = 0;

    while (nleft > 1) {
        sum += *w++;
        nleft -= 2;
    }

    if (nleft == 1) {
        *(unsigned char *)(&answer) = *(unsigned char *)w;
        sum += answer;
    }

    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);
    answer = ~sum;

    return answer;
}

该程序使用 ICMP 协议实现 ping 命令的功能。具体实现方式为发送一个 ICMP 报文（包含时间戳），等待接收一个 ICMP 报文并计算收到报文的时间与发送报文的时间的差值。程序默认发送 3 个 ICMP 报文，最长等待时间为 5 秒。程序运行后输出每个接收到的 ICMP 报文的信息，包括 IP 地址、TTL、收到报文的时间与发送报文的时间的差值。