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5ce8f203 | 1 | @node Date and Time, Resource Usage And Limitation, Arithmetic, Top |
7a68c94a | 2 | @c %MENU% Functions for getting the date and time and formatting them nicely |
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3 | @chapter Date and Time |
4 | ||
5 | This chapter describes functions for manipulating dates and times, | |
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6 | including functions for determining what time it is and conversion |
7 | between different time representations. | |
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8 | |
9 | @menu | |
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10 | * Time Basics:: Concepts and definitions. |
11 | * Elapsed Time:: Data types to represent elapsed times | |
12 | * Processor And CPU Time:: Time a program has spent executing. | |
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13 | * Calendar Time:: Manipulation of ``real'' dates and times. |
14 | * Setting an Alarm:: Sending a signal after a specified time. | |
15 | * Sleeping:: Waiting for a period of time. | |
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16 | @end menu |
17 | ||
5ce8f203 | 18 | |
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19 | @node Time Basics |
20 | @section Time Basics | |
21 | @cindex time | |
5ce8f203 | 22 | |
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23 | Discussing time in a technical manual can be difficult because the word |
24 | ``time'' in English refers to lots of different things. In this manual, | |
25 | we use a rigorous terminology to avoid confusion, and the only thing we | |
26 | use the simple word ``time'' for is to talk about the abstract concept. | |
27 | ||
28 | A @dfn{calendar time} is a point in the time continuum, for example | |
9269924c | 29 | November 4, 1990, at 18:02.5 UTC. Sometimes this is called ``absolute |
99a20616 UD |
30 | time''. |
31 | @cindex calendar time | |
32 | ||
33 | We don't speak of a ``date'', because that is inherent in a calendar | |
34 | time. | |
35 | @cindex date | |
36 | ||
37 | An @dfn{interval} is a contiguous part of the time continuum between two | |
38 | calendar times, for example the hour between 9:00 and 10:00 on July 4, | |
39 | 1980. | |
40 | @cindex interval | |
41 | ||
42 | An @dfn{elapsed time} is the length of an interval, for example, 35 | |
43 | minutes. People sometimes sloppily use the word ``interval'' to refer | |
44 | to the elapsed time of some interval. | |
45 | @cindex elapsed time | |
46 | @cindex time, elapsed | |
47 | ||
48 | An @dfn{amount of time} is a sum of elapsed times, which need not be of | |
49 | any specific intervals. For example, the amount of time it takes to | |
50 | read a book might be 9 hours, independently of when and in how many | |
51 | sittings it is read. | |
52 | ||
53 | A @dfn{period} is the elapsed time of an interval between two events, | |
54 | especially when they are part of a sequence of regularly repeating | |
55 | events. | |
56 | @cindex period of time | |
57 | ||
58 | @dfn{CPU time} is like calendar time, except that it is based on the | |
59 | subset of the time continuum when a particular process is actively | |
60 | using a CPU. CPU time is, therefore, relative to a process. | |
28f540f4 | 61 | @cindex CPU time |
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62 | |
63 | @dfn{Processor time} is an amount of time that a CPU is in use. In | |
64 | fact, it's a basic system resource, since there's a limit to how much | |
65 | can exist in any given interval (that limit is the elapsed time of the | |
66 | interval times the number of CPUs in the processor). People often call | |
67 | this CPU time, but we reserve the latter term in this manual for the | |
68 | definition above. | |
28f540f4 | 69 | @cindex processor time |
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70 | |
71 | @node Elapsed Time | |
72 | @section Elapsed Time | |
73 | @cindex elapsed time | |
74 | ||
75 | One way to represent an elapsed time is with a simple arithmetic data | |
76 | type, as with the following function to compute the elapsed time between | |
77 | two calendar times. This function is declared in @file{time.h}. | |
78 | ||
99a20616 | 79 | @deftypefun double difftime (time_t @var{time1}, time_t @var{time0}) |
d08a7e4c | 80 | @standards{ISO, time.h} |
23e5b8cb | 81 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
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82 | The @code{difftime} function returns the number of seconds of elapsed |
83 | time between calendar time @var{time1} and calendar time @var{time0}, as | |
84 | a value of type @code{double}. The difference ignores leap seconds | |
85 | unless leap second support is enabled. | |
86 | ||
a7a93d50 | 87 | In @theglibc{}, you can simply subtract @code{time_t} values. But on |
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88 | other systems, the @code{time_t} data type might use some other encoding |
89 | where subtraction doesn't work directly. | |
90 | @end deftypefun | |
91 | ||
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92 | @Theglibc{} provides two data types specifically for representing |
93 | an elapsed time. They are used by various @glibcadj{} functions, and | |
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94 | you can use them for your own purposes too. They're exactly the same |
95 | except that one has a resolution in microseconds, and the other, newer | |
96 | one, is in nanoseconds. | |
97 | ||
99a20616 | 98 | @deftp {Data Type} {struct timeval} |
d08a7e4c | 99 | @standards{BSD, sys/time.h} |
99a20616 UD |
100 | @cindex timeval |
101 | The @code{struct timeval} structure represents an elapsed time. It is | |
102 | declared in @file{sys/time.h} and has the following members: | |
103 | ||
104 | @table @code | |
87a629c5 | 105 | @item time_t tv_sec |
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106 | This represents the number of whole seconds of elapsed time. |
107 | ||
108 | @item long int tv_usec | |
109 | This is the rest of the elapsed time (a fraction of a second), | |
110 | represented as the number of microseconds. It is always less than one | |
