Learn Converting Between Time Types | Formatting and Converting Time

When working with dates and times in C++, you will often encounter both modern <chrono> types and traditional C-style types. Interoperability between these representations is essential, especially when you need to use libraries or APIs that expect different formats. Understanding how to convert between std::chrono::system_clock::time_point, time_t, and struct tm allows you to bridge the gap between new and legacy code.

main.cpp


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

int main()
{
    // Get the current time as a time_point
    std::chrono::system_clock::time_point now = std::chrono::system_clock::now();

    // Convert time_point to time_t
    std::time_t now_c = std::chrono::system_clock::to_time_t(now);

    std::cout << "Current time as time_t: " << now_c << '\n';
    std::cout << "Current time as ctime: " << std::ctime(&now_c);
}

Converting a std::chrono::system_clock::time_point to time_t is a common operation when you need to interact with legacy APIs or functions that require a C-style time value. For example, functions like std::ctime, std::localtime, or third-party libraries may expect a time_t input, so being able to perform this conversion is crucial for compatibility and formatting.

main.cpp


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#include <iostream>
#include <ctime>

int main()
{
    // Get the current time as time_t
    std::time_t now = std::time(nullptr);

    // Convert time_t to struct tm in local time
    std::tm* local_tm = std::localtime(&now);

    std::cout << "Year: " << 1900 + local_tm->tm_year << '\n';
    std::cout << "Month: " << 1 + local_tm->tm_mon << '\n';
    std::cout << "Day: " << local_tm->tm_mday << '\n';
    std::cout << "Hour: " << local_tm->tm_hour << '\n';
    std::cout << "Minute: " << local_tm->tm_min << '\n';
    std::cout << "Second: " << local_tm->tm_sec << '\n';
}

Once you have a struct tm, you can easily access and manipulate individual components of the date and time, such as the year, month, day, hour, minute, and second. This structure is especially useful for custom formatting or for performing calculations and adjustments on the date and time values before further processing or output.

Note

Converting between time representations is often necessary when mixing modern and legacy code.

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Section 3. Chapter 1

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main.cpp


              123456789101112131415
            
#include <iostream>
#include <chrono>
#include <ctime>

int main()
{
    // Get the current time as a time_point
    std::chrono::system_clock::time_point now = std::chrono::system_clock::now();

    // Convert time_point to time_t
    std::time_t now_c = std::chrono::system_clock::to_time_t(now);

    std::cout << "Current time as time_t: " << now_c << '\n';
    std::cout << "Current time as ctime: " << std::ctime(&now_c);
}

main.cpp


              123456789101112131415161718
            
#include <iostream>
#include <ctime>

int main()
{
    // Get the current time as time_t
    std::time_t now = std::time(nullptr);

    // Convert time_t to struct tm in local time
    std::tm* local_tm = std::localtime(&now);

    std::cout << "Year: " << 1900 + local_tm->tm_year << '\n';
    std::cout << "Month: " << 1 + local_tm->tm_mon << '\n';
    std::cout << "Day: " << local_tm->tm_mday << '\n';
    std::cout << "Hour: " << local_tm->tm_hour << '\n';
    std::cout << "Minute: " << local_tm->tm_min << '\n';
    std::cout << "Second: " << local_tm->tm_sec << '\n';
}

Note

Converting between time representations is often necessary when mixing modern and legacy code.

Everything was clear?

Thanks for your feedback!

Section 3. Chapter 1