c语言实现ping命令

实现ping命令需要使用系统底层的网络API，这里给出一个基于Linux系统的C语言实现示例：

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

#define PACKET_SIZE 4096  
#define MAX_WAIT_TIME   5  
#define MAX_NO_PACKETS  4  

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

unsigned short cal_chksum(unsigned short *addr, int len)  
{  
    int sum = 0;  
    unsigned short res = 0;  
    while(len > 1)  
    {  
        sum += *addr++;  
        len -= 2;  
    }  
    if(len == 1)  
    {  
        *((unsigned char *)(&res)) = *((unsigned char *)addr);  
        sum += res;  
    }  
    sum = (sum >> 16) + (sum & 0xffff);  
    sum += (sum >> 16);  
    res = ~sum;  
    return res;  
}  

int pack(int pack_no)  
{  
    int i, packsize;  
    struct icmp *icmp;  
    struct timeval *tval;  
    icmp = (struct icmp*)sendpacket;  
    icmp->icmp_type = ICMP_ECHO;  
    icmp->icmp_code = 0;  
    icmp->icmp_cksum = 0;  
    icmp->icmp_seq = pack_no;  
    icmp->icmp_id = getpid();  
    packsize = 8 + datalen;  
    tval = (struct timeval *)icmp->icmp_data;  
    gettimeofday(tval, NULL);  
    icmp->icmp_cksum = cal_chksum((unsigned short *)icmp, packsize);  
    return packsize;  
}  

int unpack(char *buf, int len)  
{  
    int i, iphdrlen;  
    struct ip *ip;  
    struct icmp *icmp;  
    struct timeval *tvsend;  
    double rtt;  
    ip = (struct ip *)buf;  
    iphdrlen = ip->ip_hl << 2;  
    icmp = (struct icmp *)(buf + iphdrlen);  
    len -= iphdrlen;  
    if(len < 8)  
    {  
        printf("ICMP packets\'s length is less than 8\n");  
        return -1;  
    }  
    if((icmp->icmp_type == ICMP_ECHOREPLY) && (icmp->icmp_id == getpid()))  
    {  
        tvsend = (struct timeval *)icmp->icmp_data;  
        gettimeofday(&tvrecv, NULL);  
        tv_sub(&tvrecv, tvsend);  
        rtt = tvrecv.tv_sec * 1000 + tvrecv.tv_usec / 1000.0;  
        printf("%d byte from %s: icmp_seq=%u ttl=%d rtt=%.3f ms\n",  
            len, inet_ntoa(from.sin_addr), icmp->icmp_seq, ip->ip_ttl, rtt);  
        return 0;  
    }  
    else  
    {  
        return -1;  
    }  
}  

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;  
}  

void ping()  
{  
    int i, packsize;  
    struct timeval tv;  
    tv.tv_sec = MAX_WAIT_TIME;  
    tv.tv_usec = 0;  
    for (i = 0; i < MAX_NO_PACKETS; i++)  
    {  
        nsend++;  
        packsize = pack(nsend);  
        if (sendto(sockfd, sendpacket, packsize, 0, (struct sockaddr *)&dest_addr, sizeof(dest_addr)) < 0)  
        {  
            printf("sendto error: %s\n", strerror(errno));  
            continue;  
        }  
        if (recvfrom(sockfd, recvpacket, sizeof(recvpacket), 0, (struct sockaddr *)&from, (socklen_t *)&fromlen) < 0)  
        {  
            printf("recvfrom error: %s\n", strerror(errno));  
            continue;  
        }  
        if (unpack(recvpacket, sizeof(recvpacket)) == -1)  
        {  
            printf("unpack error\n");  
            continue;  
        }  
        nreceived++;  
        usleep(1000000);  
    }  
}  

int main(int argc, char *argv[])  
{  
    struct hostent *host;  
    struct protoent *protocol;  
    char protoname[] = "icmp";  
    int size = 50 * 1024;  
    if (argc < 2)  
    {  
        printf("usage: ping hostname/IP address\n");  
        return 0;  
    }  
    if ((protocol = getprotobyname(protoname)) == NULL)  
    {  
        printf("getprotobyname() error\n");  
        return 0;  
    }  
    if ((sockfd = socket(AF_INET, SOCK_RAW, protocol->p_proto)) < 0)  
    {  
        printf("socket() error\n");  
        return 0;  
    }  
    setuid(getuid());  
    setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &size, sizeof(size));  
    bzero(&dest_addr, sizeof(dest_addr));  
    dest_addr.sin_family = AF_INET;  
    if ((dest_addr.sin_addr.s_addr = inet_addr(argv[1])) == INADDR_NONE)  
    {  
        if ((host = gethostbyname(argv[1])) == NULL)  
        {  
            printf("gethostbyname() error\n");  
            return 0;  
        }  
        memcpy((char *)&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);  
    ping();  
    printf("--- %s ping statistics ---\n", argv[1]);  
    printf("%d packets transmitted, %d received, %%%.2f packet loss\n",  
        nsend, nreceived, (nsend - nreceived) * 100.0 / nsend);  
    close(sockfd);  
    return 0;  
}  

这个实现使用了ICMP协议来模拟ping命令。需要注意的是，这个实现中使用了系统底层的网络API，因此需要在Linux系统下编译运行。如果需要在其他系统上运行，请根据具体系统的网络API进行调整。