Is there a simple way to calculate a time difference in ms?

Question

Is there a simple way to calculate a time difference in ms?

Markus Freitag 3,791

Once with local time?

Once with UTC +0 time. So I have to convert times first.

auto t_start = std::chrono::high_resolution_clock::now();
    // the work...
auto t_end = std::chrono::high_resolution_clock::now();
double elapsed_time_ms = std::chrono::duration<double, std::milli>(t_end - t_start).count();

Option 1 Check the current time // the work Check the current time, calculate the difference in ms. Not more.

Option 2: Input from database as UTC + 0 // the work Check the current time, calculate the difference in ms. First convert to UTC + 0 Not more.

What I have? VS2017 C++ Prof. https://en.cppreference.com/w/cpp/chrono/utc_clock so not possible for me.

How can I initialize this time? Then calculate the difference.

    auto t_start = // from my database           std::chrono::high_resolution_clock::now();   
	// the work...
	auto t_end = std::chrono::high_resolution_clock::now();

	double elapsed_time_ms = std::chrono::duration<double, std::milli>(t_end - t_start).count();

No problem if both side use the same time.

I need a solution for both option. Hope is clear what I need soon.

Minxin Yu 13,506 Reputation points Microsoft External Staff

2024-01-18T02:24:43.1733333+00:00

I'm not quite understand what your problem point is.
utc_clock is provided in C++20.
Consider using Visual Studio 2022 Community Version (Free for individuals).

Markus Freitag 3,791

// ** My time on the PC UTC + 0
time_t now = time(0); // UTC 

// ** From database is always comining with UTC + 0
tm tmFromDatabase;
tmFromDatabase.tm_year = std::stoi("2024") - 1900;
tmFromDatabase.tm_mon = std::stoi("01");
tmFromDatabase.tm_mday = std::stoi("18");
tmFromDatabase.tm_hour = std::stoi("11");
tmFromDatabase.tm_min = std::stoi("14");
tmFromDatabase.tm_sec = std::stoi("00");

time_t ttFromDatabase = mktime(&tmFromDatabase); 
time_t diffUTC_0 = now - ttFromDatabase;

Now I need the difference in seconds and milliseconds. Not more. Is the initialization correct? What is the best way to do that?

https://stackoverflow.com/questions/22373541/how-to-know-the-difference-of-gmt-and-local-time-in-c-on-solaris
now = time(0); // UTC
time_t diff;
struct tm* ptmgm = gmtime(&now); 
time_t gmnow = mktime(ptmgm);
diff = gmnow - now;
if (ptmgm->tm_isdst > 0) {
	diff = diff - 60 * 60;
}

Consider using Visual Studio 2022 Community Version (Free for individuals). Is not possible, should run with VS2017.

Answer accepted by question author

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Your answer

Minxin Yu 13,506 Reputation points Microsoft External Staff

2024-01-18T02:24:43.1733333+00:00

I'm not quite understand what your problem point is.
utc_clock is provided in C++20.
Consider using Visual Studio 2022 Community Version (Free for individuals).
Markus Freitag 3,791 Reputation points

2024-01-18T18:04:52.6333333+00:00

// ** My time on the PC UTC + 0 time_t now = time(0); // UTC // ** From database is always comining with UTC + 0 tm tmFromDatabase; tmFromDatabase.tm_year = std::stoi("2024") - 1900; tmFromDatabase.tm_mon = std::stoi("01"); tmFromDatabase.tm_mday = std::stoi("18"); tmFromDatabase.tm_hour = std::stoi("11"); tmFromDatabase.tm_min = std::stoi("14"); tmFromDatabase.tm_sec = std::stoi("00"); time_t ttFromDatabase = mktime(&tmFromDatabase); time_t diffUTC_0 = now - ttFromDatabase;

Now I need the difference in seconds and milliseconds. Not more. Is the initialization correct? What is the best way to do that?

https://stackoverflow.com/questions/22373541/how-to-know-the-difference-of-gmt-and-local-time-in-c-on-solaris now = time(0); // UTC time_t diff; struct tm* ptmgm = gmtime(&now); time_t gmnow = mktime(ptmgm); diff = gmnow - now; if (ptmgm->tm_isdst > 0) { diff = diff - 60 * 60; }

Consider using Visual Studio 2022 Community Version (Free for individuals). Is not possible, should run with VS2017.

Answer 1

Minxin Yu 13,506 Microsoft External Staff

Hi, @Markus Freitag

Considering your time on the PC UTC + 0

tmFromDatabase.tm_mon = std::stoi("01")-1; // from 0 -11

use std::chrono::system_clock::now() to get the accurate time(ms).

	auto currentTime = std::chrono::system_clock::now();
	auto difference_ms = std::chrono::duration_cast<std::chrono::milliseconds>(currentTime - std::chrono::system_clock::from_time_t(std::mktime(&dbTime))).count();

Best regards,

Minxin Yu

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Markus Freitag 3,791

I'm sorry, that was a misunderstanding.

