我正在制作一个需要与远程NTP服务器同步系统时钟的C++软件。目前，我使用"system"命令来调用控制台"ntpdate"命令。
但我认为这是一种丑陋的方式。
你知道有哪些库可以让我连接到远程NTP服务器吗？谢谢。
2个回答
8
这段代码可以在c++中使用（改编自c语言）。它将从pool.ntp.br获取协调世界时UTC时间（必须使用IP）。如果你能找到如何获取DAYTIME（夏令时- horario verao），请告知。我可以从UFRJ pads服务器获取，但由于他们一年大部分时间都在罢工，所以不可靠。
/* This code will query a ntp server for the local time and display
* it. it is intended to show how to use a NTP server as a time
* source for a simple network connected device.
* This is the C version. The orignal was in Perl
*
* For better clock management see the offical NTP info at:
* http://www.eecis.udel.edu/~ntp/
*
* written by Tim Hogard (thogard@abnormal.com)
* Thu Sep 26 13:35:41 EAST 2002
* Converted to C Fri Feb 21 21:42:49 EAST 2003
* this code is in the public domain.
* it can be found here http://www.abnormal.com/~thogard/ntp/
*
*/
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <time.h>
#include <string.h>
#include <iostream>
void ntpdate();
int main() {
ntpdate();
return 0;
}
void ntpdate() {
//char *hostname=(char *)"163.117.202.33";
//char *hostname=(char *)"pool.ntp.br";
char *hostname=(char *)"200.20.186.76";
int portno=123; //NTP is port 123
int maxlen=1024; //check our buffers
int i; // misc var i
unsigned char msg[48]={010,0,0,0,0,0,0,0,0}; // the packet we send
unsigned long buf[maxlen]; // the buffer we get back
//struct in_addr ipaddr; //
struct protoent *proto; //
struct sockaddr_in server_addr;
int s; // socket
long tmit; // the time -- This is a time_t sort of
//use Socket;
//
//#we use the system call to open a UDP socket
//socket(SOCKET, PF_INET, SOCK_DGRAM, getprotobyname("udp")) or die "socket: $!";
proto=getprotobyname("udp");
s=socket(PF_INET, SOCK_DGRAM, proto->p_proto);
perror("socket");
//
//#convert hostname to ipaddress if needed
//$ipaddr = inet_aton($HOSTNAME);
memset( &server_addr, 0, sizeof( server_addr ));
server_addr.sin_family=AF_INET;
server_addr.sin_addr.s_addr = inet_addr(hostname);
//argv[1] );
//i = inet_aton(hostname,&server_addr.sin_addr);
server_addr.sin_port=htons(portno);
//printf("ipaddr (in hex): %x\n",server_addr.sin_addr);
/*
* build a message. Our message is all zeros except for a one in the
* protocol version field
* msg[] in binary is 00 001 000 00000000
* it should be a total of 48 bytes long
*/
// send the data
printf("sending data..\n");
i=sendto(s,msg,sizeof(msg),0,(struct sockaddr *)&server_addr,sizeof(server_addr));
perror("sendto");
// get the data back
struct sockaddr saddr;
socklen_t saddr_l = sizeof (saddr);
i=recvfrom(s,buf,48,0,&saddr,&saddr_l);
perror("recvfr:");
//We get 12 long words back in Network order
/*
for(i=0;i<12;i++) {
//printf("%d\t%-8x\n",i,ntohl(buf[i]));
long tmit2=ntohl((time_t)buf[i]);
std::cout << "Round number " << i << " time is " << ctime(&tmit2) << std::endl;
}
*/
/*
* The high word of transmit time is the 10th word we get back
* tmit is the time in seconds not accounting for network delays which
* should be way less than a second if this is a local NTP server
*/
//tmit=ntohl((time_t)buf[10]); //# get transmit time
tmit=ntohl((time_t)buf[4]); //# get transmit time
//printf("tmit=%d\n",tmit);
/*
* Convert time to unix standard time NTP is number of seconds since 0000
* UT on 1 January 1900 unix time is seconds since 0000 UT on 1 January
* 1970 There has been a trend to add a 2 leap seconds every 3 years.
* Leap seconds are only an issue the last second of the month in June and
* December if you don't try to set the clock then it can be ignored but
* this is importaint to people who coordinate times with GPS clock sources.
*/
tmit-= 2208988800U;
//printf("tmit=%d\n",tmit);
/* use unix library function to show me the local time (it takes care
* of timezone issues for both north and south of the equator and places
* that do Summer time/ Daylight savings time.
*/
//#compare to system time
//printf("Time: %s",ctime(&tmit));
std::cout << "time is " << ctime(&tmit) << std::endl;
i=time(0);
//printf("%d-%d=%d\n",i,tmit,i-tmit);
//printf("System time is %d seconds off\n",(i-tmit));
std::cout << "System time is " << (i-tmit) << " seconds off" << std::endl;
}
- tony gil
1
6
您是否考虑在该系统上运行ntpd以确保时钟正确，而不是让您的软件手动发出同步命令，并可能导致其他应用程序不喜欢突然的时间跳跃，尤其是向后。
话虽如此，我相信有libntp。
随着Google为我找到更多信息，我会添加更多内容。
- r_ahlskog
6
2+1 对于
ntpd 和短语 突然时间跳跃。回到未来！ - Li-aung Yip@Li-aungYip，是的，我手动使用ntpdate时，当文件来自未来时，我遇到了各种进程失败的情况。 - r_ahlskog
1我最有趣的一次（用户可见）经历是跳过时钟导致KDE的合成窗口管理器出现故障并死机。显然，
kwm使用自上一帧渲染以来的时间戳来跟踪其性能，目的是在事情变得太慢时关闭合成。将时钟向前跳10秒会使它认为只获得了0.1 FPS并触发kwm的崩溃。 ;) - Li-aung Yip听起来很有趣，也可能是解决问题的方法，也许需要试着去纠缠一些kwin开发者，告诉他们这是多么好的一个想法。不过他们只会告诉我去修复它并发送一个补丁，没有什么乐趣可言。 - r_ahlskog
是的，ntpd似乎是正确的选择：）。感谢您的建议和有趣的评论。 - César Ortiz
你可能想看一下Github上的ntpclient代码：https://github.com/lettier/ntpclient/blob/master/source/c/main.c
此外，还有相关文档可参考：https://lettier.github.io/posts/2016-04-26-lets-make-a-ntp-client-in-c.html - hmojtaba
网页内容由stack overflow 提供, 点击上面的可以查看英文原文，
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原文链接
ntpd守护进程，它可以始终同步您系统的时钟。 - Li-aung Yip