Re: [Boost-users] [boost][chrono] time_since_epoch different on windows and linux

Subject: Re: [Boost-users] [boost][chrono] time_since_epoch different on windows and linux
From: Ralf Globisch (RGlobisch_at_[hidden])
Date: 2011-12-09 00:21:06

>>> On 09/12/2011 at 00:20, in message <4EE13819.20403_at_[hidden]>,
"Vicente J.
Botet Escriba" <vicente.botet_at_[hidden]> wrote:
> Le 08/12/11 19:09, Ralf Globisch a écrit :
>> Hi,
>>
>> I've run into a bit of a funny one and I'm not sure if I'm missing
>> something or whether I've encountered a bug.
>>
>> The following code excerpt *seems* to have 2 different results on
>> windows 7 (VS2010) and linux (gcc4.6) using boost version 1.47.
>>
>> #include<iostream>
>> #include<cstdint>
>> #include<boost/chrono.hpp>
>>
>> int main(int argc, char** argv)
>> {
>>    boost::chrono::duration<double>  sec =
>>    boost::chrono::system_clock::now().time_since_epoch();
>>    uint32_t uiSeconds = sec.count();
>>    double dMinutes = uiSeconds/60.0;
>>    double dHours = dMinutes/60.0;
>>    double dDays = dHours/24.0;
>>    double dYears = dDays/365.0;
>>
>>    std::cout<<  "Sec: "<<  uiSeconds<<
>>                " Min: "<<  dMinutes<<
>>                " Hours: "<<  dHours<<
>>                " Days: "<<  dDays<<
>>                " Years: "<<  dYears<<  std::endl;
>>
>>    return 0;
>> }
>>
>>
>> This outputs the following:
>> Linux:
>>   Sec: 1323362917 Min: 2.2056e+07 Hours: 367601 Days: 15316.7 Years:
41.9636
>>
>> Windows:
>>   Sec: 82934819 Min: 1.38225e+006 Hours: 23037.4 Days: 959.894
Years: 
> 2.62985
>>
>> The linux results is the expected result: 1970 + 41 years = ~2011.
>> Why does the windows result differ? I've run the windows version
>> on two different windows machines with the same result.
>>
>> Am I using the library incorrectly? I'm trying to obtain seconds
since 1970
>> so that I can from there calculate seconds since 1900 to calculate
>> an NTP timestamp.
>>
>> Thanks for any help/suggestions!
> Hi,
> 
> time_since_epoch() gives the time since an undetermined epoch. I will
use 
> instead
> boost::chrono:time_system_clock::to_time_t which gives you the number
of 
> nanoseconds since 1970.
> 
>    std::time_t sec =
>      boost::chrono:time_system_clock::to_time_t(
>       boost::chrono::system_clock::now().time_since_epoch()
>      );
> 
> 
> Hth,
> Vicente
> 
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden] 
> http://lists.boost.org/mailman/listinfo.cgi/boost-users 

Have verified that I get the correct time now.
Just a minor correction in case someone  
stumbles on this thread and fails to compile:

It should be 
std::time_t sec =
     boost::chrono:system_clock::to_time_t(
      boost::chrono::system_clock::now()
     );

Thanks for writing and maintaining this wonderful library Vicente.

Regards,
Ralf

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