111 | million. | |
112 | ||
113 | @end table | |
114 | @end deftp | |
115 | ||
99a20616 | 116 | @deftp {Data Type} {struct timespec} |
d08a7e4c | 117 | @standards{POSIX.1, sys/time.h} |
99a20616 UD |
118 | @cindex timespec |
119 | The @code{struct timespec} structure represents an elapsed time. It is | |
120 | declared in @file{time.h} and has the following members: | |
121 | ||
122 | @table @code | |
87a629c5 | 123 | @item time_t tv_sec |
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124 | This represents the number of whole seconds of elapsed time. |
125 | ||
126 | @item long int tv_nsec | |
127 | This is the rest of the elapsed time (a fraction of a second), | |
128 | represented as the number of nanoseconds. It is always less than one | |
129 | billion. | |
130 | ||
131 | @end table | |
132 | @end deftp | |
133 | ||
134 | It is often necessary to subtract two values of type @w{@code{struct | |
135 | timeval}} or @w{@code{struct timespec}}. Here is the best way to do | |
136 | this. It works even on some peculiar operating systems where the | |
137 | @code{tv_sec} member has an unsigned type. | |
138 | ||
139 | @smallexample | |
01ae168d | 140 | @include timeval_subtract.c.texi |
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141 | @end smallexample |
142 | ||
b642f101 | 143 | Common functions that use @code{struct timeval} are @code{gettimeofday} |
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144 | and @code{settimeofday}. |
145 | ||
146 | ||
1f77f049 | 147 | There are no @glibcadj{} functions specifically oriented toward |
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148 | dealing with elapsed times, but the calendar time, processor time, and |
149 | alarm and sleeping functions have a lot to do with them. | |
150 | ||
151 | ||
152 | @node Processor And CPU Time | |
153 | @section Processor And CPU Time | |
154 | ||
155 | If you're trying to optimize your program or measure its efficiency, | |
156 | it's very useful to know how much processor time it uses. For that, | |
157 | calendar time and elapsed times are useless because a process may spend | |
158 | time waiting for I/O or for other processes to use the CPU. However, | |
159 | you can get the information with the functions in this section. | |
160 | ||
161 | CPU time (@pxref{Time Basics}) is represented by the data type | |
162 | @code{clock_t}, which is a number of @dfn{clock ticks}. It gives the | |
163 | total amount of time a process has actively used a CPU since some | |
a7a93d50 | 164 | arbitrary event. On @gnusystems{}, that event is the creation of the |
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165 | process. While arbitrary in general, the event is always the same event |
166 | for any particular process, so you can always measure how much time on | |
11bf311e | 167 | the CPU a particular computation takes by examining the process' CPU |
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168 | time before and after the computation. |
169 | @cindex CPU time | |
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170 | @cindex clock ticks |
171 | @cindex ticks, clock | |
99a20616 | 172 | |
a7a93d50 | 173 | On @gnulinuxhurdsystems{}, @code{clock_t} is equivalent to @code{long int} and |
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174 | @code{CLOCKS_PER_SEC} is an integer value. But in other systems, both |
175 | @code{clock_t} and the macro @code{CLOCKS_PER_SEC} can be either integer | |
176 | or floating-point types. Casting CPU time values to @code{double}, as | |
177 | in the example above, makes sure that operations such as arithmetic and | |
178 | printing work properly and consistently no matter what the underlying | |
179 | representation is. | |
180 | ||
181 | Note that the clock can wrap around. On a 32bit system with | |
182 | @code{CLOCKS_PER_SEC} set to one million this function will return the | |
183 | same value approximately every 72 minutes. | |
184 | ||
185 | For additional functions to examine a process' use of processor time, | |
88197030 | 186 | and to control it, see @ref{Resource Usage And Limitation}. |
99a20616 | 187 | |
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188 | |
189 | @menu | |
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190 | * CPU Time:: The @code{clock} function. |
191 | * Processor Time:: The @code{times} function. | |
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192 | @end menu |
193 | ||
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194 | @node CPU Time |
195 | @subsection CPU Time Inquiry | |
28f540f4 | 196 | |
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197 | To get a process' CPU time, you can use the @code{clock} function. This |
198 | facility is declared in the header file @file{time.h}. | |
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199 | @pindex time.h |
200 | ||
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201 | In typical usage, you call the @code{clock} function at the beginning |
202 | and end of the interval you want to time, subtract the values, and then | |
203 | divide by @code{CLOCKS_PER_SEC} (the number of clock ticks per second) | |
204 | to get processor time, like this: | |
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205 | |
206 | @smallexample | |
207 | @group | |
208 | #include <time.h> | |
209 | ||
210 | clock_t start, end; | |
99a20616 | 211 | double cpu_time_used; |
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212 | |
213 | start = clock(); | |
214 | @dots{} /* @r{Do the work.} */ | |
215 | end = clock(); | |
99a20616 | 216 | cpu_time_used = ((double) (end - start)) / CLOCKS_PER_SEC; |
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217 | @end group |
218 | @end smallexample | |
219 | ||
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220 | Do not use a single CPU time as an amount of time; it doesn't work that |
221 | way. Either do a subtraction as shown above or query processor time | |
222 | directly. @xref{Processor Time}. | |
223 | ||
28f540f4 | 224 | Different computers and operating systems vary wildly in how they keep |
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225 | track of CPU time. It's common for the internal processor clock |
