是否有任何C/C++庫與遠程NTP服務器連接？

Question

我正在製作一個需要將系統時鐘與遠程NTP服務器同步的C++軟件。 現在，我正在使用「system」命令來調用控制檯「ntpdate」命令。

..但我認爲這是一個醜陋的方式來做到這一點。

你知道任何庫讓我連接到遠程NTP服務器嗎？ 謝謝。

Answer 1

如果在系統上運行ntpd以確保時鐘正確，而不是讓軟件手動發出同步，並且可能導致其他應用程序不能享受突然的時間跳轉（尤其是後退），可能會導致問題，這不是一個更好的解決方案。

這就是說有libntp我相信。

Google會爲我找到更多的東西。

Answer 2

這個工作在C++（改編自c）。它會從pool.ntp.br得到你的UTC時間（你必須使用IP）。如果您設法弄清楚如何獲得DAYTIME（夏令時 - horario verao），請告知。我可以從UFRJ墊服務器得到它，但UFRJ是不可靠的，有什麼和他們在一起罷工半年...

/* 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; 
}