chrono

chrono (since C++11)

---

Prerequisites

---

1. What is <chrono>?

<chrono> is the C++ standard library for time measurement and manipulation.

It provides:

• Clocks → get current time
• Durations → represent time intervals
• Time points → represent a point in time

Designed to be type-safe and precise

Use it when:

• measuring execution time
• handling time durations
• implementing timers or delays
• writing performance-critical code

Duration

Represents a time interval

std::chrono::duration<Rep, Period>

• Rep → numeric type (e.g., int, double)
• Period → time unit (ratio)

std::chrono::seconds
std::chrono::milliseconds
std::chrono::microseconds
std::chrono::nanoseconds

Time Point

Represents a specific point in time

std::chrono::time_point<Clock>

Always associated with a clock

Clock

Provides the current time

Types of Clocks

std::chrono::system_clock
std::chrono::steady_clock
std::chrono::high_resolution_clock

2. How to use

✔️ Measuring Execution Time

#include <iostream>
#include <chrono>

int main()
{
    auto start = std::chrono::high_resolution_clock::now();

    // code to measure
    for (int i = 0; i < 1000000; ++i)
    {

    }

    auto end = std::chrono::high_resolution_clock::now();

    auto duration = end - start;
    std::chrono::duration_cast<std::chrono::microseconds>(duration).count();
}

✔️ Create Duration

std::chrono::seconds s(5);
std::chrono::milliseconds ms(1500);

✔️ Arithmetic

auto total = s + std::chrono::seconds(3);  // 8 seconds

✔️ Conversion

auto ms = std::chrono::duration_cast<std::chrono::milliseconds>(s);

✔️ Access Value

ms.count();  // returns numeric value

2-1. Clocks Explained

system_clock

• Represents real-world wall clock time
• Can be adjusted (NTP, user changes)

Use for:

• timestamps
• logging

steady_clock

• Monotonic (never goes backward)
• Not affected by system time changes

Use for:

• measuring durations
• performance timing

high_resolution_clock

• Highest available precision
• Often alias of one of the above

Use when you need maximum precision

Clock	Stable	Affected by System Time	Use Case
system_clock	❌	✅	real-world time
steady_clock	✅	❌	benchmarking
high_resolution_clock	depends	depends	high precision

2-2. Sleep

#include <thread>

std::this_thread::sleep_for(std::chrono::seconds(1));
std::this_thread::sleep_until(std::chrono::steady_clock::now() + std::chrono::seconds(1));

2-3. Getting Current Time

#include <iostream>
#include <chrono>
#include <ctime>

int main()
{
    auto now = std::chrono::system_clock::now();

    std::time_t time = std::chrono::system_clock::to_time_t(now);

    std::cout << std::ctime(&time);
}