226 | to have a resolution somewhere between a hundredth and millionth of a | |
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227 | second. |
228 | ||
28f540f4 | 229 | @deftypevr Macro int CLOCKS_PER_SEC |
d08a7e4c | 230 | @standards{ISO, time.h} |
28f540f4 | 231 | The value of this macro is the number of clock ticks per second measured |
99a20616 | 232 | by the @code{clock} function. POSIX requires that this value be one |
ce33f7be | 233 | million independent of the actual resolution. |
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234 | @end deftypevr |
235 | ||
28f540f4 | 236 | @deftp {Data Type} clock_t |
d08a7e4c | 237 | @standards{ISO, time.h} |
28f540f4 | 238 | This is the type of the value returned by the @code{clock} function. |
99a20616 | 239 | Values of type @code{clock_t} are numbers of clock ticks. |
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240 | @end deftp |
241 | ||
28f540f4 | 242 | @deftypefun clock_t clock (void) |
d08a7e4c | 243 | @standards{ISO, time.h} |
23e5b8cb AO |
244 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
245 | @c On Hurd, this calls task_info twice and adds user and system time | |
246 | @c from both basic and thread time info structs. On generic posix, | |
247 | @c calls times and adds utime and stime. On bsd, calls getrusage and | |
248 | @c safely converts stime and utime to clock. On linux, calls | |
249 | @c clock_gettime. | |
99a20616 | 250 | This function returns the calling process' current CPU time. If the CPU |
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251 | time is not available or cannot be represented, @code{clock} returns the |
252 | value @code{(clock_t)(-1)}. | |
253 | @end deftypefun | |
254 | ||
255 | ||
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256 | @node Processor Time |
257 | @subsection Processor Time Inquiry | |
28f540f4 | 258 | |
99a20616 UD |
259 | The @code{times} function returns information about a process' |
260 | consumption of processor time in a @w{@code{struct tms}} object, in | |
261 | addition to the process' CPU time. @xref{Time Basics}. You should | |
28f540f4 | 262 | include the header file @file{sys/times.h} to use this facility. |
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263 | @cindex processor time |
264 | @cindex CPU time | |
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265 | @pindex sys/times.h |
266 | ||
28f540f4 | 267 | @deftp {Data Type} {struct tms} |
d08a7e4c | 268 | @standards{POSIX.1, sys/times.h} |
28f540f4 RM |
269 | The @code{tms} structure is used to return information about process |
270 | times. It contains at least the following members: | |
271 | ||
272 | @table @code | |
273 | @item clock_t tms_utime | |
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274 | This is the total processor time the calling process has used in |
275 | executing the instructions of its program. | |
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276 | |
277 | @item clock_t tms_stime | |
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278 | This is the processor time the system has used on behalf of the calling |
279 | process. | |
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280 | |
281 | @item clock_t tms_cutime | |
282 | This is the sum of the @code{tms_utime} values and the @code{tms_cutime} | |
283 | values of all terminated child processes of the calling process, whose | |
284 | status has been reported to the parent process by @code{wait} or | |
285 | @code{waitpid}; see @ref{Process Completion}. In other words, it | |
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286 | represents the total processor time used in executing the instructions |
287 | of all the terminated child processes of the calling process, excluding | |
288 | child processes which have not yet been reported by @code{wait} or | |
28f540f4 | 289 | @code{waitpid}. |
99a20616 | 290 | @cindex child process |
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291 | |
292 | @item clock_t tms_cstime | |
99a20616 | 293 | This is similar to @code{tms_cutime}, but represents the total processor |
9269924c | 294 | time the system has used on behalf of all the terminated child processes |
99a20616 | 295 | of the calling process. |
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296 | @end table |
297 | ||
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298 | All of the times are given in numbers of clock ticks. Unlike CPU time, |
299 | these are the actual amounts of time; not relative to any event. | |
300 | @xref{Creating a Process}. | |
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301 | @end deftp |
302 | ||
4cfd8026 | 303 | @deftypevr Macro int CLK_TCK |
d08a7e4c | 304 | @standards{POSIX.1, time.h} |
4cfd8026 AJ |
305 | This is an obsolete name for the number of clock ticks per second. Use |
306 | @code{sysconf (_SC_CLK_TCK)} instead. | |
307 | @end deftypevr | |
308 | ||
28f540f4 | 309 | @deftypefun clock_t times (struct tms *@var{buffer}) |
d08a7e4c | 310 | @standards{POSIX.1, sys/times.h} |
23e5b8cb AO |
311 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
312 | @c On HURD, this calls task_info twice, for basic and thread times info, | |
313 | @c adding user and system times into tms, and then gettimeofday, to | |
314 | @c compute the real time. On BSD, it calls getclktck, getrusage (twice) | |
315 | @c and time. On Linux, it's a syscall with special handling to account | |
316 | @c for clock_t counts that look like error values. | |
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317 | The @code{times} function stores the processor time information for |
318 | the calling process in @var{buffer}. | |
319 | ||
4cfd8026 AJ |
320 | The return value is the number of clock ticks since an arbitrary point |
321 | in the past, e.g. since system start-up. @code{times} returns | |
322 | @code{(clock_t)(-1)} to indicate failure. | |
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323 | @end deftypefun |
324 | ||
325 | @strong{Portability Note:} The @code{clock} function described in | |
99a20616 | 326 | @ref{CPU Time} is specified by the @w{ISO C} standard. The |
