std::chrono::system_clock::now

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)

Dynamic memory management

Error handling

Program utilities

Variadic functions

Date and time

Function objects

initializer_list (C++11)

bitset

hash (C++11)

Relational operators

rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=

optional, any and variant (C++17)

optional

any

variant

in_placein_place_typein_place_indexin_place_tin_place_type_tin_place_index_t

Pairs and tuples

pair

tuple (C++11)

apply (C++17)

make_from_tuple (C++17)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

integer_sequence (C++14)

Swap, forward and move

swap

exchange (C++14)

forward (C++11)

move (C++11)

move_if_noexcept (C++11)

Elementary string conversions

to_chars (C++17)

from_chars (C++17)

chars_format (C++17)

Type operations

declval (C++11)

as_const (C++17)

 

Date and time utilities

time_point (C++11)

duration (C++11)

system_clock (C++11)

steady_clock (C++11)

high_resolution_clock (C++11)

C-style date and time

 

std::chrono::system_clock

Member functions

system_clock::now

system_clock::to_time_t

system_clock::from_time_t

 

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

Returns a time point representing the current point in time.

Parameters

(none)

Return value

A time point representing the current time.

Exceptions

noexcept specification:  

noexcept

  

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::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 " 
                  << 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