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 4 digit decimal number | 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 IS0 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 IS0 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 | 
| h(C99)
 | synonym of b | tm_mon | 
| B | writes full month name, e.g. October(locale dependent) | 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 IS0 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 23 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 (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 time zone name or abbreviation, or no characters if the time zone information is not available (locale dependent) | tm_isdst |