In my thread (using boost::thread) I need to retrieve the current time in ms or less and to convert into ms:
Actually, reading here I've found this:
tick = boost::posix_time::second_clock::local_time();
now = boost::posix_time::second_clock::local_time();
And seems to work, but after I need to have a long value of the milliseconds of the now...
How can I do it?
You can use boost::posix_time::time_duration to get the time range. E.g like this
boost::posix_time::time_duration diff = tick - now;
diff.total_milliseconds();
And to get a higher resolution you can change the clock you are using. For example to the boost::posix_time::microsec_clock, though this can be OS dependent. On Windows, for example, boost::posix_time::microsecond_clock has milisecond resolution, not microsecond.
An example which is a little dependent on the hardware.
int main(int argc, char* argv[])
{
boost::posix_time::ptime t1 = boost::posix_time::second_clock::local_time();
boost::this_thread::sleep(boost::posix_time::millisec(500));
boost::posix_time::ptime t2 = boost::posix_time::second_clock::local_time();
boost::posix_time::time_duration diff = t2 - t1;
std::cout << diff.total_milliseconds() << std::endl;
boost::posix_time::ptime mst1 = boost::posix_time::microsec_clock::local_time();
boost::this_thread::sleep(boost::posix_time::millisec(500));
boost::posix_time::ptime mst2 = boost::posix_time::microsec_clock::local_time();
boost::posix_time::time_duration msdiff = mst2 - mst1;
std::cout << msdiff.total_milliseconds() << std::endl;
return 0;
}
On my win7 machine. The first out is either 0 or 1000. Second resolution.
The second one is nearly always 500, because of the higher resolution of the clock. I hope that help a little.
If you mean milliseconds since epoch you could do
ptime time_t_epoch(date(1970,1,1));
ptime now = microsec_clock::local_time();
time_duration diff = now - time_t_epoch;
x = diff.total_milliseconds();
However, it's not particularly clear what you're after.
Have a look at the example in the documentation for DateTime at Boost Date Time
// Get current date/time in milliseconds.
#include "boost/date_time/posix_time/posix_time.hpp"
namespace pt = boost::posix_time;
int main()
{
pt::ptime current_date_microseconds = pt::microsec_clock::local_time();
long milliseconds = current_date_microseconds.time_of_day().total_milliseconds();
pt::time_duration current_time_milliseconds = pt::milliseconds(milliseconds);
pt::ptime current_date_milliseconds(current_date_microseconds.date(),
current_time_milliseconds);
std::cout << "Microseconds: " << current_date_microseconds
<< " Milliseconds: " << current_date_milliseconds << std::endl;
// Microseconds: 2013-Jul-12 13:37:51.699548 Milliseconds: 2013-Jul-12 13:37:51.699000
}
Try this: import headers as mentioned.. gives seconds and milliseconds only. If you need to explain the code read this link.
#include <windows.h>
#include <stdio.h>
void main()
{
SYSTEMTIME st;
SYSTEMTIME lt;
GetSystemTime(&st);
// GetLocalTime(<);
printf("The system time is: %02d:%03d\n", st.wSecond, st.wMilliseconds);
// printf("The local time is: %02d:%03d\n", lt.wSecond, lt.wMilliseconds);
}
Related
I have been looking around to get what I want but I couldn't find anything hence my question (hopefully not a duplicate!)
I am looking to get a microsecond resolution epoch time (to be converted to a Date string) of the clock perhaps using chrono.
Following is what works for me for seconds resolution:
auto secondsEpochTime = std::chrono::duration_cast<std::chrono::seconds>(std::chrono::system_clock::now().time_since_epoch()).count();
std::cout << "Date string = " << ctime(&secondsEpochTime);
However when I change seconds to microseconds, ctime doesn't seem to reflect the correct date.
auto microSecondsEpochTime = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::system_clock::now().time_since_epoch()).count();
std::cout << "Date string = " << ctime(µSecondsEpochTime); // incorrect Date
Unfortunately std::chrono is not complete to provide a full answer to your question. You will have to use parts of the C library until C++23 at least otherwise you might end up with a race-prone implementation.
