1STRFTIME(3P) POSIX Programmer's Manual STRFTIME(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 strftime - convert date and time to a string
13
15 #include <time.h>
16 size_t strftime(char *restrict s, size_t maxsize,
18 const char *restrict format, const struct tm *restrict timeptr);
19
22 The strftime() function shall place bytes into the array pointed to by
23 s as controlled by the string pointed to by format. The format is a
24 character string, beginning and ending in its initial shift state, if
25 any. The format string consists of zero or more conversion specifica‐
26 tions and ordinary characters. A conversion specification consists of
27 a '%' character, possibly followed by an E or O modifier, and a termi‐
28 nating conversion specifier character that determines the conversion
29 specification's behavior. All ordinary characters (including the termi‐
30 nating null byte) are copied unchanged into the array. If copying takes
31 place between objects that overlap, the behavior is undefined. No more
32 than maxsize bytes are placed into the array. Each conversion specifier
33 is replaced by appropriate characters as described in the following
34 list. The appropriate characters are determined using the LC_TIME cate‐
35 gory of the current locale and by the values of zero or more members of
36 the broken-down time structure pointed to by timeptr, as specified in
37 brackets in the description. If any of the specified values are outside
38 the normal range, the characters stored are unspecified.
39 Local timezone information is used as though strftime() called tzset().
41 The following conversion specifications are supported:
43 %a Replaced by the locale's abbreviated weekday name. [ tm_wday]
45 %A Replaced by the locale's full weekday name. [ tm_wday]
47 %b Replaced by the locale's abbreviated month name. [ tm_mon]
49 %B Replaced by the locale's full month name. [ tm_mon]
51 %c Replaced by the locale's appropriate date and time representa‐
53 tion. (See the Base Definitions volume of IEEE Std 1003.1-2001,
54 <time.h>.)
55 %C Replaced by the year divided by 100 and truncated to an integer,
57 as a decimal number [00,99]. [ tm_year]
58 %d Replaced by the day of the month as a decimal number [01,31]. [
60 tm_mday]
61 %D Equivalent to %m / %d / %y . [ tm_mon, tm_mday, tm_year]
63 %e Replaced by the day of the month as a decimal number [1,31]; a
65 single digit is preceded by a space. [ tm_mday]
66 %F Equivalent to %Y - %m - %d (the ISO 8601:2000 standard date for‐
68 mat). [ tm_year, tm_mon, tm_mday]
69 %g Replaced by the last 2 digits of the week-based year (see below)
71 as a decimal number [00,99]. [ tm_year, tm_wday, tm_yday]
72 %G Replaced by the week-based year (see below) as a decimal number
74 (for example, 1977). [ tm_year, tm_wday, tm_yday]
75 %h Equivalent to %b . [ tm_mon]
77 %H Replaced by the hour (24-hour clock) as a decimal number
79 [00,23]. [ tm_hour]
80 %I Replaced by the hour (12-hour clock) as a decimal number
82 [01,12]. [ tm_hour]
83 %j Replaced by the day of the year as a decimal number [001,366]. [
85 tm_yday]
86 %m Replaced by the month as a decimal number [01,12]. [ tm_mon]
88 %M Replaced by the minute as a decimal number [00,59]. [ tm_min]
90 %n Replaced by a <newline>.
92 %p Replaced by the locale's equivalent of either a.m. or p.m. [
94 tm_hour]
95 %r Replaced by the time in a.m. and p.m. notation; in the POSIX
97 locale this shall be equivalent to %I : %M : %S %p . [ tm_hour,
98 tm_min, tm_sec]
99 %R Replaced by the time in 24-hour notation ( %H : %M ). [
101 tm_hour, tm_min]
102 %S Replaced by the second as a decimal number [00,60]. [ tm_sec]
104 %t Replaced by a <tab>.
