Formatting time with std::chrono

20 Oct 2023

One common task in programming is to format time in a specific way. The C++ standard library provides the std::chrono library which is a powerful and flexible tool for dealing with time-related operations.

In this blog post, we will explore how to use std::chrono to format time in various ways, such as converting it to a string or extracting individual time components.

Formatting time as a string

To format time as a string, we can make use of the std::put_time function from the <iomanip> header. This function allows us to format a std::chrono::time_point object into a string using a format specifier.

Here’s an example to format the current local time as a string:

#include <iostream>
#include <iomanip>
#include <chrono>

int main() {
    auto current_time = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());
    std::cout << std::put_time(std::localtime(&current_time), "%F %T") << std::endl;
    return 0;
}

In this example, we retrieve the current local time as a std::chrono::time_point object using std::chrono::system_clock::now(). We then convert it to a std::time_t object using std::chrono::system_clock::to_time_t(). Finally, we pass this std::time_t object to std::put_time along with the desired format specifier (“%F %T”) to get the formatted string representation of the time.

The output of the above example might look like: “2022-05-28 15:30:00”.

Extracting individual time components

std::chrono also provides various facilities to extract individual time components such as hours, minutes, and seconds from a std::chrono::time_point.

Here’s an example to extract the current hour from the local time:

#include <iostream>
#include <chrono>

int main() {
    auto current_time = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());
    auto local_time = *std::localtime(&current_time);
    auto hour = local_time.tm_hour;
    std::cout << "Current hour: " << hour << std::endl;
    return 0;
}

In this example, we retrieve the current local time as a std::chrono::time_point object and then convert it to a std::time_t object. We then use std::localtime to convert the std::time_t object into a std::tm object which represents the local time. Finally, we access the tm_hour member of std::tm to get the current hour.

The output of the above example might look like: “Current hour: 15”.

Conclusion

Formatting time is a common task in programming, and the std::chrono library provides a flexible and efficient way to achieve this in C++. In this blog post, we explored how to format time as a string using std::put_time and how to extract individual time components using std::tm. By using these tools, you can accurately and easily handle time-related operations in your C++ programs.

Formatting time as a string

Extracting individual time components

Conclusion

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