Re: [Boost-users] [Chrono] Negative real time

Le 22/05/12 18:55, Wilfried Kirschenmann a écrit :

Dear chrono maintainer team,

Using the following example :

int main(int argc, char **argv) { boost::chrono::process_real_cpu_clock::time_point start = boost::chrono::process_real_cpu_clock::now();

for ( long i = 0; i < 1000; ++i ) std::sqrt( 123.456L ); // burn some time Sleep(10000); //idle some time

boost::chrono::process_real_cpu_clock::time_point end = boost::chrono::process_real_cpu_clock::now(); std::cout << end << std::endl;

boost::chrono::process_real_cpu_clock::duration elapsed = (end - start); std::cout << "took real : " << elapsed << "nanoseconds\n";

return 0; }

I obtain negative times.

I run boost 1.49 win32 on Windows 7 x64 with Visual studio 2010.

Studying the behavior of the timer, I think that the error is one of these : - process_real_cpu_clock::now() only stores the current time in a 32 bit integer instead of a 64 bit integer

I don't know from where are you getting this conclusion. process_real_cpu_clock is using boost::int_least64_t, as representation. typedef duration nanoseconds; // at least 64 bits needed class BOOST_CHRONO_DECL process_real_cpu_clock { public: typedef nanoseconds duration; typedef duration::rep rep; typedef duration::period period; typedef chrono::time_point time_point; BOOST_STATIC_CONSTEXPR bool is_steady = true; static BOOST_CHRONO_INLINE time_point now() BOOST_NOEXCEPT; #if !defined BOOST_CHRONO_DONT_PROVIDE_HYBRID_ERROR_HANDLING static BOOST_CHRONO_INLINE time_point now(system::error_code & ec ); #endif };

- time_points only prints the 32 lowest bits. I came to this conclusion by observing the results printed before they got negatives (printing in the loop with the sqrt): 2019000000 tel:2019000000 nanoseconds is the last value printed before getting negative.

I guess that you have included chrono_io.hpp. Could you confim this? If not, you will need to get the number of nanoseconds using count() std::cout << "took real : " << elapsed.count() << "nanoseconds\n"; If you have included it, the output should contain nanoseconds twice. E.g. 2383000 nanoseconds since process start-up took real : 37000 nanosecondsnanoseconds

Is there any mistake in my way of using this chronometer ?

It depends of whether you have included chrono_io.hpp or not. If not, could you post the complete program? HTH, Vicente