a7a93d50 | 327 | @code{times} function is a feature of POSIX.1. On @gnusystems{}, the |
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328 | CPU time is defined to be equivalent to the sum of the @code{tms_utime} |
329 | and @code{tms_stime} fields returned by @code{times}. | |
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330 | |
331 | @node Calendar Time | |
332 | @section Calendar Time | |
333 | ||
99a20616 UD |
334 | This section describes facilities for keeping track of calendar time. |
335 | @xref{Time Basics}. | |
28f540f4 | 336 | |
1f77f049 | 337 | @Theglibc{} represents calendar time three ways: |
28f540f4 RM |
338 | |
339 | @itemize @bullet | |
01cdeca0 | 340 | @item |
3566d33c | 341 | @dfn{Simple time} (the @code{time_t} data type) is a compact |
99a20616 UD |
342 | representation, typically giving the number of seconds of elapsed time |
343 | since some implementation-specific base time. | |
3566d33c | 344 | @cindex simple time |
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345 | |
346 | @item | |
99a20616 UD |
347 | There is also a "high-resolution time" representation. Like simple |
348 | time, this represents a calendar time as an elapsed time since a base | |
349 | time, but instead of measuring in whole seconds, it uses a @code{struct | |
350 | timeval} data type, which includes fractions of a second. Use this time | |
351 | representation instead of simple time when you need greater precision. | |
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352 | @cindex high-resolution time |
353 | ||
354 | @item | |
3566d33c | 355 | @dfn{Local time} or @dfn{broken-down time} (the @code{struct tm} data |
99a20616 | 356 | type) represents a calendar time as a set of components specifying the |
3566d33c | 357 | year, month, and so on in the Gregorian calendar, for a specific time |
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358 | zone. This calendar time representation is usually used only to |
359 | communicate with people. | |
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360 | @cindex local time |
361 | @cindex broken-down time | |
3566d33c UD |
362 | @cindex Gregorian calendar |
363 | @cindex calendar, Gregorian | |
28f540f4 RM |
364 | @end itemize |
365 | ||
366 | @menu | |
367 | * Simple Calendar Time:: Facilities for manipulating calendar time. | |
368 | * High-Resolution Calendar:: A time representation with greater precision. | |
369 | * Broken-down Time:: Facilities for manipulating local time. | |
3566d33c | 370 | * High Accuracy Clock:: Maintaining a high accuracy system clock. |
99a20616 | 371 | * Formatting Calendar Time:: Converting times to strings. |
e9dcb080 UD |
372 | * Parsing Date and Time:: Convert textual time and date information back |
373 | into broken-down time values. | |
28f540f4 | 374 | * TZ Variable:: How users specify the time zone. |
01cdeca0 | 375 | * Time Zone Functions:: Functions to examine or specify the time zone. |
28f540f4 RM |
376 | * Time Functions Example:: An example program showing use of some of |
377 | the time functions. | |
378 | @end menu | |
379 | ||
380 | @node Simple Calendar Time | |
381 | @subsection Simple Calendar Time | |
382 | ||
3566d33c UD |
383 | This section describes the @code{time_t} data type for representing calendar |
384 | time as simple time, and the functions which operate on simple time objects. | |
28f540f4 RM |
385 | These facilities are declared in the header file @file{time.h}. |
386 | @pindex time.h | |
387 | ||
388 | @cindex epoch | |
28f540f4 | 389 | @deftp {Data Type} time_t |
d08a7e4c | 390 | @standards{ISO, time.h} |
3566d33c | 391 | This is the data type used to represent simple time. Sometimes, it also |
99a20616 UD |
392 | represents an elapsed time. When interpreted as a calendar time value, |
393 | it represents the number of seconds elapsed since 00:00:00 on January 1, | |
394 | 1970, Coordinated Universal Time. (This calendar time is sometimes | |
395 | referred to as the @dfn{epoch}.) POSIX requires that this count not | |
396 | include leap seconds, but on some systems this count includes leap seconds | |
60092701 | 397 | if you set @code{TZ} to certain values (@pxref{TZ Variable}). |
28f540f4 | 398 | |
99a20616 UD |
399 | Note that a simple time has no concept of local time zone. Calendar |
400 | Time @var{T} is the same instant in time regardless of where on the | |
401 | globe the computer is. | |
3566d33c | 402 | |
1f77f049 | 403 | In @theglibc{}, @code{time_t} is equivalent to @code{long int}. |
28f540f4 RM |
404 | In other systems, @code{time_t} might be either an integer or |
405 | floating-point type. | |
406 | @end deftp | |
407 | ||
99a20616 UD |
408 | The function @code{difftime} tells you the elapsed time between two |
409 | simple calendar times, which is not always as easy to compute as just | |
410 | subtracting. @xref{Elapsed Time}. | |
28f540f4 | 411 | |
28f540f4 | 412 | @deftypefun time_t time (time_t *@var{result}) |
d08a7e4c | 413 | @standards{ISO, time.h} |
23e5b8cb | 414 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
99a20616 UD |
415 | The @code{time} function returns the current calendar time as a value of |
416 | type @code{time_t}. If the argument @var{result} is not a null pointer, | |
417 | the calendar time value is also stored in @code{*@var{result}}. If the | |
418 | current calendar time is not available, the value | |
419 | @w{@code{(time_t)(-1)}} is returned. | |
28f540f4 RM |
420 | @end deftypefun |
421 | ||
3566d33c UD |
422 | @c The GNU C library implements stime() with a call to settimeofday() on |
423 | @c Linux. | |
8ded91fb | 424 | @deftypefun int stime (const time_t *@var{newtime}) |
d08a7e4c RJ |
425 | @standards{SVID, time.h} |
426 | @standards{XPG, time.h} | |
23e5b8cb AO |
427 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
428 | @c On unix, this is implemented in terms of settimeofday. | |
11bf311e | 429 | @code{stime} sets the system clock, i.e., it tells the system that the |
99a20616 | 430 | current calendar time is @var{newtime}, where @code{newtime} is |
3566d33c UD |
431 | interpreted as described in the above definition of @code{time_t}. |
432 | ||
433 | @code{settimeofday} is a newer function which sets the system clock to | |
