Type representing time intervals, supporting various units like seconds, milliseconds, microseconds.

Why is duration_cast needed?

Explicit casting is needed when converting from lower to higher units due to precision loss.

How to use duration literals?

From C++14, after using namespace std::chrono_literals; use like 10s, 500ms.

C++ duration | 'Time Interval' Guide

2025년 4월 30일 · 18분 읽기 · 수정 2026년 4월 7일 중급 Tutorial

이 글의 핵심

C++ duration C++, duration, "time, 1.

Introduction

std::chrono::duration is a type representing time intervals. It’s type-safe, has clear unit conversion, and supports time operations.

Reality in Production

When learning development, everything is clean and theoretical. But production is different. You wrestle with legacy code, chase tight deadlines, and face unexpected bugs. The content covered in this guide was initially learned as theory, but I realized “ah, that’s why it’s designed this way” while applying it to actual projects.

What stands out in my memory is the trial and error from my first project. I did it as I learned from books but spent days not knowing why it didn’t work. Eventually, I found the problem through a senior developer’s code review and learned a lot in the process. This guide covers not only theory but also pitfalls you may encounter in practice and their solutions.

1. duration Basics

Basic Usage

Here is detailed implementation code using C++. Import the necessary modules. Understand the role of each part while examining the code.

#include <chrono>
#include <iostream>

int main() {
    using namespace std::chrono;
    
    // Create time interval: duration type
    // std::chrono::seconds: seconds unit duration
    seconds sec(10);  // 10 seconds
    // std::chrono::milliseconds: milliseconds unit duration
    milliseconds ms(10000);  // 10000 milliseconds = 10 seconds
    // std::chrono::minutes: minutes unit duration
    minutes min(1);  // 1 minute = 60 seconds
    // std::chrono::hours: hours unit duration
    hours hr(1);  // 1 hour = 60 minutes = 3600 seconds
    
    // Get value: extract numeric value with count() method
    std::cout << "Seconds: " << sec.count() << std::endl;  // 10
    std::cout << "Milliseconds: " << ms.count() << std::endl;  // 10000
    
    return 0;
}

Standard duration Types

Below is an implementation example using C++. Import the necessary modules. Understand the role of each part while examining the code.

#include <chrono>

// C++11 standard units
std::chrono::hours h(1);
std::chrono::minutes m(60);
std::chrono::seconds s(3600);
std::chrono::milliseconds ms(3600000);
std::chrono::microseconds us(3600000000);
std::chrono::nanoseconds ns(3600000000000);

// All represent 1 hour

2. Time Conversion

Implicit Conversion (Higher → Lower)

Here is detailed implementation code using C++. Import the necessary modules. Understand the role of each part while examining the code.

#include <chrono>
#include <iostream>

int main() {
    using namespace std::chrono;
    
    seconds s(10);  // 10 seconds
    
    // ✅ Higher → Lower (implicit conversion possible)
    // Large unit → Small unit: no information loss
    // seconds → milliseconds: 10 seconds = 10000 milliseconds
    milliseconds ms = s;  // 10000ms (auto conversion)
    // seconds → microseconds: 10 seconds = 10000000 microseconds
    microseconds us = s;  // 10000000us (auto conversion)
    
    std::cout << "Milliseconds: " << ms.count() << std::endl;  // 10000
    std::cout << "Microseconds: " << us.count() << std::endl;  // 10000000
    
    return 0;
}

Explicit Conversion (Lower → Higher)

Here is detailed implementation code using C++. Import the necessary modules. Understand the role of each part while examining the code.

#include <chrono>
#include <iostream>

int main() {
    using namespace std::chrono;
    
    milliseconds ms(1500);  // 1500 milliseconds = 1.5 seconds
    
    // ❌ Lower → Higher (implicit not allowed)
    // Small unit → Large unit: possible information loss (truncate decimals)
    // seconds s = ms;  // Compile error: explicit conversion needed
    
    // ✅ duration_cast (explicit conversion)
    // duration_cast<seconds>: convert milliseconds to seconds
    // 1500ms → 1s (500ms truncated)
    seconds s = duration_cast<seconds>(ms);  // 1s (truncated)
    
    std::cout << "Seconds: " << s.count() << std::endl;  // 1
    
    return 0;
}

C++17 Rounding Functions

Here is detailed implementation code using C++. Import the necessary modules. Understand the role of each part while examining the code.

