1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
|
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
.TH "TIME" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" time
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
time \- get time
.SH SYNOPSIS
.LP
\fB#include <time.h>
.br
.sp
time_t time(time_t *\fP\fItloc\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
The \fItime\fP() function shall return the value of time \ in seconds
since the Epoch.
.LP
The \fItloc\fP argument points to an area where the return value is
also stored. If \fItloc\fP is a null pointer, no value is
stored.
.SH RETURN VALUE
.LP
Upon successful completion, \fItime\fP() shall return the value of
time. Otherwise, (\fBtime_t\fP)-1 shall be returned.
.SH ERRORS
.LP
No errors are defined.
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Getting the Current Time
.LP
The following example uses the \fItime\fP() function to calculate
the time elapsed, in seconds, since the Epoch, \fIlocaltime\fP() to
convert that value to a broken-down time, and \fIasctime\fP() to convert
the broken-down time values into a printable string.
.sp
.RS
.nf
\fB#include <stdio.h>
#include <time.h>
.sp
int main(void)
{
time_t result;
.sp
result = time(NULL);
printf("%s%ju secs since the Epoch\\n",
asctime(localtime(&result)),
(uintmax_t)result);
return(0);
}
\fP
.fi
.RE
.LP
This example writes the current time to \fIstdout\fP in a form like
this:
.sp
.RS
.nf
\fBWed Jun 26 10:32:15 1996
835810335 secs since the Epoch
\fP
.fi
.RE
.SS Timing an Event
.LP
The following example gets the current time, prints it out in the
user's format, and prints the number of minutes to an event
being timed.
.sp
.RS
.nf
\fB#include <time.h>
#include <stdio.h>
\&...
time_t now;
int minutes_to_event;
\&...
time(&now);
minutes_to_event = ...;
printf("The time is ");
puts(asctime(localtime(&now)));
printf("There are %d minutes to the event.\\n",
minutes_to_event);
\&...
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
The \fItime\fP() function returns a value in seconds (type \fBtime_t\fP)
while \fItimes\fP() returns a set of values in clock ticks (type \fBclock_t\fP).
Some historical
implementations, such as 4.3 BSD, have mechanisms capable of returning
more precise times (see below). A generalized timing scheme
to unify these various timing mechanisms has been proposed but not
adopted.
.LP
Implementations in which \fBtime_t\fP is a 32-bit signed integer (many
historical implementations) fail in the year 2038.
IEEE\ Std\ 1003.1-2001 does not address this problem. However, the
use of the \fBtime_t\fP type is mandated in order to
ease the eventual fix.
.LP
The use of the \fI<time.h>\fP header instead of \fI<sys/types.h>\fP
allows compatibility with the ISO\ C standard.
.LP
Many historical implementations (including Version 7) and the 1984
/usr/group standard use \fBlong\fP instead of \fBtime_t\fP.
This volume of IEEE\ Std\ 1003.1-2001 uses the latter type in order
to agree with the ISO\ C standard.
.LP
4.3 BSD includes \fItime\fP() only as an alternate function to the
more flexible \fIgettimeofday\fP() function.
.SH FUTURE DIRECTIONS
.LP
In a future version of this volume of IEEE\ Std\ 1003.1-2001, \fBtime_t\fP
is likely to be required to be capable of
representing times far in the future. Whether this will be mandated
as a 64-bit type or a requirement that a specific date in the
future be representable (for example, 10000 AD) is not yet determined.
Systems purchased after the approval of this volume of
IEEE\ Std\ 1003.1-2001 should be evaluated to determine whether their
lifetime will extend past 2038.
.SH SEE ALSO
.LP
\fIasctime\fP(), \fIclock\fP(), \fIctime\fP()
, \fIdifftime\fP(), \fIgettimeofday\fP(), \fIgmtime\fP(), \fIlocaltime\fP()
, \fImktime\fP() ,
\fIstrftime\fP(), \fIstrptime\fP(), \fIutime\fP(), the Base Definitions
volume of IEEE\ Std\ 1003.1-2001, \fI<time.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
|