434 | better than one second precision. @code{settimeofday} is generally a | |
435 | better choice than @code{stime}. @xref{High-Resolution Calendar}. | |
436 | ||
437 | Only the superuser can set the system clock. | |
438 | ||
439 | If the function succeeds, the return value is zero. Otherwise, it is | |
440 | @code{-1} and @code{errno} is set accordingly: | |
441 | ||
442 | @table @code | |
443 | @item EPERM | |
444 | The process is not superuser. | |
445 | @end table | |
446 | @end deftypefun | |
447 | ||
448 | ||
28f540f4 RM |
449 | |
450 | @node High-Resolution Calendar | |
451 | @subsection High-Resolution Calendar | |
452 | ||
3566d33c | 453 | The @code{time_t} data type used to represent simple times has a |
28f540f4 RM |
454 | resolution of only one second. Some applications need more precision. |
455 | ||
1f77f049 | 456 | So, @theglibc{} also contains functions which are capable of |
28f540f4 RM |
457 | representing calendar times to a higher resolution than one second. The |
458 | functions and the associated data types described in this section are | |
459 | declared in @file{sys/time.h}. | |
460 | @pindex sys/time.h | |
461 | ||
28f540f4 | 462 | @deftp {Data Type} {struct timezone} |
d08a7e4c | 463 | @standards{BSD, sys/time.h} |
28f540f4 RM |
464 | The @code{struct timezone} structure is used to hold minimal information |
465 | about the local time zone. It has the following members: | |
466 | ||
467 | @table @code | |
468 | @item int tz_minuteswest | |
f0f1bf85 | 469 | This is the number of minutes west of UTC. |
28f540f4 RM |
470 | |
471 | @item int tz_dsttime | |
76c23bac | 472 | If nonzero, Daylight Saving Time applies during some part of the year. |
28f540f4 RM |
473 | @end table |
474 | ||
475 | The @code{struct timezone} type is obsolete and should never be used. | |
476 | Instead, use the facilities described in @ref{Time Zone Functions}. | |
477 | @end deftp | |
478 | ||
28f540f4 | 479 | @deftypefun int gettimeofday (struct timeval *@var{tp}, struct timezone *@var{tzp}) |
d08a7e4c | 480 | @standards{BSD, sys/time.h} |
23e5b8cb AO |
481 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
482 | @c On most GNU/Linux systems this is a direct syscall, but the posix/ | |
483 | @c implementation (not used on GNU/Linux or GNU/Hurd) relies on time and | |
484 | @c localtime_r, saving and restoring tzname in an unsafe manner. | |
485 | @c On some GNU/Linux variants, ifunc resolvers are used in shared libc | |
486 | @c for vdso resolution. ifunc-vdso-revisit. | |
99a20616 UD |
487 | The @code{gettimeofday} function returns the current calendar time as |
488 | the elapsed time since the epoch in the @code{struct timeval} structure | |
489 | indicated by @var{tp}. (@pxref{Elapsed Time} for a description of | |
0cb71e02 | 490 | @code{struct timeval}). Information about the time zone is returned in |
9269924c | 491 | the structure pointed to by @var{tzp}. If the @var{tzp} argument is a null |
99a20616 | 492 | pointer, time zone information is ignored. |
28f540f4 RM |
493 | |
494 | The return value is @code{0} on success and @code{-1} on failure. The | |
495 | following @code{errno} error condition is defined for this function: | |
496 | ||
497 | @table @code | |
498 | @item ENOSYS | |
499 | The operating system does not support getting time zone information, and | |
a7a93d50 | 500 | @var{tzp} is not a null pointer. @gnusystems{} do not |
28f540f4 RM |
501 | support using @w{@code{struct timezone}} to represent time zone |
502 | information; that is an obsolete feature of 4.3 BSD. | |
503 | Instead, use the facilities described in @ref{Time Zone Functions}. | |
504 | @end table | |
505 | @end deftypefun | |
506 | ||
28f540f4 | 507 | @deftypefun int settimeofday (const struct timeval *@var{tp}, const struct timezone *@var{tzp}) |
d08a7e4c | 508 | @standards{BSD, sys/time.h} |
23e5b8cb AO |
509 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
510 | @c On HURD, it calls host_set_time with a privileged port. On other | |
511 | @c unix systems, it's a syscall. | |
99a20616 UD |
512 | The @code{settimeofday} function sets the current calendar time in the |
513 | system clock according to the arguments. As for @code{gettimeofday}, | |
514 | the calendar time is represented as the elapsed time since the epoch. | |
515 | As for @code{gettimeofday}, time zone information is ignored if | |
516 | @var{tzp} is a null pointer. | |
28f540f4 RM |
517 | |
518 | You must be a privileged user in order to use @code{settimeofday}. | |
519 | ||
3566d33c UD |
520 | Some kernels automatically set the system clock from some source such as |
521 | a hardware clock when they start up. Others, including Linux, place the | |
99a20616 | 522 | system clock in an ``invalid'' state (in which attempts to read the clock |
3566d33c UD |
523 | fail). A call of @code{stime} removes the system clock from an invalid |
524 | state, and system startup scripts typically run a program that calls | |
525 | @code{stime}. | |
526 | ||
527 | @code{settimeofday} causes a sudden jump forwards or backwards, which | |
528 | can cause a variety of problems in a system. Use @code{adjtime} (below) | |
529 | to make a smooth transition from one time to another by temporarily | |
530 | speeding up or slowing down the clock. | |
531 | ||
532 | With a Linux kernel, @code{adjtimex} does the same thing and can also | |
533 | make permanent changes to the speed of the system clock so it doesn't | |
534 | need to be corrected as often. | |
535 | ||
28f540f4 RM |
536 | The return value is @code{0} on success and @code{-1} on failure. The |
537 | following @code{errno} error conditions are defined for this function: | |
538 | ||
539 | @table @code | |
540 | @item EPERM | |
99a20616 | 541 | This process cannot set the clock because it is not privileged. |
28f540f4 RM |
542 | |
543 | @item ENOSYS | |
544 | The operating system does not support setting time zone information, and | |
545 | @var{tzp} is not a null pointer. | |
546 | @end table | |
547 | @end deftypefun | |
548 | ||
3566d33c | 549 | @c On Linux, GNU libc implements adjtime() as a call to adjtimex(). |
28f540f4 | 550 | @deftypefun int adjtime (const struct timeval *@var{delta}, struct timeval *@var{olddelta}) |
