NAME¶

std::chrono::utc_clock::now - std::chrono::utc_clock::now

Synopsis¶

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.

Parameters¶

(none)

Return value¶

A time point representing the current time.

Example¶

// Run this code

#include <iostream>
#include <iomanip>
#include <vector>
#include <numeric>
#include <chrono>

volatile int sink;
int main()
{
std::cout << std::fixed << std::setprecision(9) << std::left;
for (auto size = 1ull; size < 1000'000'000ull; size *= 100) {
// record start time
auto start = std::chrono::utc_clock::now();
// do some work
std::vector<int> v(size, 42);
sink = std::accumulate(v.begin(), v.end(), 0u); // make sure it's a side effect
// record end time
auto end = std::chrono::utc_clock::now();
std::chrono::duration<double> diff = end - start;
std::cout << "Time to fill and iterate a vector of " << std::setw(9)
<< size << " ints : " << diff.count() << " s\n";
}
}

Possible output:¶

Time to fill and iterate a vector of 1 ints : 0.000006568 s
Time to fill and iterate a vector of 100 ints : 0.000002854 s
Time to fill and iterate a vector of 10000 ints : 0.000116290 s
Time to fill and iterate a vector of 1000000 ints : 0.011742752 s
Time to fill and iterate a vector of 100000000 ints : 0.505534949 s