.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
+.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
.\"
.\" References consulted:
.\" Linux libc source code
.\" Modified 2001-12-13, joey, aeb
.\" Modified 2004-11-16, mtk
.\"
-.TH CTIME 3 2009-03-15 "" "Linux Programmer's Manual"
+.TH CTIME 3 2019-03-06 "" "Linux Programmer's Manual"
.SH NAME
asctime, ctime, gmtime, localtime, mktime, asctime_r, ctime_r, gmtime_r,
localtime_r \- transform date and time to broken-down time or ASCII
.SH SYNOPSIS
.nf
.B #include <time.h>
-.sp
+.PP
.BI "char *asctime(const struct tm *" tm );
-.br
.BI "char *asctime_r(const struct tm *" tm ", char *" buf );
-.sp
+.PP
.BI "char *ctime(const time_t *" timep );
-.br
.BI "char *ctime_r(const time_t *" timep ", char *" buf );
-.sp
+.PP
.BI "struct tm *gmtime(const time_t *" timep );
-.br
.BI "struct tm *gmtime_r(const time_t *" timep ", struct tm *" result );
-.sp
+.PP
.BI "struct tm *localtime(const time_t *" timep );
-.br
.BI "struct tm *localtime_r(const time_t *" timep ", struct tm *" result );
-.sp
+.PP
.BI "time_t mktime(struct tm *" tm );
.fi
-.sp
+.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
-.sp
+.ad l
+.PP
.BR asctime_r (),
.BR ctime_r (),
.BR gmtime_r (),
.BR localtime_r ():
-.br
-_POSIX_C_SOURCE\ >=\ 1 || _XOPEN_SOURCE || _BSD_SOURCE ||
-_SVID_SOURCE || _POSIX_SOURCE
+.RS
+_POSIX_C_SOURCE
+ || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
+.RE
+.ad
.SH DESCRIPTION
The
.BR ctime (),
and
.BR localtime ()
functions all take
-an argument of data type \fItime_t\fP which represents calendar time.
+an argument of data type \fItime_t\fP, which represents calendar time.
When interpreted as an absolute time value, it represents the number of
-seconds elapsed since 00:00:00 on January 1, 1970, Coordinated Universal
-Time (UTC).
+seconds elapsed since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).
.PP
The
.BR asctime ()
and
.BR mktime ()
functions both take an argument
-representing broken-down time which is a representation
-separated into year, month, day, etc.
+representing broken-down time, which is a representation
+separated into year, month, day, and so on.
.PP
Broken-down time is stored
-in the structure \fItm\fP which is defined in \fI<time.h>\fP as follows:
-.sp
+in the structure \fItm\fP, which is defined in \fI<time.h>\fP as follows:
+.PP
.in +4n
-.nf
+.EX
struct tm {
- int tm_sec; /* seconds */
- int tm_min; /* minutes */
- int tm_hour; /* hours */
- int tm_mday; /* day of the month */
- int tm_mon; /* month */
- int tm_year; /* year */
- int tm_wday; /* day of the week */
- int tm_yday; /* day in the year */
- int tm_isdst; /* daylight saving time */
+ int tm_sec; /* Seconds (0\-60) */
+ int tm_min; /* Minutes (0\-59) */
+ int tm_hour; /* Hours (0\-23) */
+ int tm_mday; /* Day of the month (1\-31) */
+ int tm_mon; /* Month (0\-11) */
+ int tm_year; /* Year \- 1900 */
+ int tm_wday; /* Day of the week (0\-6, Sunday = 0) */
+ int tm_yday; /* Day in the year (0\-365, 1 Jan = 0) */
+ int tm_isdst; /* Daylight saving time */
};
-.fi
+.EE
.in
.PP
The members of the \fItm\fP structure are:
.BI asctime(localtime( t )) \fR.
It converts the calendar time \fIt\fP into a
null-terminated string of the form
-.sp
-.RS
-"Wed Jun 30 21:49:08 1993\\n"
-.RE
-.sp
+.PP
+.in +4n
+.EX
+"Wed Jun 30 21:49:08 1993\en"
+.EE
+.in
+.PP
The abbreviations for the days of the week are "Sun", "Mon", "Tue", "Wed",
"Thu", "Fri", and "Sat".
The abbreviations for the months are "Jan",
The
.BR localtime ()
function converts the calendar time \fItimep\fP to
-broken-time representation, expressed relative to the user's specified
-timezone.
+broken-down time representation,
+expressed relative to the user's specified timezone.
