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std::chrono::system_clock:: to_time_t

From cppreference.net
C++
Date and time library
std::chrono::system_clock
static std:: time_t to_time_t ( const time_point & t ) noexcept ;
(since C++11)

Converts t to a std::time_t type.

If std::time_t has lower precision, it is implementation-defined whether the value is rounded or truncated.

Contents

Parameters

t - system clock time point to convert

Return value

A std::time_t value representing t .

Example

Get the current time as a std::time_t two ways.

Run this code 
#include <chrono>
#include <ctime>
#include <iostream>
#include <thread>
using namespace std::chrono_literals;
int main()
{
    // The old way
    std::time_t oldt = std::time({});
    std::this_thread::sleep_for(2700ms);
    // The new way
    auto const now = std::chrono::system_clock::now();
    std::time_t newt = std::chrono::system_clock::to_time_t(now);
    std::cout << "newt - oldt == " << newt - oldt << " s\n";
}

Possible output: 

newt - oldt == 3 s

See also

[static]
converts std::time_t to a system clock time point
(public static member function)