# strftime

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< c‎ | chrono

Defined in header `<time.h>` |  |
size_t strftime( char* str, size_t count, const char* format, const struct tm* tp ); |  | (until C99)
size_t strftime( char* restrict str, size_t count, const char* restrict format, const struct tm* restrict tp ); |  | (since C99)

Converts the date and time information from a given calendar time tp to a null-terminated multibyte character string str according to format string format. Up to count bytes are written.

### Parameters

str | - | pointer to the first element of the char array for output
count | - | maximum number of bytes to write
format | - | pointer to a null-terminated multibyte character string specifying the format of conversion
tp | - | pointer to a struct tm object specifying the time to format

### Format string

The format string consists of zero or more conversion specifiers and ordinary characters (except `%`). All ordinary characters, including the terminating null character, are copied to the output string without modification. Each conversion specification begins with `%` character, optionally followed by `E` or `O` modifier (ignored if unsupported by the locale), followed by the character that determines the behavior of the specifier. The following format specifiers are available:

Conversion specifier | Explanation | Used fields
--- | --- | ---
`%` | writes literal `%`. The full conversion specification must be `%%`. |
`n` (C99) | writes newline character |
`t` (C99) | writes horizontal tab character |
Year
`Y` | writes year as a decimal number, e.g. 2017 | `tm_year`
`EY` (C99) | writes year in the alternative representation, e.g.平成23年 (year Heisei 23) instead of 2011年 (year 2011) in ja_JP locale | `tm_year`
`y` | writes last 2 digits of year as a decimal number (range `[00,99]`) | `tm_year`
`Oy` (C99) | writes last 2 digits of year using the alternative numeric system, e.g. 十一 instead of 11 in ja_JP locale | `tm_year`
`Ey` (C99) | writes year as offset from locale's alternative calendar period `%EC` (locale-dependent) | `tm_year`
`C` (C99) | writes first 2 digits of year as a decimal number (range `[00,99]`) | `tm_year`
`EC` (C99) | writes name of the base year (period) in the locale's alternative representation, e.g. 平成 (Heisei era) in ja_JP | `tm_year`
`G` (C99) | writes ISO 8601 week-based year, i.e. the year that contains the specified week. 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 | `tm_year`, `tm_wday`, `tm_yday`
`g` (C99) | writes last 2 digits of ISO 8601 week-based year, i.e. the year that contains the specified week (range `[00,99]`). 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 | `tm_year`, `tm_wday`, `tm_yday`
Month
`b` | writes abbreviated month name, e.g. `Oct` (locale dependent) | `tm_mon`
`Ob` (C23) | writes abbreviated month name in the locale's alternative representation | `tm_mon`
`h` (C99) | synonym of `b` | `tm_mon`
`B` | writes full month name, e.g. `October` (locale dependent) | `tm_mon`
`OB` (C23) | writes appropriate full month name in the locale's alternative representation | `tm_mon`
`m` | writes month as a decimal number (range `[01,12]`) | `tm_mon`
`Om` (C99) | writes month using the alternative numeric system, e.g. 十二 instead of 12 in ja_JP locale | `tm_mon`
Week
`U` | writes week of the year as a decimal number (Sunday is the first day of the week) (range `[00,53]`) | `tm_year`, `tm_wday`, `tm_yday`
`OU` (C99) | writes week of the year, as by `%U`, using the alternative numeric system, e.g. 五十二 instead of 52 in ja_JP locale | `tm_year`, `tm_wday`, `tm_yday`
`W` | writes week of the year as a decimal number (Monday is the first day of the week) (range `[00,53]`) | `tm_year`, `tm_wday`, `tm_yday`
`OW` (C99) | writes week of the year, as by `%W`, using the alternative numeric system, e.g. 五十二 instead of 52 in ja_JP locale | `tm_year`, `tm_wday`, `tm_yday`
`V` (C99) | writes ISO 8601 week of the year (range `[01,53]`). 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 | `tm_year`, `tm_wday`, `tm_yday`
`OV` (C99) | writes week of the year, as by `%V`, using the alternative numeric system, e.g. 五十二 instead of 52 in ja_JP locale | `tm_year`, `tm_wday`, `tm_yday`
Day of the year/month
`j` | writes day of the year as a decimal number (range `[001,366]`) | `tm_yday`
`d` | writes day of the month as a decimal number (range `[01,31]`) | `tm_mday`
`Od` (C99) | writes zero-based day of the month using the alternative numeric system, e.g. 二十七 instead of 27 in ja_JP locale Single character is preceded by a space. | `tm_mday`
`e` (C99) | writes day of the month as a decimal number (range `[1,31]`). Single digit is preceded by a space. | `tm_mday`
`Oe` (C99) | writes one-based day of the month using the alternative numeric system, e.g. 二十七 instead of 27 in ja_JP locale Single character is preceded by a space. | `tm_mday`
Day of the week
`a` | writes abbreviated weekday name, e.g. `Fri` (locale dependent) | `tm_wday`
`A` | writes full weekday name, e.g. `Friday` (locale dependent) | `tm_wday`
`w` | writes weekday as a decimal number, where Sunday is `0` (range `[0-6]`) | `tm_wday`
`Ow` (C99) | writes weekday, where Sunday is `0`, using the alternative numeric system, e.g. 二 instead of 2 in ja_JP locale | `tm_wday`
`u` (C99) | writes weekday as a decimal number, where Monday is `1` (ISO 8601 format) (range `[1-7]`) | `tm_wday`
`Ou` (C99) | writes weekday, where Monday is `1`, using the alternative numeric system, e.g. 二 instead of 2 in ja_JP locale | `tm_wday`
Hour, minute, second
`H` | writes hour as a decimal number, 24 hour clock (range `[00-23]`) | `tm_hour`
`OH` (C99) | writes hour from 24-hour clock using the alternative numeric system, e.g. 十八 instead of 18 in ja_JP locale | `tm_hour`
`I` | writes hour as a decimal number, 12 hour clock (range `[01,12]`) | `tm_hour`
`OI` (C99) | writes hour from 12-hour clock using the alternative numeric system, e.g. 六 instead of 06 in ja_JP locale | `tm_hour`
`M` | writes minute as a decimal number (range `[00,59]`) | `tm_min`
`OM` (C99) | writes minute using the alternative numeric system, e.g. 二十五 instead of 25 in ja_JP locale | `tm_min`
`S` | writes second as a decimal number (range `[00,60]`) | `tm_sec`
`OS` (C99) | writes second using the alternative numeric system, e.g. 二十四 instead of 24 in ja_JP locale | `tm_sec`
Other
`c` | writes standard date and time string, e.g. `Sun Oct 17 04:41:13 2010` (locale dependent) | all
`Ec` (C99) | writes alternative date and time string, e.g. using 平成23年 (year Heisei 23) instead of 2011年 (year 2011) in ja_JP locale | all
`x` | writes localized date representation (locale dependent) | all
`Ex` (C99) | writes alternative date representation, e.g. using 平成23年 (year Heisei 23) instead of 2011年 (year 2011) in ja_JP locale | all
`X` | writes localized time representation, e.g. 18:40:20 or 6:40:20 PM (locale dependent) | all
`EX` (C99) | writes alternative time representation (locale dependent) | all
`D` (C99) | equivalent to "%m/%d/%y" | `tm_mon`, `tm_mday`, `tm_year`
`F` (C99) | equivalent to "%Y-%m-%d" (the ISO 8601 date format) | `tm_mon`, `tm_mday`, `tm_year`
`r` (C99) | writes localized 12-hour clock time (locale dependent) | `tm_hour`, `tm_min`, `tm_sec`
`R` (C99) | equivalent to "%H:%M" | `tm_hour`, `tm_min`
`T` (C99) | equivalent to "%H:%M:%S" (the ISO 8601 time format) | `tm_hour`, `tm_min`, `tm_sec`
`p` | writes localized a.m. or p.m. (locale dependent) | `tm_hour`
`z` (C99) | writes offset from UTC in the ISO 8601 format (e.g. `-0430`), or no characters if the time zone information is not available | `tm_isdst`
`Z` | writes locale-dependent time zone name or abbreviation, or no characters if the time zone information is not available | `tm_isdst`

