std::chrono::system_clock::now

 

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duration (C++11)
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chrono I/O
parse (C++20)
C-style date and time

 

std::chrono::system_clock

Member functions

system_clock::now

system_clock::to_time_t

system_clock::from_time_t

Time point I/O

operator<<

formatter<std::chrono::sys_time>

from_stream

 

static std::chrono::time_point<std::chrono::system_clock> now() noexcept;		(since C++11)

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::system_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::system_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