std::chrono::file_clock::now

C++

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C-style date and time

std::chrono::file_clock

Member functions

file_clock::now

file_clock::to_sysfile_clock::from_sys (provided only if to_utc and from_utc are not provided)

file_clock::to_utcfile_clock::from_utc (provided only if to_sys and from_sys are not provided)

Time point I/O

operator<<

to_stream

from_stream

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

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 <vector>
#include <numeric>
#include <chrono>

volatile int sink;
int main()
{
    for (auto size = 1ull; size < 1000000000ull; 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 " 
                  << size << " ints: " << diff.count() << " s\n";
    }
}

Possible output:

Time to fill and iterate a vector of 1 ints: 2.43e-07 s
Time to fill and iterate a vector of 100 ints: 4.1e-07 s
Time to fill and iterate a vector of 10000 ints: 2.519e-05 s
Time to fill and iterate a vector of 1000000 ints: 0.00207669 s
Time to fill and iterate a vector of 100000000 ints: 0.423087 s