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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |ENVIRONMENT |ATTRIBUTES |STANDARDS |HISTORY |NOTES |BUGS |EXAMPLES |SEE ALSO |COLOPHON | |
strftime(3) Library Functions Manualstrftime(3)strftime - format date and time
Standard C library (libc,-lc)
#include <time.h>size_t strftime(size_t max;chars[restrictmax], size_tmax,const char *restrictformat,const struct tm *restricttm);size_t strftime_l(size_t max;chars[restrictmax], size_tmax,const char *restrictformat,const struct tm *restricttm,locale_tlocale);
Thestrftime() function formats the broken-down timetm according to the format specificationformat and places the result in the character arrays of sizemax. The broken-down time structuretm is defined in<time.h>. See alsoctime(3). The format specification is a null-terminated string and may contain special character sequences calledconversionspecifications, each of which is introduced by a '%' character and terminated by some other character known as aconversion specifiercharacter. All other character sequences areordinary charactersequences. The characters of ordinary character sequences (including the null byte) are copied verbatim fromformat tos. However, the characters of conversion specifications are replaced as shown in the list below. In this list, the field(s) employed from thetm structure are also shown.%aThe abbreviated name of the day of the week according to the current locale. (Calculated fromtm_wday.) (The specific names used in the current locale can be obtained by callingnl_langinfo(3) withABDAY_{1–7} as an argument.)%AThe full name of the day of the week according to the current locale. (Calculated fromtm_wday.) (The specific names used in the current locale can be obtained by callingnl_langinfo(3) withDAY_{1–7} as an argument.)%bThe abbreviated month name according to the current locale. (Calculated fromtm_mon.) (The specific names used in the current locale can be obtained by callingnl_langinfo(3) withABMON_{1–12} as an argument.)%BThe full month name according to the current locale. (Calculated fromtm_mon.) (The specific names used in the current locale can be obtained by callingnl_langinfo(3) withMON_{1–12} as an argument.)%cThe preferred date and time representation for the current locale. (The specific format used in the current locale can be obtained by callingnl_langinfo(3) withD_T_FMTas an argument for the%cconversion specification, and withERA_D_T_FMTfor the%Ecconversion specification.) (In the POSIX locale this is equivalent to%a %b %e %H:%M:%S %Y.)%CThe century number (year/100) as a 2-digit integer. (SU) (The%ECconversion specification corresponds to the name of the era.) (Calculated fromtm_year.)%dThe day of the month as a decimal number (range 01 to 31). (Calculated fromtm_mday.)%DEquivalent to%m/%d/%y. (Yecch—for Americans only. Americans should note that in other countries%d/%m/%yis rather common. This means that in international context this format is ambiguous and should not be used.) (SU)%eLike%d, the day of the month as a decimal number, but a leading zero is replaced by a space. (SU) (Calculated fromtm_mday.)%EModifier: use alternative ("era-based") format, see below. (SU)%FEquivalent to%Y-%m-%d(the ISO 8601 date format). (C99)%GThe ISO 8601 week-based year (see NOTES) with century as a decimal number. The 4-digit year corresponding to the ISO week number (see%V). This has the same format and value as%Y, except that if the ISO week number belongs to the previous or next year, that year is used instead. (TZ) (Calculated fromtm_year,tm_yday, andtm_wday.)%gLike%G, but without century, that is, with a 2-digit year (00–99). (TZ) (Calculated fromtm_year,tm_yday, andtm_wday.)%hEquivalent to%b. (SU)%HThe hour as a decimal number using a 24-hour clock (range 00 to 23). (Calculated fromtm_hour.)%IThe hour as a decimal number using a 12-hour clock (range 01 to 12). (Calculated fromtm_hour.)%jThe day of the year as a decimal number (range 001 to 366). (Calculated fromtm_yday.)%kThe hour (24-hour clock) as a decimal number (range 0 to 23); single digits are preceded by a blank. (See also%H.) (Calculated fromtm_hour.) (TZ)%lThe hour (12-hour clock) as a decimal number (range 1 to 12); single digits are preceded by a blank. (See also%I.) (Calculated fromtm_hour.) (TZ)%mThe month as a decimal number (range 01 to 12). (Calculated fromtm_mon.)%MThe minute as a decimal number (range 00 to 59). (Calculated fromtm_min.)