TMDATE(2) TMDATE(2)
NAME
tmnow, tzload, tmtime, tmparse, tmfmt, tmnorm - convert date
and time
SYNOPSIS
#include <u.h>
#include <libc.h>
typedef struct Tm Tm;
typedef struct Tmfmt Tmfmt;
typedef struct Tzone Tzone;
struct Tm {
int nsec; /* nanoseconds (range 0..1e9) */
int sec; /* seconds (range 0..59) */
int min; /* minutes (0..59) */
int hour; /* hours (0..23) */
int mday; /* day of the month (1..31) */
int mon; /* month of the year (0..11) */
int year; /* C.E year - 1900 */
int wday; /* day of week (0..6, Sunday = 0) */
int yday; /* day of year (0..365) */
char zone[]; /* time zone name */
int tzoff; /* time zone delta from GMT, seconds */
Tzone *tz; /* the time zone (optional) */
};
Tzone *tzload(char *name);
Tm *tmnow(Tm *tm, Tzone *tz);
Tm *tmtime(Tm *tm, vlong abs, Tzone *tz);
Tm *tmtimens(Tm *tm, vlong abs, int ns, Tzone *tz);
Tm *tmparse(Tm *dst, char *fmt, char *tm, Tzone *zone, char **ep);
vlong tmnorm(Tm *tm);
Tmfmt tmfmt(Tm *tm, char *fmt);
void tmfmtinstall(void);
DESCRIPTION
This family of functions handles simple date and time manip-
ulation.
Time zones are loaded by name. They can be specified as the
abbreviated timezone name, the full timezone name, the path
to a timezone file, or an absolute offset in the HHMM form.
When given as a timezone, any instant-dependent adjustments
such as leap seconds and daylight savings time will be
applied to the derived fields of struct Tm, but will not
affect the absolute time. The time zone name local always
refers to the time in /env/timezone. The nil timezone
always refers to GMT.
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Tzload loads a timezone by name. The returned timezone is
cached for the lifetime of the program, and should not be
freed. Loading a timezone repeatedly by name loads from the
cache, and does not leak.
Tmnow gets the current time of day in the requested time
zone.
Tmtime converts the second resolution timestamp 'abs' into a
Tm struct in the requested timezone. Tmtimens does the
same, but with a nanosecond accuracy.
Tmtimens is identical to tmtime, but accepts a nanosecond
argument.
Tmparse parses a time from a string according to the format
argument. Leading whitespace is ignored. The point at
which the parsing stopped is returned in ep. If ep is nil,
trailing garbage is ignored. The result is returned in the
timezone requested. If there is a timezone in the date, and
a timezone is provided when parsing, then the zone is
shifted to the provided timezone. Parsing is case-
insensitive
The format argument contains zero or more of the following
components:
Y, YY, YYYY
Represents the year. YY prints the year in 2 digit
form.
M, MM, MMM, MMMM
The month of the year, in unpadded numeric, padded
numeric, short name, or long name, respectively.
D, DD
The day of month in unpadded or padded numeric form,
respectively.
W, WW, WWW
The day of week in numeric, short or long name form,
respectively.
h, hh
The hour in unpadded or padded form, respectively
m, mm
The minute in unpadded or padded form, respectively
s, ss
The second in unpadded or padded form, respectively
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TMDATE(2) TMDATE(2)
t, tt, ttt
The milliseconds in unpadded and padded form, respec-
tively.
u, uu, uuu, uuuu
The microseconds in unpadded. padded form modulo mil-
liseconds, or unpadded, padded forms of the complete
value, respectively.
n, nn, nnn, nnnn, nnnnn, nnnnnn
The nanoseconds in unpadded and padded form modulo mil-
liseconds, the unpadded and padded form modulo
microseconds, and the unpadded and padded complete
value, respectively.
Z, ZZ, ZZZ
The timezone in [+-]HHMM and [+-]HH:MM, and named form,
respectively. If the named timezone matches the name
of the local zone, then the local timezone will be
used. Otherwise, we will attempt to use the named
zones listed in RFC5322.
a, A Lower and uppercase 'am' and 'pm' specifiers, respec-
tively.
o Ordinal day of month suffix specifier.
[...]