My PC use UTC + 1 in winter time.
My PC use UTC + 2 in summer time.

The idea is now to detect the time from my PC with UTC + 0. I always get UTC 0 time from the database independent of winter and summer time or USA Europe, China I think the problem is how I detect and initialize the time of the database.

//tmFromDatabase.tm_mon = std::stoi("01")-1; // from 0 -11  in winter time?
//tmFromDatabase.tm_mon = std::stoi("01")-2; // from 0 -11  in summer time?
//Problem -1 or -2 should be automatically calculate.

inputDatabase = "2024-01-19 13:50:22"   (UTC + 0)
long GetDifferenceTimeIn_ms(CString inputDatabase)
{
	// Capture the current time
	// Send back the time difference in ms
	
	const auto now = std::chrono::system_clock::now();
    const std::time_t t_c = std::chrono::system_clock::to_time_t(now);
    std::cout << "The system clock is currently at " << std::ctime(&t_c);
	
	auto difference_ms = std::chrono::duration_cast<std::chrono::milliseconds>(currentTime - std::chrono::system_clock::from_time_t(std::mktime(&dbTime))).count();
	
	auto currentTime = std::chrono::system_clock::now();
	auto difference_ms = std::chrono::duration_cast<std::chrono::milliseconds>(currentTime - std::chrono::system_clock::from_time_t(std::mktime(&dbTime))).count();
	
// Second attempts
    tm tmFromDatabase;
	tmFromDatabase.tm_year = std::stoi("2024") - 1900;
	tmFromDatabase.tm_mon = std::stoi("01") -1; //+ 1;// -1;
	tmFromDatabase.tm_mday = std::stoi("19");
	tmFromDatabase.tm_hour = std::stoi("10");
	tmFromDatabase.tm_min = std::stoi("54");
	tmFromDatabase.tm_sec = std::stoi("00");

	const auto nowTime = std::chrono::system_clock::now();
	const std::time_t t_c2 = std::chrono::system_clock::to_time_t(nowTime);
	
	auto retDatabase = std::chrono::system_clock::from_time_t(std::mktime(&tmFromDatabase));
	auto z2 = retDatabase - nowTime;

	CString sTest;
	sTest.Format("The system clock is currently at %s", CString(std::ctime(&t_c2))); // here is showing local time utc+1 Europe

	time_t x1= mktime(&tmFromDatabase);

	auto difference_msNew = std::chrono::duration_cast<std::chrono::milliseconds>(nowTime - std::chrono::system_clock::from_time_t(std::mktime(&tmFromDatabase))).count();
	auto difference_sNew = std::chrono::duration_cast<std::chrono::seconds>(nowTime - std::chrono::system_clock::from_time_t(std::mktime(&tmFromDatabase))).count();
}

enter image description here

Markus Freitag 3,791 Reputation points

2024-01-21T18:01:20.9566667+00:00

The goal is simple!

Input every time with UTC + 0

My application sometimes has +1 +2 or more. The idea would be to set everything to UTC + 0 and then calculate the millisseconds. Hope someone can help me and solve it easily. Thank you in advance.
Minxin Yu 13,506 Reputation points Microsoft External Staff

2024-01-22T03:00:24.1733333+00:00

Currently, the Windows API only provides APIs for conversion between system time and UTC. If your program has times in multiple time zones (+1,+2), then create a custom method to manually add or subtract hours to convert to UTC 0 and use std::chrono::duration_cast<std::chrono::milliseconds>.
Markus Freitag 3,791 Reputation points

2024-01-22T07:54:18.9166667+00:00

https://en.wikipedia.org/wiki/Summer_time_in_Europe

Can you make a sample please?
Input from database is every time this. 22.01.2024 09:05:00 utc + 0

Thanks!
Minxin Yu 13,506 Reputation points Microsoft External Staff

2024-01-22T08:43:04.2533333+00:00
To compare the time differences, you can handle the database time instead of local time . Convert UTC 0 -> local time zone.
GetTimeZoneInformation TIME_ZONE_INFORMATION member Bias gets the offset.

tmFromDatabase.tm_hour = std::stoi("10");// handle the UTC hour here(just add or subtract), +1 in winter time or +2 in summer time

It will be easier and won't cause the local time to lose accuracy(ms).|
RLWA32 51,456 Reputation points

2024-01-22T10:56:51.1366667+00:00

@Markus Freitag If the database only contains times in UTC then its a simple thing to calculate time differences in UTC. Offsets from UTC for Daylight Time or Summer Time would not be relevant. Are you also concerned with converting UTC to local time in multiple time zones? By multiple time zones I don't mean Daylight/Summer because those are offsets, not time zones.
Markus Freitag 3,791 Reputation points

2024-01-22T14:10:06.86+00:00

Convert UTC 0 -> local time zone.
GetTimeZoneInformation TIME_ZONE_INFORMATION member Bias gets the offset.

Can you make a whole sample please? Thanks in advance.
Markus Freitag 3,791 Reputation points

2024-01-22T14:14:19.7066667+00:00

If the database only contains times in UTC then its a simple thing to calculate time differences in UTC.

Can you make please a sample, that would be the best and easiest for VS2017, C++, MFC

I don't have https://en.cppreference.com/w/cpp/chrono/utc_clock

It must run in VS2017 Prof, MFC C++

Thanks in advance.

RLWA32 51,456

For example,

// UTC date/time 1/22/2024 3:25 pm
tm tmFromDatabase{};
tmFromDatabase.tm_year = std::stoi("2024") - 1900;
tmFromDatabase.tm_mon = std::stoi("01") - 1; 
tmFromDatabase.tm_mday = std::stoi("22");
tmFromDatabase.tm_hour = std::stoi("15");
tmFromDatabase.tm_min = std::stoi("25");
tmFromDatabase.tm_sec = std::stoi("00");

time_t now = time(nullptr);
time_t dbt = _mkgmtime(&tmFromDatabase);
time_t diff = now - dbt; // seconds
time_t diff_ms = diff * 1000;  //milliseconds

Barry Schwarz 4,871 Reputation points

2024-01-22T23:10:30.05+00:00

Since time_t is an integer type, will this do what he wants?
RLWA32 51,456 Reputation points

2024-01-23T00:08:08.4233333+00:00

@Barry Schwarz I thought that would achieve the questioner's objective of calculating a difference between two UTC time points. Each of the time_t values represents seconds.
Markus Freitag 3,791 Reputation points

2024-01-23T15:34:07.58+00:00

My Window system time 13:14:10

From database 13:14:00

The result: Why I need -1 for tm_mon ? Picture

What would I have expected?

Between 1 and 20 seconds. Input every time utc + 0 My time is at moment utc + 1 What is the right way?
RLWA32 51,456 Reputation points

2024-01-23T18:23:20.8866667+00:00
I took the two time_t values from your posted image (1706012044, 1706015640) and converted them to tm structs using gmtime_s.

time_t mfnow = 1706012044; time_t mfdbt = 1706015640; tm tmnow{}, tmdbt{}; errno_t err = gmtime_s(&tmnow, &mfnow); err = gmtime_s(&tmdbt, &mfdbt);

The resulting tm structs contained the following information (in UTC).

The tmdbt struct contained member values that agreed with your own tmDataBase struct. However, the tmnow struct represented 12:14:4 UTC. The reason you obtained a negative value for the time difference was because when your code executed it subtracted a future time value from the then current time. Since the tm structure uses 0 to represent the month of January 1 is subtracted from the value obtained from std:stoi("01") to conform to the structure's requirement.

Markus Freitag 3,791

You are right! Thanks! My current time on PC 24.01.2024 13:28:00 Input with UTC + 0

tm tmFromDatabase{};  // UTC + 0
tmFromDatabase.tm_year = std::stoi("2024") - 1900;
tmFromDatabase.tm_mon = std::stoi("01") - 1;
tmFromDatabase.tm_mday = std::stoi("24");
tmFromDatabase.tm_hour = std::stoi("12");
tmFromDatabase.tm_min = std::stoi("27");
tmFromDatabase.tm_sec = std::stoi("00");

time_t now = time(nullptr); // Calculate system time to UTC + 0, right?

time_t dbt = _mkgmtime(&tmFromDatabase);
time_t diff = now - dbt; // seconds
time_t diff_ms = diff * 1000;  //milliseconds

Summary, looks good now, easy and possible with Visual Studio 2017, MFC

Last question // time(nullptr) means Calculate system time to UTC + 0, right? OK__3_

RLWA32 51,456 Reputation points

2024-01-24T16:50:49.0366667+00:00

From the docs "The time function returns the number of seconds elapsed since midnight (00:00:00), January 1, 1970, Coordinated Universal Time (UTC), according to the system clock. The return value is stored in the location given by destTime. This parameter may be NULL, in which case the return value isn't stored."
Markus Freitag 3,791 Reputation points

2024-01-28T17:41:24.4233333+00:00

Thank you!

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Is there a simple way to calculate a time difference in ms?

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