man3type/tm.3type

   1 .\" Copyright (c) 2022 by Alejandro Colomar <colomar.6.4.3@gmail.com>
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .\"
   6 .TH TM 3type 2022-06-15 "Linux man-pages (unreleased)"
   7 .SH NAME
   8 tm \- broken-down time
   9 .SH LIBRARY
  10 Standard C library
  11 .RI ( libc )
  12 .SH SYNOPSIS
  13 .nf
  14 .B #include <time.h>
  15 .PP
  16 .B struct tm {
  17 .BR "    int         tm_sec;" "    /* Seconds          [" 0 ", " 60 "] */"
  18 .BR "    int         tm_min;" "    /* Minutes          [" 0 ", " 59 "] */"
  19 .BR "    int         tm_hour;" "   /* Hour             [" 0 ", " 23 "] */"
  20 .BR "    int         tm_mday;" "   /* Day of the month [" 1 ", " 31 "] */"
  21 .BR "    int         tm_mon;" \
  22 "    /* Month            [" 0 ", " 11 "]  (January = " 0 ") */"
  23 .BR "    int         tm_year;" "   /* Year minus " 1900 " */"
  24 .BR "    int         tm_wday;" \
  25 "   /* Day of the week  [" 0 ", " 6 "]   (Sunday = " 0 ") */"
  26 .BR "    int         tm_yday;" \
  27 "   /* Day of the year  [" 0 ", " 365 "] (Jan/01 = " 0 ") */"
  28 .BR "    int         tm_isdst;" "  /* Daylight savings flag */"
  29 .PP
  30 .BR "    long        tm_gmtoff;" " /* Seconds East of UTC */"
  31 .BR "    const char *tm_zone;" "   /* Timezone abbreviation */"
  32 .B };
  33 .fi
  34 .PP
  35 .RS -4
  36 Feature Test Macro Requirements for glibc (see
  37 .BR feature_test_macros (7)):
  38 .RE
  39 .PP
  40 .IR tm_gmtoff ,
  41 .IR tm_zone :
  42 .nf
  43 .\" Guarded with __USE_MISC:
  44     Since glibc 2.20:
  45         _DEFAULT_SOURCE
  46     Glibc 2.20 and earlier:
  47         _BSD_SOURCE
  48 .fi
  49 .SH DESCRIPTION
  50 Describes time, broken down into distinct components.
  51 .PP
  52 .I tm_isdst
  53 describes whether daylight saving time is in effect at the time described.
  54 The value is positive if daylight saving time is in effect,
  55 zero if it is not,
  56 and negative if the information is not available.
  57 .PP
  58 .I tm_gmtoff
  59 is the difference, in seconds,
  60 of the timezone represented by this broken-down time and UTC
  61 (this is the additive inverse of
  62 .BR timezone (3)).
  63 .PP
  64 .I tm_zone
  65 is the equivalent of
  66 .BR tzname (3)
  67 for the timezone represented by this broken-down time.
  68 .SH VERSIONS
  69 In C90,
  70 .I tm_sec
  71 could represent values in the range
  72 .RB [ 0 ", " 61 ],
  73 which could represent a double leap second.
  74 UTC doesn't permit double leap seconds,
  75 so it was limited to
  76 .B 60
  77 in C99.
  78 .SH STANDARDS
  79 C90 and later;
  80 POSIX.1-2001 and later.
  81 .PP
  82 .I tm_gmtoff
  83 and
  84 .I tm_zone
  85 originate from 4.3BSD-Tahoe (where
  86 .I tm_zone
  87 is a
  88 .IR "char *" ).
  89 .SH NOTES
  90 .I tm_sec
  91 can represent a leap second with the value
  92 .BR 60 .
  93 .PP
  94 .BR timezone (3),
  95 as a variable, is an XSI extension: some systems provide the V7-compatible
  96 .\" FreeBSD
  97 .BR timezone (3)
  98 function.
  99 The
 100 .I tm_gmtoff
 101 field provides an alternative (with the opposite sign) for those systems.
 102 .PP
 103 .I tm_zone
 104 points to static storage and may be overridden on subsequent calls to
 105 .BR localtime (3)
 106 and similar functions (however, this never happens under glibc).
 107 .SH SEE ALSO
 108 .BR ctime (3),
 109 .BR strftime (3),
 110 .BR strptime (3),
 111 .BR time (7)