The idea is to get the timestamp and convert it to an integer as microseconds since epoch (1970-01-01).
Then use localtime_r to get the local time broken down in year/month/day/hour/minute/seconds and print it to string.
Finally append the milliseconds as an int padded to 3 digits and return the entire result as an std::string.
constexpr static int64_t ONEMICROSECOND = 1000000;
static std::string nowstr() {
auto now = std::chrono::system_clock::now();
auto onems = std::chrono::microseconds(1);
int64_t epochus = now.time_since_epoch()/onems;
time_t epoch = epochus/ONEMICROSECOND;
struct tm tms{};
localtime_r( &epoch, &tms );
char buf[128];
size_t nb = strftime( buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", &tms );
nb += ::sprintf( &buf[nb], ".%06d", int(epochus%ONEMICROSECOND) );
return std::string( buf, nb );
}
If you run this as-is it will likely return the timestamp in GMT. You will heave to set your timezone programatically if not set in the environment (as it happens with compiler explorer/Godbolt.
int main() {
setenv("TZ", "/usr/share/zoneinfo/America/New_York", 1);
std::cout << nowstr() << std::endl;
}
Results in
Program stdout
2022-10-01 22:51:03.988759
Compiler explorer link: https://godbolt.org/z/h88zhrr73
UPDATE: if you prefer to use boost::format (std::format is still incomplete on most compilers unfortunately) then you can do
static std::string nowstr() {
auto now = std::chrono::system_clock::now();
auto onems = std::chrono::microseconds(1);
int64_t epochus = now.time_since_epoch()/onems;
time_t epoch = epochus/ONEMICROSECOND;
struct tm tms{};
localtime_r( &epoch, &tms );
std::ostringstream ss;
ss << boost::format( "%04d-%02d-%02d %02d:%02d:%02d.%06d" )
% (tms.tm_year+1900) % (tms.tm_mon+1) % tms.tm_mday
% tms.tm_hour % tms.tm_min % tms.tm_sec
% (epochus%ONEMICROSECOND);
return ss.str();
}
You will have to use parts of the C library until C++23 at least
Umm... If your platform supports the full C++20 spec (at least with regards to format and chrono):
#include <chrono>
#include <format>
#include <iostream>
int
main()
{
auto tp = std::chrono::system_clock::now();
std::chrono::zoned_time zt{std::chrono::current_zone(),
std::chrono::time_point_cast<std::chrono::microseconds>(tp)};
std::cout << "Date string = " << std::format("{:%a %b %e %T %Y}", zt) << '\n';
}
Sample output:
Date string = Sat Oct 1 23:32:24.843844 2022
I want to measure elapsed time in seconds. With std::chrono::steady_clock I do it. However it suffers from system time changes.
Wasn't steady_clock supposed to not being affected by changes in system time?
How can I do that?
Here is the code:
#include <iostream>
#include <chrono>
#include <time.h>
std::chrono::steady_clock::time_point t = std::chrono::steady_clock::now();
/* Change system time */
std::time_t tnow = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());
tnow -= 20;
std::cout << "stime: " << stime(&tnow) << std::endl;
/********************************************************/
sleep(5);
std::chrono::steady_clock::time_point t2 = std::chrono::steady_clock::now();
std::cout << "ELAPSED: " << std::chrono::duration_cast<std::chrono::seconds>(t2-t).count() << std::endl;
This results:
stime: 0
ELAPSED: -15
What I wanted to get was:
ELAPSED: 5
Edit:
I have added C tag, because it seems that it is a kernel (or buildroot of board) bug. So, how could I achieve this without chrono? I mean, in a straight way (without having to watch system time changes).
How was the people living before chrono?
You can file a bug with your vendor.
From the standard:
Objects of class steady_clock represent clocks for which values of
time_point never decrease as physical time advances and for which
values of time_point advance at a steady rate relative to real
time. That is, the clock may not be adjusted.