### Return value

The number of bytes written into the character array pointed to by str not including the terminating '\0' on success. If count was reached before the entire string could be stored, ​0​ is returned and the contents are indeterminate.

### Example

Run this code

    #include <locale.h>
    #include <stdio.h>
    #include <time.h>

    int main(void)
    {
        char buff[70];
        struct tm my_time = { .tm_year=112, // = year 2012
                              .tm_mon=9,    // = 10th month
                              .tm_mday=9,   // = 9th day
                              .tm_hour=8,   // = 8 hours
                              .tm_min=10,   // = 10 minutes
                              .tm_sec=20    // = 20 secs
        };

        if (strftime(buff, sizeof buff, "%A %c", &my_time))
            puts(buff);
        else
            puts("strftime failed");

        setlocale(LC_TIME, "el_GR.utf8");

        if (strftime(buff, sizeof buff, "%A %c", &my_time))
            puts(buff);
        else
            puts("strftime failed");
    }

Possible output:

    Sunday Sun Oct  9 08:10:20 2012
    Κυριακή Κυρ 09 Οκτ 2012 08:10:20 πμ EST

### References

- C23 standard (ISO/IEC 9899:2023):

  - 7.27.3.5 The strftime function (p: TBD)

- C17 standard (ISO/IEC 9899:2018):

  - 7.27.3.5 The strftime function (p: 288-291)

- C11 standard (ISO/IEC 9899:2011):

  - 7.27.3.5 The strftime function (p: 394-397)

- C99 standard (ISO/IEC 9899:1999):

  - 7.23.3.5 The strftime function (p: 343-347)

- C89/C90 standard (ISO/IEC 9899:1990):

  - 4.12.3.5 The strftime function

### See also

asctime asctime_s (deprecated in C23)(C11) | converts a tm object to a textual representation (function)
ctime ctime_s (deprecated in C23)(C11) | converts a time_t object to a textual representation (function)
wcsftime (C95) | converts a tm object to custom wide string textual representation (function)

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