%nA newline character. (SU)%OModifier: use alternative numeric symbols, see below. (SU)%pEither "AM" or "PM" according to the given time value, or the corresponding strings for the current locale. Noon is treated as "PM" and midnight as "AM". (Calculated fromtm_hour.) (The specific string representations used for "AM" and "PM" in the current locale can be obtained by callingnl_langinfo(3) withAM_STRandPM_STR, respectively.)%PLike%pbut in lowercase: "am" or "pm" or a corresponding string for the current locale. (Calculated fromtm_hour.) (GNU)%rThe time in a.m. or p.m. notation. (SU) (The specific format used in the current locale can be obtained by callingnl_langinfo(3) withT_FMT_AMPMas an argument.) (In the POSIX locale this is equivalent to%I:%M:%S %p.)%RThe time in 24-hour notation (%H:%M). (SU) For a version including the seconds, see%Tbelow.%sThe number of seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC). (TZ) (Calculated frommktime(tm).)%SThe second as a decimal number (range 00 to 60). (The range is up to 60 to allow for occasional leap seconds.) (Calculated fromtm_sec.)%tA tab character. (SU)%TThe time in 24-hour notation (%H:%M:%S). (SU)%uThe day of the week as a decimal, range 1 to 7, Monday being 1. See also%w. (Calculated fromtm_wday.) (SU)%UThe week number of the current year as a decimal number, range 00 to 53, starting with the first Sunday as the first day of week 01. See also%Vand%W. (Calculated fromtm_yday andtm_wday.)%VThe ISO 8601 week number (see NOTES) of the current year as a decimal number, range 01 to 53, where week 1 is the first week that has at least 4 days in the new year. See also%U and%W. (Calculated fromtm_year,tm_yday, andtm_wday.) (SU)%wThe day of the week as a decimal, range 0 to 6, Sunday being 0. See also%u. (Calculated fromtm_wday.)%WThe week number of the current year as a decimal number, range 00 to 53, starting with the first Monday as the first day of week 01. (Calculated fromtm_yday andtm_wday.)%xThe preferred date representation for the current locale without the time. (The specific format used in the current locale can be obtained by callingnl_langinfo(3) withD_FMT as an argument for the%xconversion specification, and withERA_D_FMTfor the%Exconversion specification.) (In the POSIX locale this is equivalent to%m/%d/%y.)%XThe preferred time representation for the current locale without the date. (The specific format used in the current locale can be obtained by callingnl_langinfo(3) withT_FMT as an argument for the%Xconversion specification, and withERA_T_FMTfor the%EXconversion specification.) (In the POSIX locale this is equivalent to%H:%M:%S.)%yThe year as a decimal number without a century (range 00 to 99). (The%Eyconversion specification corresponds to the year since the beginning of the era denoted by the%EC conversion specification.) (Calculated fromtm_year)%YThe year as a decimal number including the century. (The%EYconversion specification corresponds to the full alternative year representation.) (Calculated fromtm_year)%zThe+hhmm or-hhmm numeric timezone (that is, the hour and minute offset from UTC). (SU)%ZThe timezone name or abbreviation.%+The date and time indate(1) format. (TZ) (Not supported in glibc2.)%%A literal '%' character. Some conversion specifications can be modified by preceding the conversion specifier character by theEorOmodifier to indicate that an alternative format should be used. If the alternative format or specification does not exist for the current locale, the behavior will be as if the unmodified conversion specification were used. (SU) The Single UNIX Specification mentions%Ec,%EC,%Ex,%EX,%Ey,%EY,%Od,%Oe,%OH,%OI,%Om,%OM,%OS,%Ou,%OU,%OV,%Ow,%OW,%Oy, where the effect of theOmodifier is to use alternative numeric symbols (say, roman numerals), and that of theEmodifier is to use a locale-dependent alternative representation. The rules governing date representation with theEmodifier can be obtained by supplyingERAas an argument to anl_langinfo(3). One example of such alternative forms is the Japanese era calendar scheme in theja_JPglibc locale.strftime_l() is equivalent tostrftime(), except it uses the specifiedlocale instead of the current locale. The behaviour is undefined iflocale is invalid orLC_GLOBAL_LOCALE.Provided that the result string, including the terminating null byte, does not exceedmax bytes,strftime() returns the number of bytes (excluding the terminating null byte) placed in the arrays. If the length of the result string (including the terminating null byte) would exceedmax bytes, thenstrftime() returns 0, and the contents of the array are undefined. Note that the return value 0 does not necessarily indicate an error. For example, in many locales%pyields an empty string. An emptyformat string will likewise yield an empty string.
The environment variablesTZandLC_TIMEare used.
