How to set system time in Unix C or C++

Posted on 2002-04-23
Last Modified: 2013-12-26
I am connected to a server (actually the NYSE) that transmits a multicast time stamp every 10 seconds or so. I can receive and decode the time stamp easily, as its in text format yymmddhhmmss. How do I programaticly  (in c or c++) get the system time in the same format and set the system time if its more than a second off.

I am running c and/or c++ on a sun solaris box.

Austin <>
Question by:AustinKalb
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LVL 38

Expert Comment

ID: 6964716
use the system() function.


   char ctime(25)="date +%Y%m%d%H%M%S"

   and use: system(ctime), to get the time in the format you wanted.

Author Comment

ID: 6964729
how do i get the system time to compare? i need the hours and sec in integer format.
LVL 38

Expert Comment

ID: 6964865
if you only need hours and sec:

   for hours:
   date +%H
   for sec:
   use date +%S

   and put them into system().

   for minutes:
   use date +%M

   do a "man date" to find out more details on your system.
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Expert Comment

ID: 6964931
sidenote: Only root can change the system time. So either set the s-bit (owner root) or execute/schedule(crontab) the program as root

Author Comment

ID: 6965668
I was needing to "retreive" the system time as well, so I can compare it to the time I received from the NYSE. How do I get the system time into some int variables (int hh,mm,ss).

LVL 86

Expert Comment

ID: 6965715
Use gettimeofday()/settimeofday()

       gettimeofday, settimeofday - get / set time

       #include <sys/time.h>
       #include <unistd.h>

       int gettimeofday(struct timeval *tv, struct timezone *tz);
       int settimeofday(const struct timeval *tv ,  const  struct
       timezone *tz);


Accepted Solution

ecw earned 100 total points
ID: 6965747
I suggest you convert the time you get from NYSE to a time_t, get the system time using time(2), and compare them.  Pull apart NYSE's yymmddhhmmss format, and stuff it into a struct tm, use mktime to turn it into a time_t, then compare.

Author Comment

ID: 7006932
turns out their time broadcast wasnt that good.. I didnt end up using it!

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