std::chrono::file_clock::now(3)

NAME
std::chrono::file_clock::now - std::chrono::file_clock::now

Synopsis
   static std::chrono::time_point<std::chrono::file_clock> now() (since C++20)
   noexcept;
   Returns a time point representing the current point in 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::file_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::file_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