106 %T Replaced by the time ( %H : %M : %S ). [ tm_hour, tm_min,
108 tm_sec]
109 %u Replaced by the weekday as a decimal number [1,7], with 1 repre‐
111 senting Monday. [ tm_wday]
112 %U Replaced by the week number of the year as a decimal number
114 [00,53]. The first Sunday of January is the first day of week
115 1; days in the new year before this are in week 0. [ tm_year,
116 tm_wday, tm_yday]
117 %V Replaced by the week number of the year (Monday as the first day
119 of the week) as a decimal number [01,53]. If the week containing
120 1 January has four or more days in the new year, then it is con‐
121 sidered week 1. Otherwise, it is the last week of the previous
122 year, and the next week is week 1. Both January 4th and the
123 first Thursday of January are always in week 1. [ tm_year,
124 tm_wday, tm_yday]
125 %w Replaced by the weekday as a decimal number [0,6], with 0 repre‐
127 senting Sunday. [ tm_wday]
128 %W Replaced by the week number of the year as a decimal number
130 [00,53]. The first Monday of January is the first day of week
131 1; days in the new year before this are in week 0. [ tm_year,
132 tm_wday, tm_yday]
133 %x Replaced by the locale's appropriate date representation. (See
135 the Base Definitions volume of IEEE Std 1003.1-2001, <time.h>.)
136 %X Replaced by the locale's appropriate time representation. (See
138 the Base Definitions volume of IEEE Std 1003.1-2001, <time.h>.)
139 %y Replaced by the last two digits of the year as a decimal number
141 [00,99]. [ tm_year]
142 %Y Replaced by the year as a decimal number (for example, 1997). [
144 tm_year]
145 %z Replaced by the offset from UTC in the ISO 8601:2000 standard
147 format ( +hhmm or -hhmm ), or by no characters if no timezone is
148 determinable. For example, "-0430" means 4 hours 30 minutes
149 behind UTC (west of Greenwich). If tm_isdst is zero, the stan‐
150 dard time offset is used. If tm_isdst is greater than zero, the
151 daylight savings time offset is used. If tm_isdst is negative,
152 no characters are returned. [ tm_isdst]
153 %Z Replaced by the timezone name or abbreviation, or by no bytes if
155 no timezone information exists. [ tm_isdst]
156 %% Replaced by % .
158 If a conversion specification does not correspond to any of the above,
161 the behavior is undefined.
162 If a struct tm broken-down time structure is created by localtime() or
164 localtime_r(), or modified by mktime(), and the value of TZ is subse‐
165 quently modified, the results of the %Z and %z strftime() conversion
166 specifiers are undefined, when strftime() is called with such a broken-
167 down time structure.
168 If a struct tm broken-down time structure is created or modified by
170 gmtime() or gmtime_r(), it is unspecified whether the result of the %Z
171 and %z conversion specifiers shall refer to UTC or the current local
172 timezone, when strftime() is called with such a broken-down time struc‐
173 ture.
174 Modified Conversion Specifiers
176 Some conversion specifiers can be modified by the E or O modifier char‐
177 acters to indicate that an alternative format or specification should
178 be used rather than the one normally used by the unmodified conversion
179 specifier. If the alternative format or specification does not exist
180 for the current locale (see ERA in the Base Definitions volume of
181 IEEE Std 1003.1-2001, Section 7.3.5, LC_TIME), the behavior shall be as
182 if the unmodified conversion specification were used.
183 %Ec Replaced by the locale's alternative appropriate date and time
185 representation.
186 %EC Replaced by the name of the base year (period) in the locale's
188 alternative representation.
189 %Ex Replaced by the locale's alternative date representation.
191 %EX Replaced by the locale's alternative time representation.
193 %Ey Replaced by the offset from %EC (year only) in the locale's
195 alternative representation.
196 %EY Replaced by the full alternative year representation.
198 %Od Replaced by the day of the month, using the locale's alternative
200 numeric symbols, filled as needed with leading zeros if there is
201 any alternative symbol for zero; otherwise, with leading spaces.
202 %Oe Replaced by the day of the month, using the locale's alternative
204 numeric symbols, filled as needed with leading spaces.
205 %OH Replaced by the hour (24-hour clock) using the locale's alterna‐
207 tive numeric symbols.
208 %OI Replaced by the hour (12-hour clock) using the locale's alterna‐
210 tive numeric symbols.
211 %Om Replaced by the month using the locale's alternative numeric
213 symbols.
214 %OM Replaced by the minutes using the locale's alternative numeric
216 symbols.
217 %OS Replaced by the seconds using the locale's alternative numeric
219 symbols.
220 %Ou Replaced by the weekday as a number in the locale's alternative
222 representation (Monday=1).