#include <chrono>
#include <iostream>

int main() {
    using namespace std::chrono;
    
    milliseconds ms(1500);  // 1500 milliseconds = 1.5 seconds
    
    // duration_cast: truncate (discard decimals)
    // 1.5 seconds → 1 second (0.5 seconds discarded)
    auto s1 = duration_cast<seconds>(ms);
    std::cout << "Truncate: " << s1.count() << "s" << std::endl;  // 1s
    
    // round: round (C++17)
    // 1.5 seconds → 2 seconds (round up since >= 0.5)
    auto s2 = round<seconds>(ms);
    std::cout << "Round: " << s2.count() << "s" << std::endl;  // 2s
    
    // ceil: ceiling (C++17)
    // 1.5 seconds → 2 seconds (always round up)
    auto s3 = ceil<seconds>(ms);
    std::cout << "Ceil: " << s3.count() << "s" << std::endl;  // 2s
    
    // floor: floor (C++17)
    // 1.5 seconds → 1 second (always round down, same as duration_cast)
    auto s4 = floor<seconds>(ms);
    std::cout << "Floor: " << s4.count() << "s" << std::endl;  // 1s
    
    return 0;
}

3. Time Operations

Arithmetic Operations

Here is detailed implementation code using C++. Import the necessary modules. Understand the role of each part while examining the code.

#include <chrono>
#include <iostream>

int main() {
    using namespace std::chrono;
    
    seconds s1(10);
    seconds s2(5);
    
    // Addition
    auto sum = s1 + s2;
    std::cout << "Sum: " << sum.count() << "s" << std::endl;  // 15s
    
    // Subtraction
    auto diff = s1 - s2;
    std::cout << "Diff: " << diff.count() << "s" << std::endl;  // 5s
    
    // Multiplication
    auto mul = s1 * 2;
    std::cout << "Multiply: " << mul.count() << "s" << std::endl;  // 20s
    
    // Division
    auto div = s1 / 2;
    std::cout << "Divide: " << div.count() << "s" << std::endl;  // 5s
    
    // Modulo
    auto mod = s1 % s2;
    std::cout << "Modulo: " << mod.count() << "s" << std::endl;  // 0s
    
    return 0;
}

Summary

Key Points

duration: Represents time intervals
Standard types: hours, minutes, seconds, milliseconds, etc.
Conversion: Implicit (higher→lower), explicit (lower→higher)
Operations: Arithmetic and comparison supported
Literals: C++14 supports 10s, 500ms syntax

When to Use

✅ Use duration when:

Need type-safe time intervals
Want clear unit conversion
Measuring elapsed time
Implementing timeouts

❌ Don’t use when:

Simple integer milliseconds sufficient
Need calendar dates (use time_point)

Best Practices

✅ Use appropriate unit for context
✅ Use literals for readability (C++14+)
✅ Use duration_cast for explicit conversion
❌ Don’t mix units without conversion
❌ Don’t use raw integers for time

Master duration for type-safe time handling! 🚀

자주 묻는 질문 (FAQ)

Q. 이 내용을 실무에서 언제 쓰나요?

A. Everything about C++ duration : from basic concepts to practical applications.

Q. 선행으로 읽으면 좋은 글은?

A. 각 글 하단의 이전 글 또는 관련 글 링크를 따라가면 순서대로 배울 수 있습니다. C++ 시리즈 목차에서 전체 흐름을 확인할 수 있습니다.

Q. 더 깊이 공부하려면?

A. cppreference와 해당 라이브러리 공식 문서를 참고하세요. 글 말미의 참고 자료 링크도 활용하면 좋습니다.

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이 글의 핵심

Introduction

Reality in Production

1. duration Basics

Basic Usage

Standard duration Types

2. Time Conversion

Implicit Conversion (Higher → Lower)

Explicit Conversion (Lower → Higher)

C++17 Rounding Functions

3. Time Operations

Arithmetic Operations

Summary

Key Points

When to Use

Best Practices

Related Articles

자주 묻는 질문 (FAQ)

Q. 이 내용을 실무에서 언제 쓰나요?

Q. 선행으로 읽으면 좋은 글은?

Q. 더 깊이 공부하려면?

같이 보면 좋은 글 (내부 링크)

이 글에서 다루는 키워드 (관련 검색어)

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