d08a7e4c | 551 | @standards{BSD, sys/time.h} |
23e5b8cb AO |
552 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
553 | @c On hurd and mach, call host_adjust_time with a privileged port. On | |
554 | @c Linux, it's implemented in terms of adjtimex. On other unixen, it's | |
555 | @c a syscall. | |
28f540f4 | 556 | This function speeds up or slows down the system clock in order to make |
99a20616 UD |
557 | a gradual adjustment. This ensures that the calendar time reported by |
558 | the system clock is always monotonically increasing, which might not | |
559 | happen if you simply set the clock. | |
28f540f4 RM |
560 | |
561 | The @var{delta} argument specifies a relative adjustment to be made to | |
99a20616 UD |
562 | the clock time. If negative, the system clock is slowed down for a |
563 | while until it has lost this much elapsed time. If positive, the system | |
564 | clock is speeded up for a while. | |
28f540f4 RM |
565 | |
566 | If the @var{olddelta} argument is not a null pointer, the @code{adjtime} | |
567 | function returns information about any previous time adjustment that | |
568 | has not yet completed. | |
569 | ||
570 | This function is typically used to synchronize the clocks of computers | |
571 | in a local network. You must be a privileged user to use it. | |
3566d33c UD |
572 | |
573 | With a Linux kernel, you can use the @code{adjtimex} function to | |
574 | permanently change the clock speed. | |
575 | ||
28f540f4 RM |
576 | The return value is @code{0} on success and @code{-1} on failure. The |
577 | following @code{errno} error condition is defined for this function: | |
578 | ||
579 | @table @code | |
580 | @item EPERM | |
581 | You do not have privilege to set the time. | |
582 | @end table | |
583 | @end deftypefun | |
584 | ||
585 | @strong{Portability Note:} The @code{gettimeofday}, @code{settimeofday}, | |
01cdeca0 | 586 | and @code{adjtime} functions are derived from BSD. |
28f540f4 RM |
587 | |
588 | ||
3566d33c UD |
589 | Symbols for the following function are declared in @file{sys/timex.h}. |
590 | ||
3566d33c | 591 | @deftypefun int adjtimex (struct timex *@var{timex}) |
d08a7e4c | 592 | @standards{GNU, sys/timex.h} |
23e5b8cb AO |
593 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
594 | @c It's a syscall, only available on linux. | |
3566d33c UD |
595 | |
596 | @code{adjtimex} is functionally identical to @code{ntp_adjtime}. | |
597 | @xref{High Accuracy Clock}. | |
598 | ||
599 | This function is present only with a Linux kernel. | |
600 | ||
601 | @end deftypefun | |
602 | ||
28f540f4 RM |
603 | @node Broken-down Time |
604 | @subsection Broken-down Time | |
605 | @cindex broken-down time | |
606 | @cindex calendar time and broken-down time | |
607 | ||
1f77f049 | 608 | Calendar time is represented by the usual @glibcadj{} functions as an |
99a20616 UD |
609 | elapsed time since a fixed base calendar time. This is convenient for |
610 | computation, but has no relation to the way people normally think of | |
611 | calendar time. By contrast, @dfn{broken-down time} is a binary | |
612 | representation of calendar time separated into year, month, day, and so | |
613 | on. Broken-down time values are not useful for calculations, but they | |
614 | are useful for printing human readable time information. | |
28f540f4 | 615 | |
3566d33c | 616 | A broken-down time value is always relative to a choice of time |
99a20616 | 617 | zone, and it also indicates which time zone that is. |
28f540f4 RM |
618 | |
619 | The symbols in this section are declared in the header file @file{time.h}. | |
620 | ||
28f540f4 | 621 | @deftp {Data Type} {struct tm} |
d08a7e4c | 622 | @standards{ISO, time.h} |
28f540f4 | 623 | This is the data type used to represent a broken-down time. The structure |
99a20616 | 624 | contains at least the following members, which can appear in any order. |
28f540f4 RM |
625 | |
626 | @table @code | |
627 | @item int tm_sec | |
99a20616 UD |
628 | This is the number of full seconds since the top of the minute (normally |
629 | in the range @code{0} through @code{59}, but the actual upper limit is | |
630 | @code{60}, to allow for leap seconds if leap second support is | |
631 | available). | |
28f540f4 RM |
632 | @cindex leap second |
633 | ||
634 | @item int tm_min | |
99a20616 UD |
635 | This is the number of full minutes since the top of the hour (in the |
636 | range @code{0} through @code{59}). | |
28f540f4 RM |
637 | |
638 | @item int tm_hour | |
99a20616 UD |
639 | This is the number of full hours past midnight (in the range @code{0} through |
640 | @code{23}). | |
28f540f4 RM |
641 | |
642 | @item int tm_mday | |
99a20616 UD |
643 | This is the ordinal day of the month (in the range @code{1} through @code{31}). |
644 | Watch out for this one! As the only ordinal number in the structure, it is | |
645 | inconsistent with the rest of the structure. | |
28f540f4 RM |
646 | |
647 | @item int tm_mon | |
99a20616 UD |
648 | This is the number of full calendar months since the beginning of the |
649 | year (in the range @code{0} through @code{11}). Watch out for this one! | |
650 | People usually use ordinal numbers for month-of-year (where January = 1). | |
28f540f4 RM |
651 | |
652 | @item int tm_year | |
99a20616 | 653 | This is the number of full calendar years since 1900. |
28f540f4 RM |
654 | |
655 | @item int tm_wday | |
99a20616 UD |
656 | This is the number of full days since Sunday (in the range @code{0} through |
657 | @code{6}). | |
28f540f4 RM |
658 | |
659 | @item int tm_yday | |
99a20616 UD |
660 | This is the number of full days since the beginning of the year (in the |
661 | range @code{0} through @code{365}). | |
28f540f4 RM |
662 | |
663 | @item int tm_isdst | |
664 | @cindex Daylight Saving Time | |
665 | @cindex summer time | |
666 | This is a flag that indicates whether Daylight Saving Time is (or was, or | |
667 | will be) in effect at the time described. The value is positive if | |
668 | Daylight Saving Time is in effect, zero if it is not, and negative if the | |
669 | information is not available. | |
670 | ||
671 | @item long int tm_gmtoff | |
