strftime

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< c‎ | chrono
 
C
 
Date and time utilities
Functions
Time manipulation
(C11)
(C23)
Format conversions
(C23)(C11)
(C23)(C11)
strftime
(C95)
(C23)(C11)
(C23)(C11)
Constants
Types
(C11)
 
Defined in header <time.h>
size_t strftime( char *         str, size_t count,
                 const char *         format, const struct tm *         time );
 (until C99)
size_t strftime( char *restrict str, size_t count,
                 const char *restrict format, const struct tm *restrict time );
 (since C99)

Converts the date and time information from a given calendar time time 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
time - 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 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
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 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 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 undefined.

Example

Run this code
#include <stdio.h>
#include <time.h>
#include <locale.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

  • 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

(C23)(C11)
 converts a tm object to a textual representation
(function)
(C23)(C11)
 converts a time_t object to a textual representation
(function)
(C95)
 converts a tm object to custom wide string textual representation
(function)
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