NAME

strftime() − convert date and time to string

SYNOPSIS

#include <time.h>

size_t strftime(

char *s,
size_t maxsize,
const char *format,
const struct tm *timeptr

);

DESCRIPTION

strftime() converts the contents of a tm structure (see ctime(3C)) to a formatted date and time string.

strftime() places characters into the array pointed to by s as controlled by the string pointed to by format. The format string consists of zero or more directives and ordinary characters.  A directive consists of a % character, an optional field width and precision specification, and a terminating character that determines the directive’s behavior.  All ordinary characters (including the terminating null character are copied unchanged into the array.  No more than maxsize characters are placed into the array.  Each directive is replaced by the appropriate characters as described in the following list.  The appropriate characters are determined by the program’s locale, by the values contained in the structure pointed to by timeptr, and by the TZ environment variable (see External Influences below). 

Directives

The following directives, shown without the optional field width and precision specification, are replaced by the indicated characters:

%a Locale’s abbreviated weekday name. 

%A Locale’s full weekday name. 

%b Locale’s abbreviated month name. 

%B Locale’s full month name. 

%c Locale’s appropriate date and time representation. 

%d Day of the month as a decimal number [01,31]. 

%E Locale’s combined Emperor/Era name and year. 

%H Hour (24-hour clock) as a decimal number [00,23]. 

%I Hour (12-hour clock) as a decimal number [01,12]. 

%j Day of the year as a decimal number [001,366]. 

%m Month as a decimal number [01,12]. 

%M Minute as a decimal number [00,59]. 

%n New-line character. 

%N Locale’s Emperor/Era name. 

%o Locale’s Emperor/Era year. 

%p Locale’s equivalent of either AM or PM. 

%S Second as a decimal number [00,61]. 

%t Tab character. 

%U Week number of the year (Sunday as the first day of the week) as a decimal number [00,53].  All days in a new year preceding the first Sunday are considered to be in week 0. 

%w Weekday as a decimal number [0(Sunday),6]. 

%W Week number of the year (Monday as the first day of the week) as a decimal number [00,53].  All days in a new year preceding the first Sunday are considered to be in week 0. 

%x Locale’s appropriate date representation. 

%X Locale’s appropriate time representation. 

%y Year without century as a decimal number [00,99]. 

%Y Year with century as a decimal number. 

%Z Time zone name (or by no characters if no time zone exists). 

%% %

The following directives are provided for backward compatibility with the directives supported by date(1) and the ctime(3C) functions. It is recommended that the directives above be used in preference to those below.

%D Date in usual U.S.  format (%m/%d/%y) (use %x instead). 

%F Locale’s full month name (use %B instead). 

%h Locale’s abbreviated month name (use %b instead). 

%r Time in 12-hour U.S.  format (%I:%M:%S [AM|PM]) (use %X instead). 

%T Time in 24-hour U.S.  format (%H:%M:%S) (use %X instead). 

%z Time zone name (or by no characters if no time zone exists) (use %Z instead). 

If a directive is not one of the above, the behavior is undefined. 

Field Width and Precision

An optional field width and precision specification can immediately follow the initial % of a directive in the following order:

[-|0]w the decimal digit string w specifies a minimum field width in which the result of the conversion is right- or left-justified.  It is right-justified (with space padding) by default.  If the optional flag ‘-’ is specified, it is left-justified with space padding on the right.  If the optional flag ‘0’ is specified, it is right-justified and padded with zeros on the left. 

.p the decimal digit string p specifies the minimum number of digits to appear for the d, H, I, j, m, M, o, S, U, w, W, y and Y directives, and the maximum number of characters to be used from the a, A, b, B, c, D, E, F, h, n, N, p, r, t, T, x, X, z, Z, and % directives.  In the first case, if a directive supplies fewer digits than specified by the precision, it will be expanded with leading zeros.  In the second case, if a directive supplies more characters than specified by the precision, excess characters will truncated on the right. 

If no field width or precision is specified for a d, H, I, m, M, S, U, W, y, or j directive, a default of .2 is used for all but j for which .3 is used. 

EXTERNAL INFLUENCES

Locale

The LC_TIME category determines the characters to be substituted for those directives described above as being from the locale. 

The LC_CTYPE category determines the interpretation of the bytes within format as single and/or multi-byte characters. 

The LC_NUMERIC category determines the characters used to form numbers for those directives that produce numbers in the output.  If ALT_DIGITS (see langinfo(5)) is defined for the locale, the characters so specified are used in place of the default ASCII characters. 

Environment Variables

TZ determines the time zone name substituted for the %Z and %z directives.  The time zone name is determined by calling the function tzset() which sets the external variable tzname (see ctime(3C)).

International Code Set Support

Single- and multi-byte character code sets are supported. 

RETURN VALUE

If the total number of resulting characters including the terminating null character is not more than maxsize, strftime() returns the number of characters placed into the array pointed to by s, not including the terminating null character. Otherwise, zero is returned and the contents of the array are indeterminate.

EXAMPLES

If the timeptr argument contains the following values:

timeptr→tm_sec = 4;
timeptr→tm_min = 9;
timeptr→tm_hour = 15;
timeptr→tm_mday = 4;
timeptr→tm_mon = 6;
timeptr→tm_year = 88;
timeptr→tm_wday = 1;
timeptr→tm_yday = 185;
timeptr→tm_isdst = 1;

the following combinations of the LC_TIME category and format strings produce the indicated output:

† The directives used in these examples are not affected by the LC_TIME category of the locale. 

WARNINGS

If the arguments s and format are defined such that they overlap, the behavior is undefined. 

The function tzset() is called upon every invocation of strftime() (whether or not the time zone name is copied to the output array). 

The range of values for %S ([0,61]) extends to 61 to allow for the occasional one or two leap seconds.  However, the system does not accumulate leap seconds and the tm structure generated by the functions localtime() and gmtime() (see ctime(3C)) never reflects any leap seconds.

Results are undefined if values contained in the structure pointed to by timeptr exceed the ranges defined for the tm structure (see ctime(3C)) or are not consistent (such as if the tm_yday element is set to 0, indicating the first day of January, while the tm_mon element is set to 11, indicating a day in December). 

AUTHOR

strftime() was developed by HP. 

SEE ALSO

date(1), ctime(3C), getdate(3C), setlocale(3C), environ(5), langinfo(5), hpnls(5). 

STANDARDS CONFORMANCE

strftime(): AES, XPG3, XPG4, FIPS 151-2, POSIX.1, ANSI C

Hewlett-Packard Company  —  HP-UX Release 9.0: August 1992