std::strftime(3)

📦 version 2024.07.05, in nixpkgs unstable, opensuse-leap 16.0

👑 std::strftime(3) — C++ Standard Library 👑

ok so this is the std::strftime page from the C++ Standard Libary (yes bestie, that's how they spelled it, we're not fixing it 💅) and it's long, so buckle up. Part 1 is right here, part 2 is coming, do not panic.

🌸 NAME 🌸

std::strftime — it's literally std::strftime, that's the whole name, no notes 🎀

✨ SYNOPSIS ✨

This little icon is defined in header <ctime>, and here's the signature, character-for-character, don't touch it:

std::size_t strftime( char* str, std::size_t count, const char* format, const std::tm* tp );

So what's the vibe? It takes the date-and-time info from a given calendar time tp and converts it into a null-terminated multibyte character string str, according to the format string format. Up to count bytes get written. It's giving "glow-up your tm struct into pretty text" energy ✨

💖 PARAMETERS 💖

Here's who's who in the group chat:

str — pointer to the first element of the char array where the output goes.
count — maximum number of bytes to write.
format — pointer to a null-terminated multibyte character string that specifies the format of the conversion.
tp — pointer to the object containing the date and time information to be converted.

🧚 Format string 🧚

ok so this is the main character of the whole page, pay attention bestie 🙈

The format string is made up of zero or more conversion specifiers plus ordinary characters (except %). Every ordinary character — including the terminating null character — gets copied to the output string without modification, no cap.

Each conversion specification starts with a % character, optionally followed by an E or O modifier (ignored if unsupported by the locale — important!!), and then followed by the character that determines the behavior of the specifier.

Here are all the format specifiers available, sorted into their little categories ⬇️

🌈 Year

% — writes a literal %. The full conversion specification must be %%.
%n (C++11) — writes a newline character.
%t (C++11) — writes a horizontal tab character.
%Y — writes the year as a decimal number, e.g. 2017. (field: tm_year)
%EY (C++11) — writes the year in the alternative representation, e.g. 平成23年 (year Heisei 23) instead of 2011年 (year 2011) in the ja_JP locale. (field: tm_year)
%y — writes the last 2 digits of the year as a decimal number (range [00,99]). (field: tm_year)
%Oy (C++11) — writes the last 2 digits of the year using the alternative numeric system, e.g. 十一 instead of 11 in the ja_JP locale. (field: tm_year)
%Ey (C++11) — writes the year as an offset from the locale's alternative calendar period %EC (locale-dependent). (field: tm_year)
%C (C++11) — writes the first 2 digits of the year as a decimal number (range [00,99]). (field: tm_year)
%EC (C++11) — writes the name of the base year (period) in the locale's alternative representation, e.g. 平成 (Heisei era) in ja_JP. (field: tm_year)
%G (C++11) — writes the ISO 8601 week-based year, i.e. the year that contains the specified week. (fields: tm_year, tm_wday, tm_yday)

In ISO 8601, weeks begin with Monday and the first week of the year must satisfy the following requirements:

Includes January 4
Includes first Thursday of the year

%g (C++11) — writes the last 2 digits of the ISO 8601 week-based year, i.e. the year that contains the specified week (range [00,99]). (fields: tm_year, tm_wday, tm_yday)

In ISO 8601, weeks begin with Monday and the first week of the year must satisfy the following requirements:

Includes January 4
Includes first Thursday of the year

🎀 Month

%b — writes the abbreviated month name, e.g. Oct (locale dependent). (field: tm_mon)
%h (C++11) — synonym of %b. (field: tm_mon)
%B — writes the full month name, e.g. October (locale dependent). (field: tm_mon)
%m — writes the month as a decimal number (range [01,12]). (field: tm_mon)
%Om (C++11) — writes the month using the alternative numeric system, e.g. 十二 instead of 12 in the ja_JP locale. (field: tm_mon)

🦋 Week

%U — writes the week of the year as a decimal number (Sunday is the first day of the week) (range [00,53]). (fields: tm_year, tm_wday, tm_yday)
%OU (C++11) — writes the week of the year, as by %U, using the alternative numeric system, e.g. 五十二 instead of 52 in the ja_JP locale. (fields: tm_year, tm_wday, tm_yday)
%W — writes the week of the year as a decimal number (Monday is the first day of the week) (range [00,53]). (fields: tm_year, tm_wday, tm_yday)
%OW (C++11) — writes the week of the year, as by %W, using the alternative numeric system, e.g. 五十二 instead of 52 in the ja_JP locale. (fields: tm_year, tm_wday, tm_yday)
%V (C++11) — writes the ISO 8601 week of the year (range [01,53]). (fields: tm_year, tm_wday, tm_yday)

In ISO 8601, weeks begin with Monday and the first week of the year must satisfy the following requirements:

Includes January 4
Includes first Thursday of the year

%OV (C++11) — writes the week of the year, as by %V, using the alternative numeric system, e.g. 五十二 instead of 52 in the ja_JP locale. (fields: tm_year, tm_wday, tm_yday)

🍓 Day of the year/month

%j — writes the day of the year as a decimal number (range [001,366]). (field: tm_yday)
%d — writes the day of the month as a decimal number (range [01,31]). (field: tm_mday)
%Od (C++11) — writes the zero-based day of the month using the alternative numeric system, e.g. 二十七 instead of 27 in the ja_JP locale. (field: tm_mday)

A single character is preceded by a space.

%e (C++11) — writes the day of the month as a decimal number (range [1,31]). (field: tm_mday)

A single digit is preceded by a space.

%Oe (C++11) — writes the one-based day of the month using the alternative numeric system, e.g. 二十七 instead of 27 in the ja_JP locale. (field: tm_mday)

A single character is preceded by a space.

💜 Day of the week

%a — writes the abbreviated weekday name, e.g. Fri (locale dependent). (field: tm_wday)
%A — writes the full weekday name, e.g. Friday (locale dependent). (field: tm_wday)
%w — writes the weekday as a decimal number, where Sunday is 0 (range [0-6]). (field: tm_wday)
%Ow (C++11) — writes the weekday, where Sunday is 0, using the alternative numeric system, e.g. 二 instead of 2 in the ja_JP locale. (field: tm_wday)
%u (C++11) — writes the weekday as a decimal number, where Monday is 1 (ISO 8601 format) (range [1-7]). (field: tm_wday)
%Ou (C++11) — writes the weekday, where Monday is 1, using the alternative numeric system, e.g. 二 instead of 2 in the ja_JP locale. (field: tm_wday)

⭐ Hour, minute, second

%H — writes the hour as a decimal number, 24 hour clock (range [00-23]). (field: tm_hour)
%OH (C++11) — writes the hour from the 24-hour clock using the alternative numeric system, e.g. 十八 instead of 18 in the ja_JP locale. (field: tm_hour)
%I — writes the hour as a decimal number, 12 hour clock (range [01,12]). (field: tm_hour)
%OI (C++11) — writes the hour from the 12-hour clock using the alternative numeric system, e.g. 六 instead of 06 in the ja_JP locale. (field: tm_hour)
%M — writes the minute as a decimal number (range [00,59]). (field: tm_min)
%OM (C++11) — writes the minute using the alternative numeric system, e.g. 二十五 instead of 25 in the ja_JP locale. (field: tm_min)
%S — writes the second as a decimal number (range [00,60]). (field: tm_sec)
%OS (C++11) — writes the second using the alternative numeric system, e.g. 二十四 instead of 24 in the ja_JP locale. (field: tm_sec)

