NAME strftime - convert date and time to a string SYNOPSIS #include size_t strftime(char *restrict s, size_t maxsize, const char *restrict format, const struct tm *restrict timeptr); DESCRIPTION The strftime() function shall place bytes into the array pointed to by s as controlled by the string pointed to by format. The format is a character string, beginning and ending in its initial shift state, if any. The format string consists of zero or more conversion specifica- tions and ordinary characters. A conversion specification consists of a ā%ā character, possibly followed by an E or O modifier, and a termi- nating conversion specifier character that determines the conversion specificationās behavior. All ordinary characters (including the ter- minating null byte) are copied unchanged into the array. If copying takes place between objects that overlap, the behavior is undefined. No more than maxsize bytes are placed into the array. Each conversion specifier is replaced by appropriate characters as described in the following list. The appropriate characters are determined using the LC_TIME category of the current locale and by the values of zero or more members of the broken-down time structure pointed to by timeptr, as specified in brackets in the description. If any of the specified values are outside the normal range, the characters stored are unspec- ified. Local timezone information is used as though strftime() called tzset(). The following conversion specifications are supported: %a Replaced by the localeās abbreviated weekday name. [ tm_wday] %A Replaced by the localeās full weekday name. [ tm_wday] %b Replaced by the localeās abbreviated month name. [ tm_mon] %B Replaced by the localeās full month name. [ tm_mon] %c Replaced by the localeās appropriate date and time representa- tion. (See the Base Definitions volume of IEEE Std 1003.1-2001, .) %C Replaced by the year divided by 100 and truncated to an inte- ger, as a decimal number [00,99]. [ tm_year] %d Replaced by the day of the month as a decimal number [01,31]. [ tm_mday] %D Equivalent to %m / %d / %y . [ tm_mon, tm_mday, tm_year] %e Replaced by the day of the month as a decimal number [1,31]; a single digit is preceded by a space. [ tm_mday] %F Equivalent to %Y - %m - %d (the ISO 8601:2000 standard date format). [ tm_year, tm_mon, tm_mday] %g Replaced by the last 2 digits of the week-based year (see below) as a decimal number [00,99]. [ tm_year, tm_wday, tm_yday] %G Replaced by the week-based year (see below) as a decimal number (for example, 1977). [ tm_year, tm_wday, tm_yday] %h Equivalent to %b . [ tm_mon] %H Replaced by the hour (24-hour clock) as a decimal number [00,23]. [ tm_hour] %I Replaced by the hour (12-hour clock) as a decimal number [01,12]. [ tm_hour] %j Replaced by the day of the year as a decimal number [001,366]. [ tm_yday] %m Replaced by the month as a decimal number [01,12]. [ tm_mon] %M Replaced by the minute as a decimal number [00,59]. [ tm_min] %n Replaced by a . %p Replaced by the localeās equivalent of either a.m. or p.m. [ tm_hour] %r Replaced by the time in a.m. and p.m. notation; in the POSIX locale this shall be equivalent to %I : %M : %S %p . [ tm_hour, tm_min, tm_sec] %R Replaced by the time in 24-hour notation ( %H : %M ). [ tm_hour, tm_min] %S Replaced by the second as a decimal number [00,60]. [ tm_sec] %t Replaced by a . %T Replaced by the time ( %H : %M : %S ). [ tm_hour, tm_min, tm_sec] %u Replaced by the weekday as a decimal number [1,7], with 1 rep- resenting Monday. [ tm_wday] %U Replaced by the week number of the year as a decimal number [00,53]. The first Sunday of January is the first day of week 1; days in the new year before this are in week 0. [ tm_year, tm_wday, tm_yday] %V Replaced by the week number of the year (Monday as the first day of the week) as a decimal number [01,53]. If the week con- taining 1 January has four or more days in the new year, then it is considered week 1. Otherwise, it is the last week of the previous year, and the next week is week 1. Both January 4th and the first Thursday of January are always in week 1. [ tm_year, tm_wday, tm_yday] %w Replaced by the weekday as a decimal number [0,6], with 0 rep- resenting Sunday. [ tm_wday] %W Replaced by the week number of the year as a decimal number [00,53]. The first Monday of January is the first day of week 1; days in the new year before this are in week 0. [ tm_year, tm_wday, tm_yday] %x Replaced by the localeās appropriate date representation. (See the Base Definitions volume of IEEE Std 1003.1-2001, .) %X Replaced by the localeās appropriate time representation. (See the Base Definitions volume of IEEE Std 1003.1-2001, .) %y Replaced by the last two digits of the year as a decimal number [00,99]. [ tm_year] %Y Replaced by the year as a decimal number (for example, 1997). [ tm_year] %z Replaced by the offset from UTC in the ISO 8601:2000 standard format ( +hhmm or -hhmm ), or by no characters if no timezone is determinable. For example, "-0430" means 4 hours 30 minutes behind UTC (west of Greenwich). If tm_isdst is zero, the standard time offset is used. If tm_isdst is greater than zero, the daylight savings time offset is used. If tm_isdst is nega- tive, no characters are returned. [ tm_isdst] %Z Replaced by the timezone name or abbreviation, or by no bytes if no timezone information exists. [ tm_isdst] %% Replaced by % . If a conversion specification does not correspond to any of the above, the behavior is undefined. If a struct tm broken-down time structure is created by localtime() or localtime_r(), or modified by mktime(), and the value of TZ is subse- quently modified, the results of the %Z and %z strftime() conversion specifiers are undefined, when strftime() is called with such a bro- ken-down time structure. If a struct tm broken-down time structure is created or modified by gmtime() or gmtime_r(), it is unspecified whether the result of the %Z and %z conversion specifiers shall refer to UTC or the current local timezone, when strftime() is called with such a broken-down time structure. Modified Conversion Specifiers Some conversion specifiers can be modified by the E or O modifier characters to indicate that an alternative format or specification should be used rather than the one normally used by the unmodified conversion specifier. If the alternative format or specification does not exist for the current locale (see ERA in the Base Definitions vol- ume of IEEE Std 1003.1-2001, Section 7.3.5, LC_TIME), the behavior shall be as if the unmodified conversion specification were used. %Ec Replaced by the localeās alternative appropriate date and time representation. %EC Replaced by the name of the base year (period) in the localeās alternative representation. %Ex Replaced by the localeās alternative date representation. %EX Replaced by the localeās alternative time representation. %Ey Replaced by the offset from %EC (year only) in the localeās alternative representation. %EY Replaced by the full alternative year representation. %Od Replaced by the day of the month, using the localeās alterna- tive numeric symbols, filled as needed with leading zeros if there is any alternative symbol for zero; otherwise, with lead- ing spaces. %Oe Replaced by the day of the month, using the localeās alterna- tive numeric symbols, filled as needed with leading spaces. %OH Replaced by the hour (24-hour clock) using the localeās alter- native numeric symbols. %OI Replaced by the hour (12-hour clock) using the localeās alter- native numeric symbols. %Om Replaced by the month using the localeās alternative numeric symbols. %OM Replaced by the minutes using the localeās alternative numeric symbols. %OS Replaced by the seconds using the localeās alternative numeric symbols. %Ou Replaced by the weekday as a number in the localeās alternative representation (Monday=1). %OU Replaced by the week number of the year (Sunday as the first day of the week, rules corresponding to %U ) using the localeās alternative numeric symbols. %OV Replaced by the week number of the year (Monday as the first day of the week, rules corresponding to %V ) using the localeās alternative numeric symbols. %Ow Replaced by the number of the weekday (Sunday=0) using the localeās alternative numeric symbols. %OW Replaced by the week number of the year (Monday as the first day of the week) using the localeās alternative numeric sym- bols. %Oy Replaced by the year (offset from %C ) using the localeās alternative numeric symbols. %g , %G , and %V give values according to the ISO 8601:2000 standard week-based year. In this system, weeks begin on a Monday and week 1 of the year is the week that includes January 4th, which is also the week that includes the first Thursday of the year, and is also the first week that contains at least four days in the year. If the first Monday of January is the 2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus, for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and %V is replaced by 01. If a conversion specifier is not one of the above, the behavior is undefined. RETURN VALUE If the total number of resulting bytes including the terminating null byte is not more than maxsize, strftime() shall return the number of bytes placed into the array pointed to by s, not including the termi- nating null byte. Otherwise, 0 shall be returned and the contents of the array are unspecified. ERRORS No errors are defined. COPYRIGHT Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .