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.L time_t values are the number of seconds since the epoch, "Jan 1 00:00:00 GMT 1970" , with leap seconds omitted.
The global variable .L "int tm_info.flags" contains flags that allow all programs using the library to be controlled in a consistent manner. .L tm_info.flags is initialized by the .L tminit() routine described below, and may be explicitly reset after .L tminit() is called. The flags are:
.L TM_ADJUST Set by .L tminit() if .L localtime() and .L gmtime() do not compensate for leap seconds.
.L TM_LEAP .L time_t values are interpreted as if they include leap seconds. Set by .L tminit() if the .L leap option is set in the .L TM_OPTIONS environment variable.
.L TM_UTC Times are relative to UTC (universal coordinated time, i.e., GMT ). Otherwise times are relative to the local time zone. Set by .L tminit() if the time zone name matches one of .L tm_info.format[43] through .L tm_info.format[46] described below. If the time zone name is not determined by .L localtime() then the environment variables .L TZNAME (as described in BSD 4.3) and .L TZ (as described in System V) are checked, in order. If this fails then the time zone name is constructed using the local time zone offset.
The routines are:
.L "time_t tmdate(const char* date, char** end, time_t* clock)" Parses the date specification .L date using the .L tm_info.format string table (described below) and returns the equivalent .L time_t value. If .RL non- NULL , .L end is set to the position of the first unrecognized character in .LR date . .L clock is used to provide default values for omitted components in .LR date . If .L clock is .L NULL then the current time is used.
.L "struct tm* tmfix(struct tm* tp)" Corrects any out of bounds fields in .L tp and returns .L tp as its value. The corrections start with .L tp->tm_sec and propagate down to .LR tp->tm_year . For example, if .L tp->tm_sec were 61 then it would change to 1 and .L tp->tm_min would be incremented by 1, and so on. .LR tp->tm_wday , .LR tp->tm_yday and .L tp->tm_isdst are not changed as these can be computed from the other fields.
.L "char* tmfmt(char* buf, size_t len, const char* format, time_t* clock)" Formats the date pointed to by .L clock into the buffer .L buf with size .L len bytes according to the format specification .LR format . If .L format is .L NULL or empty then the string .L tm_info.format[40] is used. If .L clock is .L NULL then the current time is used. A pointer to the end of .L buf (i.e., the terminating .LR "'\e0'" ) is returned.
.L format is in the style of printf (3), where % field causes the corresponding fixed size field to be placed in .LR buf , zero padded if necessary, and \ec and \ennn sequences are interpreted as in the C language. Otherwise invalid % field specifications and all other characters in .L format are copied into .L buf without change. String field values are taken from the .L tm_info.format string table. The fields are:
0 % % character.
a Abbreviated weekday name.
A Full weekday name.
b Abbreviated month name.
c ctime (3) style date without the trailing newline .
C date (1) style date.
d Day of month number.
D Date as mm / dd / yy .
e Blank padded day of month number.
E Unpadded day of month number.
h Abbreviated month name.
H 24-hour clock hour.
i International date (1) date that includes the time zone type name.
I 12-hour clock hour.
j 1-offset Julian date.
J 0-offset Julian date.
l ls (1) -l date that lists recent dates with hh : mm and distant dates with yyyy .
m Month number.
M Minutes.
n newline character.
p Meridian (e.g., AM or PM ).
r 12-hour time as hh : mm : ss meridian .
R 24-hour time as hh : mm .
S Seconds.
t tab character.
T 24-hour time as hh : mm : ss .
U Week number with Sunday as the first day.
w Weekday number.
W Week number with Monday as the first day.
x Local date style, using .LR tm_info.format[39] , that includes the month, day and year.
X Local time style, using .LR tm_info.format[38] , that includes the hours and minutes.
y 2-digit year.
Y 4-digit year.
z Time zone type name.
Z Time zone name.
+ flag
- flag Temporarily (until .L tmform() returns) sets (+) or clears (-) the .L tm_info.flags flags specified by flag :
l .L TM_LEAP
u .L TM_UTC
# Number of seconds since the epoch.
.L "void tminit(Tm_zone_t* zone)" Implicitly called by the other tm library routines to initialize global data, including the .L tm_info.format table and the .L tm_info.flags global flags. Global data should only be modified after an explicit call to .LR tminit . If .L "zone != 0" then it specifies a time zone other that the local time zone.
.L "void tmset(Tm_zone_t* zone);" .L tmset sets the reference timezoe to .LR zone . .L tm_info.local points to the local timezone and .L tm_info.zone points to the current reference timezone.
.L "time_t tmleap(time_t* clock)" Returns a .L time_t value for the time pointed to by .L clock with leap seconds adjusted for external routines that do not handle leap seconds. If .L clock is .L NULL then the current time is used. Adjustments are only done if the .L TM_ADJUST flag is set in .LR tm_info.flags .
.L "struct tm* tmmake(time_t* clock)" Returns a pointer to the .L tm struct corresponding to the time pointed to by .LR clock . If .L clock is .L NULL then the current time is used.
.L "time_t tmtime(struct tm* tp, int west)" Returns the .L time_t value corresponding to .LR tp . If .L west is .L TM_LOCALZONE then .L tm is relative to the local time zone, otherwise .L west is the number of minutes west of UTC with daylight savings time taken into account. .LR tp->tm_wday , .LR tp->tm_yday and .L tp->tm_isdst are ignored in the conversion.
The library routines use a table of date strings pointed to by .LR "char** tm_info.format" . The indices in .L tm_info.format are fixed by category. .L tm_info.format may be changed to point to other tables according to local language and date conventions. The contents by index (showing the USA English values) are:
0 0-11 3-character abbreviated month names.
12-23 Full month names.
24-30 3-character abbreviated weekday names.
31-37 Full weekday names.
38 .L tmform() local time format used by the %X field.
39 .L tmform() local date format used by the %x field.
40 .L tmform() format used if the .L format argument is .L NULL or empty.
41-42 Meridian names: AM, PM.
43-46 UTC time zone names: GMT, UTC, UCT, CUT.
47-50 Daylight savings time suffix names: DST.
51-54 Suffixes to be ignored when matching strings in .LR tmform() .
55-61 Time part names: second, hour, minute, day, week, month, year.
62-65 Hours of the day names: midnight, morning, noon, evening.
66-68 Relative day names: yesterday, today, tomorrow.
69-71 Past relative time references: last, ago, past.
72-75 Current relative time references: this, now, current.
75-77 Future relative time references: next, hence, coming.
78-80 Exact relative time references: exactly.
81-85 Noise words to be ignored: at, in, on.
Low level support functions and data are described in .LR <tm.h> .