223 %OU Replaced by the week number of the year (Sunday as the first day
225 of the week, rules corresponding to %U ) using the locale's
226 alternative numeric symbols.
227 %OV Replaced by the week number of the year (Monday as the first day
229 of the week, rules corresponding to %V ) using the locale's
230 alternative numeric symbols.
231 %Ow Replaced by the number of the weekday (Sunday=0) using the
233 locale's alternative numeric symbols.
234 %OW Replaced by the week number of the year (Monday as the first day
236 of the week) using the locale's alternative numeric symbols.
237 %Oy Replaced by the year (offset from %C ) using the locale's alter‐
239 native numeric symbols.
240 %g, %G, and %V give values according to the ISO 8601:2000 standard
243 week-based year. In this system, weeks begin on a Monday and week 1 of
244 the year is the week that includes January 4th, which is also the week
245 that includes the first Thursday of the year, and is also the first
246 week that contains at least four days in the year. If the first Monday
247 of January is the 2nd, 3rd, or 4th, the preceding days are part of the
248 last week of the preceding year; thus, for Saturday 2nd January 1999,
249 %G is replaced by 1998 and %V is replaced by 53. If December 29th,
250 30th, or 31st is a Monday, it and any following days are part of week 1
251 of the following year. Thus, for Tuesday 30th December 1997, %G is
252 replaced by 1998 and %V is replaced by 01.
253 If a conversion specifier is not one of the above, the behavior is
255 undefined.
256
258 If the total number of resulting bytes including the terminating null
259 byte is not more than maxsize, strftime() shall return the number of
260 bytes placed into the array pointed to by s, not including the termi‐
261 nating null byte. Otherwise, 0 shall be returned and the contents of
262 the array are unspecified.
263
265 No errors are defined.
266 The following sections are informative.
268
270 Getting a Localized Date String
271 The following example first sets the locale to the user's default. The
272 locale information will be used in the nl_langinfo() and strftime()
273 functions. The nl_langinfo() function returns the localized date string
274 which specifies how the date is laid out. The strftime() function takes
275 this information and, using the tm structure for values, places the
276 date and time information into datestring.
277 #include <time.h>
280 #include <locale.h>
281 #include <langinfo.h>
282 ...
283 struct tm *tm;
284 char datestring[256];
285 ...
286 setlocale (LC_ALL, "");
287 ...
288 strftime (datestring, sizeof(datestring), nl_langinfo (D_T_FMT), tm);
289 ...
290
292 The range of values for %S is [00,60] rather than [00,59] to allow for
293 the occasional leap second.
294 Some of the conversion specifications are duplicates of others. They
296 are included for compatibility with nl_cxtime() and nl_ascxtime(),
297 which were published in Issue 2.
298 Applications should use %Y (4-digit years) in preference to %y (2-digit
300 years).
301 In the C locale, the E and O modifiers are ignored and the replacement
303 strings for the following specifiers are:
304 %a The first three characters of %A .
306 %A One of Sunday, Monday, ..., Saturday.
308 %b The first three characters of %B .
310 %B One of January, February, ..., December.
312 %c Equivalent to %a %b %e %T %Y .
314 %p One of AM or PM.
316 %r Equivalent to %I : %M : %S %p .
318 %x Equivalent to %m / %d / %y .
320 %X Equivalent to %T .
322 %Z Implementation-defined.
324
327 None.
328
330 None.
331
333 asctime(), clock(), ctime(), difftime(), getdate(), gmtime(), local‐
334 time(), mktime(), strptime(), time(), tzset(), utime(), Base Defini‐
335 tions volume of IEEE Std 1003.1-2001, Section 7.3.5, LC_TIME, <time.h>
336
338 Portions of this text are reprinted and reproduced in electronic form
339 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
340 -- Portable Operating System Interface (POSIX), The Open Group Base
341 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
342 Electrical and Electronics Engineers, Inc and The Open Group. In the
343 event of any discrepancy between this version and the original IEEE and
344 The Open Group Standard, the original IEEE and The Open Group Standard
345 is the referee document. The original Standard can be obtained online
346 at http://www.opengroup.org/unix/online.html .
347IEEE/The Open Group 2003 STRFTIME(3P)