🫶 Other

%c — writes the standard date and time string, e.g. Sun Oct 17 04:41:13 2010 (locale dependent). (fields: all)
%Ec (C++11) — writes the alternative date and time string, e.g. using 平成23年 (year Heisei 23) instead of 2011年 (year 2011) in the ja_JP locale. (fields: all)
%x — writes the localized date representation (locale dependent). (fields: all)
%Ex (C++11) — writes the alternative date representation, e.g. using 平成23年 (year Heisei 23) instead of 2011年 (year 2011) in the ja_JP locale. (fields: all)
%X — writes the localized time representation, e.g. 18:40:20 or 6:40:20 PM (locale dependent). (fields: all)
%EX (C++11) — writes the alternative time representation (locale dependent). (fields: all)
%D (C++11) — equivalent to "%m/%d/%y". (fields: tm_mon, tm_mday, tm_year)
%F (C++11) — equivalent to "%Y-%m-%d" (the ISO 8601 date format). (fields: tm_mon, tm_mday, tm_year)
%r (C++11) — writes the localized 12-hour clock time (locale dependent). (fields: tm_hour, tm_min, tm_sec)
%R (C++11) — equivalent to "%H:%M". (fields: tm_hour, tm_min)
%T (C++11) — equivalent to "%H:%M:%S" (the ISO 8601 time format). (fields: tm_hour, tm_min, tm_sec)
%p — writes the localized a.m. or p.m. (locale dependent). (field: tm_hour)
%z (C++11) — writes the offset from UTC in the ISO 8601 format (e.g. -0430), or no characters if the time zone information is not available. (field: tm_isdst)
%Z — writes the locale-dependent time zone name or abbreviation, or no characters if the time zone information is not available. (field: tm_isdst)

🫶 RETURN VALUE 🫶

On success, you get the number of bytes written into the character array pointed to by str, not including the terminating '\0'.

⚠️ but bestie listen — if count was reached before the entire string could be stored, 0 is returned and the contents are indeterminate. So like, don't trust whatever's in that buffer afterward, fr fr 😭

(part 2 incoming, don't go anywhere 💅)

🎀 Example 🎀

okay bestie, this example is giving main-character energy, and here's the code exactly as the page shows it — no cap, no edits 💅

       // Run this code

        #include <ctime>
        #include <iostream>
        #include <iterator>
        #include <locale>

        void utcExample()
        {
            // Example of the very popular RFC 3339 format UTC time
            std::time_t time = std::time({});
            char timeString[std::size("yyyy-mm-ddThh:mm:ssZ")];
            std::strftime(std::data(timeString), std::size(timeString),
                          "%FT%TZ", std::gmtime(&time));
            std::cout << timeString << '\n';
        }

        int main()
        {
            std::time_t t = std::time(nullptr);
            char mbstr[100];

            if (std::strftime(mbstr, sizeof(mbstr), "%A %c",
       std::localtime(&t)))
                std::cout << mbstr << '\n';

            std::locale::global(std::locale("ja_JP.utf8"));
            if (std::strftime(mbstr, sizeof(mbstr), "%A %c",
       std::localtime(&t)))
                std::cout << mbstr << '\n';

            utcExample();
        }

🌸 Possible output 🌸

and the possible output is literally this, spacing and all:

        Tuesday Tue Sep  7 19:40:35 2021
        火曜日 2021年09月07日 19時40分35秒
        2021-09-07T19:40:35Z

💜 See also 💜

asctime — converts a std::tm object to a textual representation (function)
ctime — converts a std::time_t object to a textual representation (function)
wcsftime — converts a std::tm object to custom wide string textual representation (function)
put_time (C++11) — formats and outputs a date/time value according to the specified format (function template)
std::formatter<std::chrono::hh_mm_ss> (C++20) — formatting support for hh_mm_ss (class template specialization)
C documentation for strftime

footer tea, served cute: source is http://cppreference.com, version/date is 2024.06.10, and the page is std::strftime(3) — mwah, bestie 💋✨

📦 where this page comes from

nixpkgs unstable: stdman 2024.07.05
opensuse-leap 16.0: stdman 2024.07.05-bp160.1.9 · MIT
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on 2026-11-04: a language model's rewrite of the original, under its terms