If you can find a reliable source of monotonic time on your system, you can easily wrap that source in a custom chrono::clock and subsequently still make use of the type-safe chrono system. For example:
#include <chrono>
struct MyClock
{
using duration = std::chrono::nanoseconds;
using rep = duration::rep;
using period = duration::period;
using time_point = std::chrono::time_point<MyClock>;
static constexpr bool is_steady = true;
static time_point now() noexcept
{
using namespace std::chrono;
timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
return time_point{seconds{ts.tv_sec} + nanoseconds{ts.tv_nsec}};
}
};
Now you can say things like:
MyClock::time_point t = MyClock::now();
// ...
MyClock::time_point t2 = MyClock::now();
std::cout << "ELAPSED: " << std::chrono::duration_cast<std::chrono::seconds>(t2-t).count() << std::endl;
I have following C code:
uint64_t combine(uint32_t const sec, uint32_t const usec){
return (uint64_t) sec << 32 | usec;
};
uint64_t now3(){
struct timeval tv;
gettimeofday(&tv, NULL);
return combine((uint32_t) tv.tv_sec, (uint32_t) tv.tv_usec);
}
What this do it combine 32 bit timestamp, and 32 bit "something", probably micro/nanoseconds into single 64 bit integer.
I have really hard time to rewrite it with C++11 chrono.
This is what I did so far, but I think this is wrong way to do it.
auto tse = std::chrono::system_clock::now().time_since_epoch();
auto dur = std::chrono::duration_cast<std::chrono::nanoseconds>( tse ).count();
uint64_t time = static_cast<uint64_t>( dur );
Important note - I only care about first 32 bit to be "valid" timestamp.
Second 32 bit "part" can be anything - nano or microseconds - everything is good as long as two sequential calls of this function give me different second "part".
i want seconds in one int, milliseconds in another.
Here is code to do that:
#include <chrono>
#include <iostream>
int
main()
{
auto now = std::chrono::system_clock::now().time_since_epoch();
std::cout << now.count() << '\n';
auto s = std::chrono::duration_cast<std::chrono::seconds>(now);
now -= s;
auto ms = std::chrono::duration_cast<std::chrono::milliseconds>(now);
int si = s.count();
int msi = ms.count();
std::cout << si << '\n';
std::cout << msi << '\n';
}
This just output for me:
1447109182307707
1447109182
307
The C++11 chrono types use only one number to represent a time since a given Epoch, unlike the timeval (or timespec) structure which uses two numbers to precisely represent a time. So with C++11 chrono you don't need the combine() method.
The content of the timestamp returned by now() depends on the clock you use; there are tree clocks, described in http://en.cppreference.com/w/cpp/chrono :
system_clock wall clock time from the system-wide realtime clock
steady_clock monotonic clock that will never be adjusted
high_resolution_clock the clock with the shortest tick period available
If you want successive timestamps to be always different, use the steady clock:
auto t1 = std::chrono::steady_clock::now();
...
auto t2 = std::chrono::steady_clock::now();
assert (t2 > t1);
Edit: answer to comment
#include <iostream>
#include <chrono>
#include <cstdint>
int main()
{
typedef std::chrono::duration< uint32_t, std::ratio<1> > s32_t;
typedef std::chrono::duration< uint32_t, std::milli > ms32_t;
s32_t first_part;
ms32_t second_part;
auto t1 = std::chrono::nanoseconds( 2500000000 ); // 2.5 secs
first_part = std::chrono::duration_cast<s32_t>(t1);
second_part = std::chrono::duration_cast<ms32_t>(t1-first_part);
std::cout << "first part = " << first_part.count() << " s\n"
<< "seconds part = " << second_part.count() << " ms" << std::endl;
auto t2 = std::chrono::nanoseconds( 2800000000 ); // 2.8 secs
first_part = std::chrono::duration_cast<s32_t>(t2);
second_part = std::chrono::duration_cast<ms32_t>(t2-first_part);
std::cout << "first part = " << first_part.count() << " s\n"
<< "seconds part = " << second_part.count() << " ms" << std::endl;
}
Output:
first part = 2 s
seconds part = 500 ms
first part = 2 s
seconds part = 800 ms
I want to be able to measure time elapsed (for frame time) with my Clock class. (Problem described below the code.)
