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Annotation of 43BSDTahoe/man/man3/ctime.3, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1980 Regents of the University of California.
        !             2: .\" All rights reserved.  The Berkeley software License Agreement
        !             3: .\" specifies the terms and conditions for redistribution.
        !             4: .\"
        !             5: .\"    @(#)ctime.3     6.9 (Berkeley) 9/30/87
        !             6: .\"
        !             7: .TH CTIME 3  "September 30, 1987"
        !             8: .UC 4
        !             9: .SH NAME
        !            10: ctime, localtime, gmtime, asctime, timezone, tzset \-  convert date and time to ASCII
        !            11: .SH SYNOPSIS
        !            12: .nf
        !            13: .B void tzset()
        !            14: .PP
        !            15: .B char *ctime(clock)
        !            16: .B time_t *clock;
        !            17: .PP
        !            18: .B #include <time.h>
        !            19: .PP
        !            20: .B char *asctime(tm)
        !            21: .B struct tm *tm;
        !            22: .PP
        !            23: .B struct tm *localtime(clock)
        !            24: .B time_t *clock;
        !            25: .PP
        !            26: .B struct tm *gmtime(clock)
        !            27: .B time_t *clock;
        !            28: .PP
        !            29: .B char *timezone(zone, dst)
        !            30: .fi
        !            31: .fi
        !            32: .SH DESCRIPTION
        !            33: \fITzset\fP uses the value of the environment variable \fBTZ\fP to
        !            34: set up the time conversion information used by \fIlocaltime\fP.
        !            35: .PP
        !            36: If \fBTZ\fP does not appear in the environment, the \fBTZDEFAULT\fP
        !            37: file (as defined in \fItzfile.h\fP) is used by \fIlocaltime\fP.  If
        !            38: this file fails for any reason, the GMT offset as provided by the
        !            39: kernel is used.  In this case, DST is ignored, resulting in the time
        !            40: being incorrect by some amount if DST is currently in effect.  If
        !            41: this fails for any reason, GMT is used.
        !            42: .PP
        !            43: If \fBTZ\fP appears in the environment but its value is a null string,
        !            44: Greenwich Mean Time is used; if \fBTZ\fP appears and begins with a
        !            45: slash, it is used as the absolute pathname of the \fItzfile\fP(5)-format
        !            46: file from which to read the time conversion information; if \fBTZ\fP
        !            47: appears and begins with a character other than a slash, it's used as
        !            48: a pathname relative to the system time conversion information directory,
        !            49: defined as \fBTZDIR\fP in the include file \fItzfile.h\fP.  If this file
        !            50: fails for any reason, the GMT offset as provided by the kernel is
        !            51: used, as described above.  If this fails for any reason, GMT is used.
        !            52: .PP
        !            53: Programs that always wish to use local wall clock time should explicitly
        !            54: remove the environmental variable \fBTZ\fP with \fIunsetenv\fP(3).
        !            55: .PP
        !            56: \fICtime\fP converts a long integer, pointed to by \fIclock\fP,
        !            57: such as returned by \fItime\fP(3), into ASCII and returns a pointer
        !            58: to a 26-character string in the following form.  All the fields
        !            59: have constant width.
        !            60: .PP
        !            61:     Sun Sep 16 01:03:52 1973\\n\\0
        !            62: .PP
        !            63: .I Localtime
        !            64: and
        !            65: .I gmtime
        !            66: return pointers to structures containing
        !            67: the broken-down time.
        !            68: .I Localtime
        !            69: corrects for the time zone and possible daylight savings time;
        !            70: .I gmtime
        !            71: converts directly to GMT, which is the time UNIX uses.
        !            72: .I Asctime
        !            73: converts a broken-down time to ASCII and returns a pointer
        !            74: to a 26-character string.
        !            75: .PP
        !            76: The structure declaration from the include file is:
        !            77: .PP
        !            78: .RS
        !            79: .nf
        !            80: .nr .0 .8i+\w'int tm_isdst'u
        !            81: .ta .5i \n(.0u \n(.0u+\w'/* 0-000'u+1n
        !            82: struct tm {
        !            83:        int tm_sec;     /* 0-59 seconds */
        !            84:        int tm_min;     /* 0-59 minutes */
        !            85:        int tm_hour;    /* 0-23 hour */
        !            86:        int tm_mday;    /* 1-31 day of month */
        !            87:        int tm_mon;     /* 0-11 month */
        !            88:        int tm_year;    /* 0-   year \- 1900 */
        !            89:        int tm_wday;    /* 0-6  day of week (Sunday = 0) */
        !            90:        int tm_yday;    /* 0-365        day of year */
        !            91:        int tm_isdst;   /* flag:        daylight savings time in effect */
        !            92:        char **tm_zone; /* abbreviation of timezone name */
        !            93:        long tm_gmtoff; /* offset from GMT in seconds */
        !            94: };
        !            95: .fi
        !            96: .RE
        !            97: .PP
        !            98: \fITm_isdst\fP is non-zero if a time zone adjustment such as Daylight
        !            99: Savings time is in effect.
        !           100: .PP
        !           101: \fITm_gmtoff\fP is the offset (in seconds) of the time represented
        !           102: from GMT, with positive values indicating East of Greenwich.
        !           103: .PP
        !           104: \fITimezone\fP remains for compatibility reasons only; it's impossible to
        !           105: reliably map timezone's arguments (\fIzone\fP, a "minutes west of GMT" value
        !           106: and \fIdst\fP, a "daylight saving time in effect" flag) to a time zone
        !           107: abbreviation.
        !           108: .PP
        !           109: If the environmental string \fITZNAME\fP exists, \fItimezone\fP returns
        !           110: its value, unless it consists of two comma separated strings, in which
        !           111: case the second string is returned if \fIdst\fP is non-zero, else
        !           112: the first string.  If \fITZNAME\fP doesn't exist, \fIzone\fP is checked
        !           113: for equality with a built-in table of values, in which case \fItimezone\fP
        !           114: returns the time zone or daylight time zone abbreviation associated with
        !           115: that value.  If the requested \fIzone\fP does not appear in the table, the
        !           116: difference from GMT is returned; e.g. in Afghanistan,
        !           117: \fItimezone(-(60*4+30), 0)\fP is appropriate because it is 4:30 ahead of
        !           118: GMT, and the string \fBGMT+4:30\fP is returned.  Programs that in the
        !           119: past used the \fItimezone\fP function should return the zone name as
        !           120: set by \fIlocaltime\fP to assure correctness.
        !           121: .SH FILES
        !           122: .ta \w'/etc/zoneinfo/localtime\0\0'u
        !           123: /etc/zoneinfo  time zone information directory
        !           124: .br
        !           125: /etc/zoneinfo/localtime        local time zone file
        !           126: .SH SEE ALSO
        !           127: gettimeofday(2), getenv(3), time(3), tzfile(5), environ(7)
        !           128: .SH NOTE
        !           129: The return values point to static data whose content is overwritten by
        !           130: each call.  The \fBtm_zone\fP field of a returned \fBstruct tm\fP
        !           131: points to a static array of characters, which will also be overwritten
        !           132: at the next call (and by calls to \fItzset\fP).

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