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Date and time library - cppreference.com

C++ includes support for two types of time manipulation:

• The chrono library, a flexible collection of types that track time with varying degrees of precision (e.g., std::chrono::time_point).
• C-style date and time library (e.g., std::time).

The chrono library defines several main types as well as utility functions and common typedefs:

• clocks
• time points
• durations

A clock consists of a starting point (or epoch) and a tick rate. For example, a clock may have an epoch of January 1, 1970 and tick every second. C++ defines several clock types:

A time point is a duration of time that has passed since the epoch of a specific clock.

A duration consists of a span of time, defined as some number of ticks of some time unit. For example, "42 seconds" could be represented by a duration consisting of 42 ticks of a 1-second time unit.

hh_mm_ss splits a duration representing time elapsed since midnight into hours, minutes, seconds, and fractional seconds, as applicable. It is primarily a formatting tool.

Also provided are the C-style date and time functions, such as std::time_t, std::difftime, and CLOCKS_PER_SEC.

#include <chrono>
#include <iostream>
 
long Fibonacci(unsigned n)
{
    return n < 2 ? n : Fibonacci(n - 1) + Fibonacci(n - 2);
}
 
int main()
{
    // Measures and displays an execution time of a function call.
    const auto start{std::chrono::steady_clock::now()};
    const auto fb{Fibonacci(42)};
    const auto finish{std::chrono::steady_clock::now()};
    const std::chrono::duration<double> elapsed_seconds{finish - start};
 
    std::cout << "Fibonacci(42): " << fb << "\nElapsed time: ";
//  std::cout << elapsed_seconds.count() << "s\n"; // Before C++20
    std::cout << elapsed_seconds << '\n'; // C++20's chrono::duration operator<<
 
    // Prints UTC and local time.
    const auto tp_utc{std::chrono::system_clock::now()};
    std::cout << "Current time 'UTC' is: " << tp_utc << "\n"
                 "Current time 'Local' is: "
              << std::chrono::current_zone()->to_local(tp_utc) << '\n';
}

Possible output:

Fibonacci(42): 267914296
Elapsed time: 0.728532s
Current time 'UTC' is: 2025-02-10 06:22:39.420666960
Current time 'Local' is: 2025-02-10 09:22:39.420666960

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