The function acts as if it called
.BR tzset (3)
and sets the external variables \fItzname\fP with
.BR mktime ()
should (use timezone information and system databases to)
attempt to determine whether DST is in effect at the specified time.
-
+.PP
The
.BR mktime ()
function modifies the fields of the
.BR mktime ()
also sets the external variable \fItzname\fP with
information about the current timezone.
-
+.PP
If the specified broken-down
time cannot be represented as calendar time (seconds since the Epoch),
.BR mktime ()
-returns a value of
+returns
.I (time_t)\ \-1
and does not alter the
members of the broken-down time structure.
-.SH "RETURN VALUE"
-Each of these functions returns the value described, or NULL
-(\-1 in case of
-.BR mktime ())
-in case an error was detected.
-.SH "CONFORMING TO"
+.SH RETURN VALUE
+On success,
+.BR gmtime ()
+and
+.BR localtime ()
+return a pointer to a
+.IR "struct\ tm" .
+.PP
+On success,
+.BR gmtime_r ()
+and
+.BR localtime_r ()
+return the address of the structure pointed to by
+.IR result .
+.PP
+On success,
+.BR asctime ()
+and
+.BR ctime ()
+return a pointer to a string.
+.PP
+On success,
+.BR asctime_r ()
+and
+.BR ctime_r ()
+return a pointer to the string pointed to by
+.IR buf .
+.PP
+On success,
+.BR mktime ()
+returns the calendar time (seconds since the Epoch),
+expressed as a value of type
+.IR time_t .
+.PP
+On error,
+.BR mktime ()
+returns the value
+.IR "(time_t)\ -1" .
+The remaining functions return NULL on error.
+On error,
+.I errno
+is set to indicate the cause of the error.
+.SH ERRORS
+.TP
+.B EOVERFLOW
+The result cannot be represented.
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.ad l
+.TS
+allbox;
+lbw14 lb lbw31
+l l l.
+Interface Attribute Value
+T{
+.BR asctime ()
+T} Thread safety MT-Unsafe race:asctime locale
+T{
+.BR asctime_r ()
+T} Thread safety MT-Safe locale
+T{
+.BR ctime ()
+T} Thread safety T{
+MT-Unsafe race:tmbuf
+.br
+race:asctime env locale
+T}
+T{
+.BR ctime_r (),
+.BR gmtime_r (),
+.BR localtime_r (),
+.BR mktime ()
+T} Thread safety MT-Safe env locale
+T{
+.BR gmtime (),
+.BR localtime ()
+T} Thread safety MT-Unsafe race:tmbuf env locale
+.TE
+.ad
+.SH CONFORMING TO
POSIX.1-2001.
C89 and C99 specify
.BR asctime (),
and
.BR localtime ()
return a pointer to static data and hence are not thread-safe.
-Thread-safe versions
+The thread-safe versions,
.BR asctime_r (),
.BR ctime_r (),
.BR gmtime_r ()
and
-.BR localtime_r ()
-are specified by SUSv2, and available since libc 5.2.5.
-
+.BR localtime_r (),
+are specified by SUSv2.
+.PP
POSIX.1-2001 says:
"The
.BR asctime (),
Execution of any of the functions may overwrite the information returned
in either of these objects by any of the other functions."
This can occur in the glibc implementation.
-.LP
+.PP
In many implementations, including glibc, a 0 in
.I tm_mday
is interpreted as meaning the last day of the preceding month.
-.LP
+.PP
The glibc version of \fIstruct tm\fP has additional fields
-.sp
-.RS
-.nf
-long tm_gmtoff; /* Seconds east of UTC */
+.PP
+.in +4n
+.EX
const char *tm_zone; /* Timezone abbreviation */
-.fi
-.RE
-.sp
+.EE
+.in
+.PP
defined when
.B _BSD_SOURCE
was set before including
.IR <time.h> .
This is a BSD extension, present in 4.3BSD-Reno.
-
+.PP
According to POSIX.1-2004,
.BR localtime ()
is required to behave as though
-.BR tzset ()
+.BR tzset (3)
was called, while
.BR localtime_r ()
does not have this requirement.
.\" See http://thread.gmane.org/gmane.comp.time.tz/2034/
-For portable code
-.BR tzset ()
+For portable code,
+.BR tzset (3)
should be called before
.BR localtime_r ().
-.SH "SEE ALSO"
+.SH SEE ALSO
.BR date (1),
.BR gettimeofday (2),
.BR time (2),
projects / thirdparty / man-pages.git / blobdiff