672 | This field describes the time zone that was used to compute this | |
f0f1bf85 UD |
673 | broken-down time value, including any adjustment for daylight saving; it |
674 | is the number of seconds that you must add to UTC to get local time. | |
675 | You can also think of this as the number of seconds east of UTC. For | |
676 | example, for U.S. Eastern Standard Time, the value is @code{-5*60*60}. | |
677 | The @code{tm_gmtoff} field is derived from BSD and is a GNU library | |
f65fd747 | 678 | extension; it is not visible in a strict @w{ISO C} environment. |
28f540f4 RM |
679 | |
680 | @item const char *tm_zone | |
f0f1bf85 UD |
681 | This field is the name for the time zone that was used to compute this |
682 | broken-down time value. Like @code{tm_gmtoff}, this field is a BSD and | |
f65fd747 | 683 | GNU extension, and is not visible in a strict @w{ISO C} environment. |
28f540f4 RM |
684 | @end table |
685 | @end deftp | |
686 | ||
99a20616 | 687 | |
28f540f4 | 688 | @deftypefun {struct tm *} localtime (const time_t *@var{time}) |
d08a7e4c | 689 | @standards{ISO, time.h} |
23e5b8cb AO |
690 | @safety{@prelim{}@mtunsafe{@mtasurace{:tmbuf} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
691 | @c Calls tz_convert with a static buffer. | |
692 | @c localtime @mtasurace:tmbuf @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
693 | @c tz_convert dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
3566d33c | 694 | The @code{localtime} function converts the simple time pointed to by |
28f540f4 RM |
695 | @var{time} to broken-down time representation, expressed relative to the |
696 | user's specified time zone. | |
697 | ||
698 | The return value is a pointer to a static broken-down time structure, which | |
60092701 RM |
699 | might be overwritten by subsequent calls to @code{ctime}, @code{gmtime}, |
700 | or @code{localtime}. (But no other library function overwrites the contents | |
701 | of this object.) | |
28f540f4 | 702 | |
fe0ec73e UD |
703 | The return value is the null pointer if @var{time} cannot be represented |
704 | as a broken-down time; typically this is because the year cannot fit into | |
705 | an @code{int}. | |
706 | ||
fbf964ae PE |
707 | Calling @code{localtime} also sets the current time zone as if |
708 | @code{tzset} were called. @xref{Time Zone Functions}. | |
28f540f4 RM |
709 | @end deftypefun |
710 | ||
0413b54c UD |
711 | Using the @code{localtime} function is a big problem in multi-threaded |
712 | programs. The result is returned in a static buffer and this is used in | |
76c23bac | 713 | all threads. POSIX.1c introduced a variant of this function. |
0413b54c | 714 | |
0413b54c | 715 | @deftypefun {struct tm *} localtime_r (const time_t *@var{time}, struct tm *@var{resultp}) |
d08a7e4c | 716 | @standards{POSIX.1c, time.h} |
23e5b8cb AO |
717 | @safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
718 | @c localtime_r @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
719 | @c tz_convert(use_localtime) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
720 | @c libc_lock_lock dup @asulock @aculock | |
721 | @c tzset_internal @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
722 | @c always called with tzset_lock held | |
723 | @c sets static is_initialized before initialization; | |
724 | @c reads and sets old_tz; sets tz_rules. | |
725 | @c some of the issues only apply on the first call. | |
726 | @c subsequent calls only trigger these when called by localtime; | |
727 | @c otherwise, they're ok. | |
728 | @c getenv dup @mtsenv | |
729 | @c strcmp dup ok | |
730 | @c strdup @ascuheap | |
731 | @c tzfile_read @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
732 | @c memcmp dup ok | |
733 | @c strstr dup ok | |
734 | @c getenv dup @mtsenv | |
735 | @c asprintf dup @mtslocale @ascuheap @acsmem | |
736 | @c stat64 dup ok | |
737 | @c fopen dup @ascuheap @asulock @acsmem @acsfd @aculock | |
738 | @c fileno dup ok | |
739 | @c fstat64 dup ok | |
740 | @c fclose dup @ascuheap @asulock @aculock @acsmem @acsfd | |
741 | @c free dup @ascuheap @acsmem | |
742 | @c fsetlocking dup ok [no @mtasurace:stream @asulock, exclusive] | |
743 | @c fread_unlocked dup ok [no @mtasurace:stream @asucorrupt @acucorrupt] | |
744 | @c memcpy dup ok | |
745 | @c decode ok | |
746 | @c bswap_32 dup ok | |
747 | @c fseek dup ok [no @mtasurace:stream @asucorrupt @acucorrupt] | |
748 | @c ftello dup ok [no @mtasurace:stream @asucorrupt @acucorrupt] | |
749 | @c malloc dup @ascuheap @acsmem | |
750 | @c decode64 ok | |
751 | @c bswap_64 dup ok | |
752 | @c getc_unlocked ok [no @mtasurace:stream @asucorrupt @acucorrupt] | |
753 | @c tzstring dup @ascuheap @acsmem | |
754 | @c compute_tzname_max dup ok [guarded by tzset_lock] | |
755 | @c memset dup ok | |
756 | @c update_vars ok [guarded by tzset_lock] | |
757 | @c sets daylight, timezone, tzname and tzname_cur_max; | |
758 | @c called only with tzset_lock held, unless tzset_parse_tz | |
759 | @c (internal, but not static) gets called by users; given the its | |
760 | @c double-underscore-prefixed name, this interface violation could | |
761 | @c be regarded as undefined behavior. | |
762 | @c strlen ok | |
763 | @c tzset_parse_tz @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
764 | @c sscanf dup @mtslocale @ascuheap @acsmem | |
765 | @c isalnum dup @mtsenv | |
766 | @c tzstring @ascuheap @acsmem | |
767 | @c reads and changes tzstring_list without synchronization, but | |
768 | @c only called with tzset_lock held (save for interface violations) | |
769 | @c strlen dup ok | |
770 | @c malloc dup @ascuheap @acsmem | |
771 | @c strcpy dup ok | |
772 | @c isdigit dup @mtslocale | |
773 | @c compute_offset ok | |
774 | @c tzfile_default @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
775 | @c sets tzname, timezone, types, zone_names, rule_*off, etc; no guards | |
776 | @c strlen dup ok | |
777 | @c tzfile_read dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
778 | @c mempcpy dup ok | |
779 | @c compute_tzname_max ok [if guarded by tzset_lock] | |
780 | @c iterates over zone_names; no guards | |
781 | @c free dup @ascuheap @acsmem | |
782 | @c strtoul dup @mtslocale | |
783 | @c update_vars dup ok | |