Quoted text, copied directly to the output.
_ When formatting, this inserts padding into the date
format. The padded width of a field is the sum of for-
mat and specifier characters combined. When For exam-
ple, __h will format to a width of 3. When parsing,
this acts as whitespace.
? When parsing, all formats of the following argument are
tried from most to least specific. For example, ?M
will match January, Jan, 01, and 1, in that order. When
formatting, ? is ignored.
~ When parsing a date, this slackens range enforcement,
accepting out of range values such as January 32, which
would get normalized to February 1st.
Any characters not specified above are copied directly to
output, without modification.
Tmfmt produces a format description structure suitable for
passing to fmtprint(2). If fmt is nil, we default to the
format used in ctime(2). The format of the format string is
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TMDATE(2) TMDATE(2)
identical to tmparse.
When parsing, any amount of whitespace is treated as a sin-
gle token. All string matches are case insensitive, and
zero padding is optional.
Tmnorm takes a manually adjusted Tm structure, and normal-
izes it, returning the absolute timestamp that the date rep-
resents. Normalizing recomputes the year, mon, mday, hr,
min, sec and tzoff fields. If tz is non-nil, then tzoff
will be recomputed, taking into account daylight savings for
the absolute time. The values not used in the computation
are recomputed for the resulting absolute time. All out of
range values are wrapped. For example, December 32 will
roll over to Jan 1 of the following year.
Tmfmtinstall installs a time format specifier %τ. The time
format behaves as in tmfmt
EXAMPLES
All examples assume tmfmtinstall has been called.
Get the current date in the local timezone, UTC, and
US_Pacific time. Print it using the default format.
Tm t;
Tzone *zl, *zp;
if((zl = tzload("local") == nil)
sysfatal("load zone: %r");
if((zp = tzload("US_Pacific") == nil)
sysfatal("load zone: %r");
print("local: %τ\n", tmfmt(tmnow(&t, zl), nil));
print("gmt: %τ\n", tmfmt(tmnow(&t, nil), nil));
print("eastern: %τ\n", tmfmt(tmnow(&t, zp), nil));
Compare if two times are the same, regardless of timezone.
Done with full, strict error checking.
#define Fmt "?WWW, ?MM ?DD hh:mm:ss ?Z YYYY"
Tm a, b;
char *e, *est, *pst;
pst = "Tue Dec 10 12:36:00 PST 2019";
est = "Tue Dec 10 15:36:00 EST 2019";
if(tmparse(&a, Fmt, pst, nil, &e) == nil)
sysfatal("failed to parse: %r");
if(*e != '\0')
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sysfatal("trailing junk %s", e);
if(tmparse(&b, Fmt, est, nil, &e) == nil)
sysfatal("failed to parse: %r");
if(*e != '\0')
sysfatal("trailing junk %s", e);
if(tmnorm(a) == tmnorm(b) && a.nsec == b.nsec)
print("same\n");
else
print("different\n");
Convert from one timezone to another.
Tm here, there;
Tzone *zl, *zp;
if((zl = tzload("local")) == nil)
sysfatal("load zone: %r");
if((zp = tzload("US_Pacific")) == nil)
sysfatal("load zone: %r");
if(tmnow(&here, zl) == nil)
sysfatal("get time: %r");
if(tmtime(&there, tmnorm(&here), zp) == nil)
sysfatal("shift time: %r");
Add a day. Because cross daylight savings, only 23 hours are
added.
Tm t;
char *date = "Sun Nov 2 13:11:11 PST 2019";
if(tmparse(&t, "W MMM D hh:mm:ss z YYYY, date, nil) == nil)
print("failed to parse");
t.mday++;
tmnorm(&t);
print("%τ", tmfmt(&t, nil)); /* Mon Nov 3 13:11:11 PST 2019 */
BUGS
Checking the timezone name against the local timezone is a
dirty hack. The same date string may parse differently for
people in different timezones.
Tmparse and ctime don't mix. Tmparse preserves timezone
names, including names like '+0200'. Ctime expects timezone
names to be exactly three characters. Use the %τ format
character instead of ctime.
The timezone information that we ship is out of date.
The Plan 9 timezone format has no way to express leap
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seconds.
We provide no way to manipulate timezones.
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