std::chrono::utc_clock::now

 

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C-style date and time

 

std::chrono::utc_clock

Member functions

utc_clock::now

utc_clock::to_sys

utc_clock::from_sys

Time point I/O

operator<<

formatter<std::chrono::utc_time>

from_stream

Leap second insertion information

leap_second_info

get_leap_second_info

 

static std::chrono::time_point<std::chrono::utc_clock> now();		(since C++20)

Returns a time point representing the current point in time. The result is calculated as if by std::chrono::utc_clock::from_sys(std::chrono::system_clock::now()). Implementations may use a more accurate value of UTC time.

Return value

A time point representing the current time.

Example

Run this code

#include <chrono>
#include <cstddef>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <vector>
 
volatile int sink; // prevents optimization
 
void do_some_work(std::size_t size)
{
    std::vector<int> v(size, 42);
    sink = std::accumulate(v.begin(), v.end(), 0); // ensures side effect
}
 
int main()
{
    std::cout << std::fixed << std::setprecision(9) << std::left;
    for (auto size{1ull}; size < 1000'000'000ull; size *= 100)
    {
        const auto start = std::chrono::utc_clock::now();
        do_some_work(size);
        const auto end = std::chrono::utc_clock::now();
        const std::chrono::duration<double> diff = end - start;
        std::cout << "start = " << start << "; end = " << end << ";\n";
        std::cout << "diff = " << diff << "; size = " << size << '\n';
    }
}

Possible output:

start = 2024-10-25 13:37:42.016233947; end = 2024-10-25 13:37:42.016239362;
diff = 0.000005415s; size = 1
start = 2024-10-25 13:37:42.016384595; end = 2024-10-25 13:37:42.016386581;
diff = 0.000001986s; size = 100
start = 2024-10-25 13:37:42.016394197; end = 2024-10-25 13:37:42.016445830;
diff = 0.000051633s; size = 10000
start = 2024-10-25 13:37:42.016452737; end = 2024-10-25 13:37:42.022496657;
diff = 0.006043920s; size = 1000000
start = 2024-10-25 13:37:42.022511298; end = 2024-10-25 13:37:42.658639946;
diff = 0.636128648s; size = 100000000