Clock.h
typedef std::chrono::high_resolution_clock::time_point timePt;
class Clock
{
timePt currentTime;
timePt lastTime;
public:
Clock();
void update();
uint64_t deltaTime();
};
Clock.cpp
#include "Clock.h"
using namespace std::chrono;
Clock::Clock()
{
currentTime = high_resolution_clock::now();
lastTime = currentTime;
}
void Clock::update()
{
lastTime = currentTime;
currentTime = high_resolution_clock::now();
}
uint64_t Clock::deltaTime()
{
microseconds delta = duration_cast<microseconds>(currentTime - lastTime);
return delta.count();
}
When I try to use Clock like so
Clock clock;
while(1) {
clock.update();
uint64_t dt = clock.deltaTime();
for (int i=0; i < 10000; i++)
{
//do something to waste time between updates
int k = i*dt;
}
cout << dt << endl; //time elapsed since last update in microseconds
}
For me it prints about 30 times "0" until it finally prints a number which is always very close to something like "15625" microseconds (15.625 milliseconds).
My question is, why isn't there anything between? I'm wondering whether my implementation is wrong or the precision on high_resolution_clock is acting strange. Any ideas?
EDIT: I am using Codeblocks with mingw32 compiler on a windows 8 computer.
EDIT2:
I tried running the following code that should display high_resolution_clock precision:
template <class Clock>
void display_precision()
{
typedef std::chrono::duration<double, std::nano> NS;
NS ns = typename Clock::duration(1);
std::cout << ns.count() << " ns\n";
}
int main()
{
display_precision<std::chrono::high_resolution_clock>();
}
For me it prints: "1000 ns". So I guess high_resolution_clock has a precision of 1 microsecond right? Yet in my tests it seems to have a precision of 16 milliseconds?
What system are you using? (I guess it's Windows? Visual Studio is known to had this problem, now fixed in VS 2015, see the bug report). On some systems high_resolution_clock is defined as just an alias to system_clock, which can have really low resolution, like 16 ms you are seeing.
See for example this question.
I have the same problem with msys2 on Windows 10: the delta returned is 0 for most of my subfunctions tested and suddenly returns 15xxx or 24xxx microseconds. I thought there was a problem in my code as all the tutorials do not mention any problem.
Same thing for difftime(finish, start) in time.h which often returns 0.
I finally changed all my high_resolution clock with steady_clock, and I can find the proper times:
auto t_start = std::chrono::steady_clock::now();
_cvTracker->track(image); // my function to test
std::cout << "Time taken = " << std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::steady_clock ::now() - t_start).count() << " microseconds" << std::endl;
// returns the proper value (or at least a plausible value)
whereas this returns mostly 0:
auto t_start = std::chrono::high_resolution_clock::now();
_cvTracker->track(image); // my function to test
std::cout << "Time taken = " << std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::high_resolution_clock::now() - t_start).count() << " microseconds" << std::endl;
// returns 0 most of the time
difftime does not seem to work either:
time_t start, finish;
time(&start);
_cvTracker->track(image);
time(&finish);
std::cout << "Time taken= " << difftime(finish, start) << std::endl;
// returns 0 most of the time
how can I get current time with library boost. I can do this:
ptime now = boost::posix_timesecond_clock::local_time();
tm d_tm = to_tm(now);
But the last time unit of tm structure is second and I need in millisecond. Can I get current time with milliseconds?
look at boost::posix_time::microsec_clock::local_time()
#include <boost/date_time/posix_time/posix_time_types.hpp>
#include <iostream>
int
main()
{
boost::posix_time::ptime time = boost::posix_time::microsec_clock::local_time();
boost::posix_time::time_duration duration( time.time_of_day() );
std::cout << duration.total_milliseconds() << std::endl;
return 0;
}
I think the code should be:
ptime now = boost::posix_time::second_clock::local_time();
I think you forget the "::" in the codes. ^_^