同步时间服务怎么写代码

同步时间服务可以使用网络时间协议(NTP)来实现。在C语言中，可以使用ntpdate库来获取网络时间。以下是一个简单的示例代码：

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

#define NTP_TIMESTAMP_DELTA 2208988800ull

int main(int argc, char* argv[])
{
int sockfd, n;
char* hostname = "pool.ntp.org";
char buf[1024];
struct sockaddr_in servaddr;
struct timeval tv;
uint64_t ntp_time;

sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);

memset(&servaddr, 0, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(123);
inet_pton(AF_INET, hostname, &servaddr.sin_addr);

memset(buf, 0, sizeof(buf));
buf[0] = 0x1b;

sendto(sockfd, buf, sizeof(buf), 0, (struct sockaddr*)&servaddr, sizeof(servaddr));

memset(buf, 0, sizeof(buf));
n = recvfrom(sockfd, buf, sizeof(buf), 0, NULL, NULL);

if (n > 0) {
uint32_t* ptr = (uint32_t*)&buf[40];
uint32_t high_word = ntohl(*ptr);
uint32_t low_word = ntohl(*(ptr + 1));
uint64_t ntp_time = ((uint64_t)high_word << 32) | low_word;
ntp_time -= NTP_TIMESTAMP_DELTA;
tv.tv_sec = ntp_time;
tv.tv_usec = 0;
settimeofday(&tv, NULL);
}

close(sockfd);

return 0;
}