For an explanation of the terms used in this section, seeattributes(7). ┌───────────────────────────┬───────────────┬────────────────────┐ │Interface│Attribute│Value│ ├───────────────────────────┼───────────────┼────────────────────┤ │strftime(),strftime_l() │ Thread safety │ MT-Safe env locale │ └───────────────────────────┴───────────────┴────────────────────┘
strftime() C11, POSIX.1-2008.strftime_l() POSIX.1-2008.
strftime() SVr4, C89.strftime_l() POSIX.1-2008. There are strict inclusions between the set of conversions given in ANSI C (unmarked), those given in the Single UNIX Specification (marked SU), those given in Olson's timezone package (marked TZ), and those given in glibc (marked GNU), except that%+is not supported in glibc2. On the other hand glibc2 has several more extensions. POSIX.1 only refers to ANSI C; POSIX.2 describes underdate(1) several extensions that could apply tostrftime() as well. The%Fconversion is in C99 and POSIX.1-2001. In SUSv2, the%Sspecifier allowed a range of 00 to 61, to allow for the theoretical possibility of a minute that included a double leap second (there never has been such a minute).
ISO 8601 week dates%G,%g, and%Vyield values calculated from the week-based year defined by the ISO 8601 standard. In this system, weeks start on a Monday, and are numbered from 01, for the first week, up to 52 or 53, for the last week. Week 1 is the first week where four or more days fall within the new year (or, synonymously, week 01 is: the first week of the year that contains a Thursday; or, the week that has 4 January in it). When three or fewer days of the first calendar week of the new year fall within that year, then the ISO 8601 week-based system counts those days as part of week 52 or 53 of the preceding year. For example, 1 January 2010 is a Friday, meaning that just three days of that calendar week fall in 2010. Thus, the ISO 8601 week-based system considers these days to be part of week 53 (%V) of the year 2009 (%G); week 01 of ISO 8601 year 2010 starts on Monday, 4 January 2010. Similarly, the first two days of January 2011 are considered to be part of week 52 of the year 2010.glibc notes glibc provides some extensions for conversion specifications. (These extensions are not specified in POSIX.1-2001, but a few other systems provide similar features.) Between the '%' character and the conversion specifier character, an optionalflag and fieldwidth may be specified. (These precede theEorO modifiers, if present.) The following flag characters are permitted:_(underscore) Pad a numeric result string with spaces.-(dash) Do not pad a numeric result string.0Pad a numeric result string with zeros even if the conversion specifier character uses space-padding by default.^Convert alphabetic characters in result string to uppercase.#Swap the case of the result string. (This flag works only with certain conversion specifier characters, and of these, it is only really useful with%Z.) An optional decimal width specifier may follow the (possibly absent) flag. If the natural size of the field is smaller than this width, then the result string is padded (on the left) to the specified width.
If the output string would exceedmax bytes,errno isnot set. This makes it impossible to distinguish this error case from cases where theformat string legitimately produces a zero-length output string. POSIX.1-2001 doesnot specify anyerrno settings forstrftime(). Some buggy versions ofgcc(1) complain about the use of%c:warning: `%c' yields only last 2 digits of year in some locales. Of course programmers are encouraged to use%c, as it gives the preferred date and time representation. One meets all kinds of strange obfuscations to circumvent thisgcc(1) problem. A relatively clean one is to add an intermediate function size_t my_strftime(char *s, size_t max, const char *fmt, const struct tm *tm) { return strftime(s, max, fmt, tm); } Nowadays,gcc(1) provides the-Wno-format-y2k option to prevent the warning, so that the above workaround is no longer required.RFC 2822-compliant date format(with an English locale for %a and %b) "%a, %d %b %Y %T %z"RFC 822-compliant date format(with an English locale for %a and %b) "%a, %d %b %y %T %z"Example program The program below can be used to experiment withstrftime(). Some examples of the result string produced by the glibc implementation ofstrftime() are as follows: $./a.out '%m' Result string is "11" $./a.out '%5m' Result string is "00011" $./a.out '%_5m' Result string is " 11"Program source #include <stdio.h> #include <stdlib.h> #include <time.h> int main(int argc, char *argv[]) { char outstr[200]; time_t t; struct tm *tmp; t = time(NULL); tmp = localtime(&t); if (tmp == NULL) { perror("localtime"); exit(EXIT_FAILURE); } if (strftime(outstr, sizeof(outstr), argv[1], tmp) == 0) { fprintf(stderr, "strftime returned 0"); exit(EXIT_FAILURE); } printf("Result string is \"%s\"\n", outstr); exit(EXIT_SUCCESS); }date(1),time(2),ctime(3),nl_langinfo(3),setlocale(3),sprintf(3),strptime(3)
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