Boost C++ date_time microsec_clock and second_clock

Question

I discovered a strange result in Boost C++ date time library. There is inconsistency between microsec_clock and second_clock, and I don't understand why is that. I am using Windows XP 32-bits

My snip of code:

using namespace boost::posix_time;
...
ptime now = second_clock::universal_time();
std::cout << "Current Time is: "<< to_iso_extended_string(now)<< std::endl;
ptime now_2 = microsec_clock::universal_time();
std::cout << "Current Time is: "<< to_iso_extended_string(now_2)<< std::endl;
...

The print-out I expected are current time without miliseconds and with milliseonds. However, what I have in my pc is:

2009-10-14T16:07:38  
1970-06-24T20:36:09.375890

I don't understand why there is a weired date (year 1970???) in my microsec_clock time. Related documentation for Boost: link to boost date time

Answer 1

Not sure what could be wrong for you; the exact same code works for me.

$ cat > test.cc
#include <boost/date_time/gregorian/gregorian.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
using namespace boost::posix_time;
int main() {
    ptime now = second_clock::universal_time();
    std::cout << "Current Time is: "<< to_iso_extended_string(now)<< std::endl;
    ptime now_2 = microsec_clock::universal_time();
    std::cout << "Current Time is: "<< to_iso_extended_string(now_2)<< std::endl;
    return 0;
}
^D
$ c++ -lboost_date_time test.cc
$ ./a.out
Current Time is: 2009-10-14T16:26:55
Current Time is: 2009-10-14T16:26:55.586295

Implementation-wise, second_clock uses time and microsec_clock uses gettimeofday or GetSystemTimeAsFileTime underneath, depending on the platform. Something appears wrong with your platform -- what is your OS and version?

---

What is your Boost version? If it is 1.38 or lower, upgrade to 1.39 or apply the fix to #2809 manually.

--- boost/date_time/filetime_functions.hpp  (revision 53621)
+++ boost/date_time/filetime_functions.hpp  (revision 53622)
@@ -96,9 +96,7 @@
     {
         /* shift is difference between 1970-Jan-01 & 1601-Jan-01
         * in 100-nanosecond intervals */
-        const uint64_t c1 = 27111902UL;
-        const uint64_t c2 = 3577643008UL; // issues warning without 'UL'
-        const uint64_t shift = (c1 << 32) + c2;
+        const uint64_t shift = 116444736000000000ULL; // (27111902 << 32) + 3577643008

         union {
             FileTimeT as_file_time;

Windows FileTime has a different offset from UNIX time, and the code that was in Boost before would not generate the correct offset difference in certain optimizing compilers.

Answer 2

The 1970 date most likely comes from the way unix time is represented, as seconds from January 1 1970. I would guess that maybe it is somehow getting the system uptime in milliseconds and interpreting it as seconds since 1/1/1970. An uptime of a little over 4 hours would come up with this date.

Answer 3

Unlike second_clock, the microsec_clock::universal_time documentation mentions: Returns the UTC time based on computer settings.
You should check your hardware clock settings (or where-ever microsec gets its values from).

edit:
If its not related to your computers settings it would have to be an misbehaviour in boost, which i highly doubt.