用c语言实现ping命令

以下是使用C语言实现ping命令的示例代码：

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

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

char sendpacket[PACKET_SIZE];
char recvpacket[PACKET_SIZE];
int sockfd, datalen = 56;
int nsend = 0, nreceived = 0;
struct sockaddr_in dest_addr;
struct timeval tvrecv;

unsigned short cal_chksum(unsigned short *addr, int len);

void tv_sub(struct timeval *out, struct timeval *in) {
    if ((out->tv_usec -= in->tv_usec) < 0) {
        --out->tv_sec;
        out->tv_usec += 1000000;
    }
    out->tv_sec -= in->tv_sec;
}

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;
}

void send_packet() {
    int packetsize;
    struct icmp *icmp;
    icmp = (struct icmp*) sendpacket;
    icmp->icmp_type = ICMP_ECHO;
    icmp->icmp_code = 0;
    icmp->icmp_cksum = 0;
    icmp->icmp_seq = nsend++;
    icmp->icmp_id = getpid();
    packetsize = 8 + datalen;
    gettimeofday((struct timeval*) icmp->icmp_data, NULL);
    icmp->icmp_cksum = cal_chksum((unsigned short *) icmp, packetsize);
    sendto(sockfd, sendpacket, packetsize, 0, (struct sockaddr*) &dest_addr, sizeof(dest_addr));
}

void recv_packet() {
    int n, fromlen;
    extern int errno;
    fromlen = sizeof(struct sockaddr_in);

    while (1) {
        fd_set rfds;
        FD_ZERO(&rfds);
        FD_SET(sockfd, &rfds);
        struct timeval timeout;
        timeout.tv_sec = MAX_WAIT_TIME;
        timeout.tv_usec = 0;
        int retval = select(sockfd + 1, &rfds, NULL, NULL, &timeout);

        if (retval == -1) {
            printf("select error\n");
            break;
        } else if (retval == 0) {
            printf("request timeout.\n");
            break;
        } else {
            n = recvfrom(sockfd, recvpacket, sizeof(recvpacket), 0, (struct sockaddr*) &dest_addr, &fromlen);

            if (n < 0) {
                if (errno == EINTR)
                    continue;

                printf("recvfrom error\n");
                break;
            }

            gettimeofday(&tvrecv, NULL);
            struct ip *ip;
            struct icmp *icmp;
            ip = (struct ip*) recvpacket;
            icmp = (struct icmp*) (recvpacket + (ip->ip_hl << 2));
            int icmplen = n - (ip->ip_hl << 2);

            if (icmp->icmp_type == ICMP_ECHOREPLY) {
                if (icmp->icmp_id != getpid())
                    continue;

                if (icmplen < 8)
                    continue;

                if (icmp->icmp_seq != nreceived)
                    continue;

                nreceived++;
                printf("%d bytes from %s: icmp_seq=%u ttl=%d time=%ld ms\n", icmplen, inet_ntoa(dest_addr.sin_addr), icmp->icmp_seq, ip->ip_ttl, (tvrecv.tv_sec - ((struct timeval*) icmp->icmp_data)->tv_sec) * 1000 + (tvrecv.tv_usec - ((struct timeval*) icmp->icmp_data)->tv_usec) / 1000);
            } else {
                continue;
            }
        }
    }
}

void ping() {
    struct hostent *host;
    struct protoent *protocol;

    if ((protocol = getprotobyname("icmp")) == NULL) {
        printf("getprotobyname error\n");
        exit(1);
    }

    if ((sockfd = socket(AF_INET, SOCK_RAW, protocol->p_proto)) < 0) {
        printf("socket error\n");
        exit(1);
    }

    if ((host = gethostbyname("localhost")) == NULL) {
        printf("gethostbyname error\n");
        exit(1);
    }

    memset(&dest_addr, 0, sizeof(dest_addr));
    dest_addr.sin_family = AF_INET;
    dest_addr.sin_addr = *((struct in_addr*) host->h_addr);

    printf("PING %s (%s): %d data bytes\n", host->h_name, inet_ntoa(dest_addr.sin_addr), datalen);
    send_packet();
    recv_packet();
    close(sockfd);
}

int main(int argc, char **argv) {
    ping();
    return 0;
}

注意：该示例代码只实现了基本的ping功能，没有实现ping命令的全部参数和功能。如果需要实现更完整的ping命令，请参考相关文档或代码库。