std::chrono::system_clock::to_time_t

From cppreference.com

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros(C++20)
Language support library
Concepts library(C++20)
Diagnostics library
Memory management library
Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library(C++17)
Concurrency support library(C++11)
Execution control library(C++26)
Technical specifications
Symbols index
External libraries

[edit]

Date and time library

Time point
time_point (C++11)
clock_time_conversion (C++20)
clock_cast (C++20)
Duration
duration (C++11)
Clocks
system_clock (C++11)
steady_clock (C++11)
is_clock (C++20)
utc_clock (C++20)
tai_clock (C++20)
high_resolution_clock (C++11)
gps_clock (C++20)
file_clock (C++20)
local_t (C++20)
Time of day
is_amis_pm (C++20)(C++20)
make12make24 (C++20)(C++20)
hh_mm_ss (C++20)

Calendar
day (C++20)
month (C++20)
year (C++20)
weekday (C++20)
operator/ (C++20)
year_month_day (C++20)
year_month_day_last (C++20)
year_month_weekday (C++20)
year_month_weekday_last (C++20)
weekday_indexed (C++20)
weekday_last (C++20)
month_day (C++20)
month_day_last (C++20)
month_weekday (C++20)
month_weekday_last (C++20)
year_month (C++20)
last_speclast (C++20)(C++20)
`chrono` I/O
parse (C++20)

Time zone
tzdb (C++20)
tzdb_list (C++20)
get_tzdbget_tzdb_listreload_tzdbremote_version (C++20)(C++20)(C++20)(C++20)
sys_info (C++20)
local_info (C++20)
nonexistent_local_time (C++20)
ambiguous_local_time (C++20)
locate_zone (C++20)
current_zone (C++20)
time_zone (C++20)
choose (C++20)
zoned_traits (C++20)
zoned_time (C++20)
time_zone_link (C++20)
leap_second (C++20)
leap_second_info (C++20)
get_leap_second_info (C++20)
C-style date and time

[edit]

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

[edit]

staticstd::time_t to_time_t(const time_point& t)noexcept;		(since C++11)

Convertst to astd::time_t type.

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

[edit]Parameters

system clock time point to convert

[edit]Return value

Astd::time_t value representingt.

[edit]Example

Get the current time as astd::time_t two ways.

Run this code

#include <chrono>#include <ctime>#include <iostream>#include <thread>usingnamespace std::chrono_literals; int main(){// The old waystd::time_t oldt=std::time({}); std::this_thread::sleep_for(2700ms); // The new wayautoconst 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";}