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ctime.3 (2918B)
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1 .TH CTIME 3
2 .SH NAME
3 asctime, ctime, gmtime, localtime, mktime - transform date and time to
4 broken-down time
5 .SH SYNOPSIS
6 #include <time.h>
7
8 .nf
9 char *asctime(const struct tm *tm);
10 char *ctime(const time_t *timep);
11 struct tm *gmtime(const time_t *timep);
12 struct tm *localtime(const time_t *timep);
13 time_t mktime(struct tm *tm);
14 .fi
15 .SH DESCRIPTION
16 The
17 .BR ctime ,
18 .B gmtime
19 and
20 .B localtime
21 functions all take an argument of data type
22 .BR time_t ,
23 which represents calendar time.
24
25 The
26 .B asctime
27 and
28 .B mktime
29 functions both takes an argument representing broken-down time,
30 which is a representation separated into year, month, day and so on.
31
32 Broken-down time is stored in the struct tm.
33
34 The call
35 .B ctime(t)
36 is equivalent to
37 .BR asctime(localtime(t)) .
38 It converts the calendar time
39 .I t
40 into a null-terminated string of the form:
41
42 "Wed Jun 30 21:49:08 1993\\n\\0"
43
44 In C locale, the abbreviations for the days of the week are
45 "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", and "Sat";
46 the abbreviations for the months are "Jan", "Feb", "Mar", "Apr",
47 "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", and "Dec".
48
49 The
50 .B gmtime
51 function converts the calendar time
52 .I timep
53 into broken-down time representation, expressed as
54 Coordinated Universal Time (UTC).
55 It may return NULL if the specified time cannot be converted to UTC.
56
57 The
58 .B localtime
59 function converts the calendar time
60 .I timep
61 to broken-down time representation,
62 expressed relative to the user's specified timezone.
63
64 The
65 .B asctime
66 function converts the broken-down time value
67 .I tm
68 into a null-terminated string with the same format as
69 .B ctime
70 function.
71
72 The
73 .B mktime
74 function converts a broken-down time structure,
75 expressed as local time, to calendar time representation.
76 The function ignores
77 the values supplied by the caller in the
78 .B tm_wday
79 and
80 .B tm_yday
81 fields and the original values of other fields
82 are not restricted to the ranges indicated above.
83 On successful completion, the values of
84 .B tm_wday
85 and
86 .B tm_yday
87 are set appropriately and the other components are set to represent
88 the specified calendar time within their respective ranges.
89 The final value of
90 .B tm_mday
91 is not set until
92 .B tm_mon
93 and
94 .B tm_year
95 are determined.
96
97 .SH RETURN VALUE
98 On success,
99 .B gmtime
100 and
101 .B localtime
102 functions return a pointer to a struct tm.
103
104 On success,
105 .B asctime
106 and
107 .B ctime
108 functions return a pointer to a string.
109
110 On success,
111 .B mktime
112 function returns the calendar time, expressed as a value of type
113 .BR time_t .
114
115 On error,
116 .B mktime
117 function returns the value
118 .BR (time_t)-1 .
119 The remaining functions return NULL on error.
120 On error,
121 .B errno
122 is set to indicate the cause of the error.
123 .SH STANDARDS
124 .nf
125 ISO/IEC 9899:1999 7.23.2.3 Paragraph 1,2,3
126 ISO/IEC 9899:1999 7.23.3.1 Paragraph 1,2,3
127 ISO/IEC 9899:1999 7.23.3.2 Paragraph 1,2,3
128 ISO/IEC 9899:1999 7.23.3.3 Paragraph 1,2,3
129 ISO/IEC 9899:1999 7.23.3.4 Paragraph 1,2,3
130 .fi
131 .SH SEE ALSO
132 .BR time.h (3)