c语言实现sntp
时间: 2023-07-13 18:25:49 浏览: 102
SNTP(Simple Network Time Protocol)是一种简单的网络时间协议,用于同步计算机系统时间。下面是一个使用C语言实现SNTP的示例代码:
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define NTP_SERVER "pool.ntp.org"
#define NTP_PORT 123
#define NTP_PACKET_SIZE 48
#define NTP_TIMESTAMP_OFFSET 2208988800UL
typedef struct
{
uint8_t li_vn_mode; // Leap indicator, Version, Mode
uint8_t stratum; // Stratum level
uint8_t poll; // Poll interval
uint8_t precision; // Precision
uint32_t rootDelay; // Root delay between local machine and server
uint32_t rootDispersion; // Root dispersion (maximum error)
uint32_t refId; // Reference clock identifier
uint32_t refTm_s; // Reference time-stamp seconds
uint32_t refTm_f; // Reference time-stamp fraction of a second
uint32_t origTm_s; // Originate time-stamp seconds
uint32_t origTm_f; // Originate time-stamp fraction of a second
uint32_t rxTm_s; // Received time-stamp seconds
uint32_t rxTm_f; // Received time-stamp fraction of a second
uint32_t txTm_s; // Transmit time-stamp seconds
uint32_t txTm_f; // Transmit time-stamp fraction of a second
} ntp_packet;
int main()
{
int sockfd, n;
char buffer[NTP_PACKET_SIZE];
struct sockaddr_in servaddr;
ntp_packet *ntp_pkt = (ntp_packet *)buffer;
// Create UDP socket
sockfd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (sockfd < 0) {
perror("socket creation failed");
exit(EXIT_FAILURE);
}
// Set server address and port
memset(&servaddr, 0, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(NTP_PORT);
if (inet_pton(AF_INET, NTP_SERVER, &servaddr.sin_addr) <= 0) {
perror("inet_pton failed");
exit(EXIT_FAILURE);
}
// Initialize NTP packet
memset(buffer, 0, NTP_PACKET_SIZE);
ntp_pkt->li_vn_mode = 0x1b; // LI = 0, VN = 3, Mode = 3 (client)
ntp_pkt->txTm_s = htonl(NTP_TIMESTAMP_OFFSET + time(NULL));
// Send NTP request to server
n = sendto(sockfd, buffer, NTP_PACKET_SIZE, 0, (const struct sockaddr *)&servaddr, sizeof(servaddr));
if (n < 0) {
perror("sendto failed");
exit(EXIT_FAILURE);
}
// Receive NTP response from server
n = recv(sockfd, buffer, NTP_PACKET_SIZE, 0);
if (n < 0) {
perror("recv failed");
exit(EXIT_FAILURE);
}
// Extract NTP timestamp from response
time_t ntp_time = ntohl(ntp_pkt->rxTm_s) - NTP_TIMESTAMP_OFFSET;
// Set system time to NTP timestamp
struct timeval tv = { .tv_sec = ntp_time };
if (settimeofday(&tv, NULL) < 0) {
perror("settimeofday failed");
exit(EXIT_FAILURE);
}
printf("System time set to: %s", ctime(&ntp_time));
close(sockfd);
return 0;
}
```
该代码使用了标准的C库函数和POSIX网络编程API来实现SNTP客户端,基本思路如下:
1. 使用`socket()`创建UDP套接字。
2. 设置NTP服务器的地址和端口,并将NTP请求数据包打包成一个`ntp_packet`结构体。
3. 使用`sendto()`将NTP请求数据包发送到NTP服务器。
4. 使用`recv()`从NTP服务器接收NTP响应数据包。
5. 从NTP响应数据包中提取NTP时间戳。
6. 使用`settimeofday()`将系统时间设置为NTP时间戳。
需要注意的是,NTP时间戳的计算方式是将1970年1月1日至NTP时间戳的秒数加上`NTP_TIMESTAMP_OFFSET`的值,因为NTP时间戳是从1900年1月1日开始计算的。