784 | @c tzfile_compute(use_localtime) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
785 | @c sets tzname; no guards. with !use_localtime, as in gmtime, it's ok | |
786 | @c tzstring dup @acsuheap @acsmem | |
787 | @c tzset_parse_tz dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
788 | @c offtime dup ok | |
789 | @c tz_compute dup ok | |
790 | @c strcmp dup ok | |
791 | @c offtime ok | |
792 | @c isleap dup ok | |
793 | @c tz_compute ok | |
794 | @c compute_change ok | |
795 | @c isleap ok | |
796 | @c libc_lock_unlock dup @aculock | |
797 | ||
0413b54c | 798 | The @code{localtime_r} function works just like the @code{localtime} |
3566d33c | 799 | function. It takes a pointer to a variable containing a simple time |
0413b54c UD |
800 | and converts it to the broken-down time format. |
801 | ||
802 | But the result is not placed in a static buffer. Instead it is placed | |
803 | in the object of type @code{struct tm} to which the parameter | |
804 | @var{resultp} points. | |
805 | ||
806 | If the conversion is successful the function returns a pointer to the | |
807 | object the result was written into, i.e., it returns @var{resultp}. | |
808 | @end deftypefun | |
809 | ||
810 | ||
28f540f4 | 811 | @deftypefun {struct tm *} gmtime (const time_t *@var{time}) |
d08a7e4c | 812 | @standards{ISO, time.h} |
23e5b8cb AO |
813 | @safety{@prelim{}@mtunsafe{@mtasurace{:tmbuf} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
814 | @c gmtime @mtasurace:tmbuf @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
815 | @c tz_convert dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
28f540f4 | 816 | This function is similar to @code{localtime}, except that the broken-down |
3566d33c UD |
817 | time is expressed as Coordinated Universal Time (UTC) (formerly called |
818 | Greenwich Mean Time (GMT)) rather than relative to a local time zone. | |
28f540f4 | 819 | |
28f540f4 RM |
820 | @end deftypefun |
821 | ||
0413b54c | 822 | As for the @code{localtime} function we have the problem that the result |
f2ea0f5b | 823 | is placed in a static variable. POSIX.1c also provides a replacement for |
0413b54c UD |
824 | @code{gmtime}. |
825 | ||
0413b54c | 826 | @deftypefun {struct tm *} gmtime_r (const time_t *@var{time}, struct tm *@var{resultp}) |
d08a7e4c | 827 | @standards{POSIX.1c, time.h} |
23e5b8cb AO |
828 | @safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
829 | @c You'd think tz_convert could avoid some safety issues with | |
830 | @c !use_localtime, but no such luck: tzset_internal will always bring | |
831 | @c about all possible AS and AC problems when it's first called. | |
832 | @c Calling any of localtime,gmtime_r once would run the initialization | |
833 | @c and avoid the heap, mem and fd issues in gmtime* in subsequent calls, | |
834 | @c but the unsafe locking would remain. | |
835 | @c gmtime_r @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
836 | @c tz_convert(gmtime_r) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
0413b54c UD |
837 | This function is similar to @code{localtime_r}, except that it converts |
838 | just like @code{gmtime} the given time as Coordinated Universal Time. | |
839 | ||
840 | If the conversion is successful the function returns a pointer to the | |
841 | object the result was written into, i.e., it returns @var{resultp}. | |
842 | @end deftypefun | |
843 | ||
844 | ||
28f540f4 | 845 | @deftypefun time_t mktime (struct tm *@var{brokentime}) |
d08a7e4c | 846 | @standards{ISO, time.h} |
23e5b8cb AO |
847 | @safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
848 | @c mktime @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
849 | @c passes a static localtime_offset to mktime_internal; it is read | |
850 | @c once, used as an initial guess, and updated at the end, but not | |
851 | @c used except as a guess for subsequent calls, so it should be safe. | |
852 | @c Even though a compiler might delay the load and perform it multiple | |
853 | @c times (bug 16346), there are at least two unconditional uses of the | |
854 | @c auto variable in which the first load is stored, separated by a | |
855 | @c call to an external function, and a conditional change of the | |
856 | @c variable before the external call, so refraining from allocating a | |
857 | @c local variable at the first load would be a very bad optimization. | |
858 | @c tzset dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
859 | @c mktime_internal(localtime_r) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
860 | @c ydhms_diff ok | |
861 | @c ranged_convert(localtime_r) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
862 | @c *convert = localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
863 | @c time_t_avg dup ok | |
864 | @c guess_time_tm dup ok | |
865 | @c ydhms_diff dup ok | |
866 | @c time_t_add_ok ok | |
867 | @c time_t_avg ok | |
868 | @c isdst_differ ok | |
869 | @c time_t_int_add_ok ok | |
fbf964ae PE |
870 | The @code{mktime} function converts a broken-down time structure to a |
871 | simple time representation. It also normalizes the contents of the | |
872 | broken-down time structure, and fills in some components based on the | |
873 | values of the others. | |
28f540f4 RM |
874 | |
875 | The @code{mktime} function ignores the specified contents of the | |
fbf964ae PE |
876 | @code{tm_wday}, @code{tm_yday}, @code{tm_gmtoff}, and @code{tm_zone} |
877 | members of the broken-down time | |
3566d33c | 878 | structure. It uses the values of the other components to determine the |
28f540f4 | 879 | calendar time; it's permissible for these components to have |
76c23bac | 880 | unnormalized values outside their normal ranges. The last thing that |
28f540f4 | 881 | @code{mktime} does is adjust the components of the @var{brokentime} |
9dcc8f11 | 882 | structure, including the members that were initially ignored. |
28f540f4 | 883 | |
3566d33c | 884 | If the specified broken-down time cannot be represented as a simple time, |
28f540f4 RM |
885 | @code{mktime} returns a value of @code{(time_t)(-1)} and does not modify |
886 | the contents of @var{brokentime}. | |
887 | ||
fbf964ae PE |
888 | Calling @code{mktime} also sets the current time zone as if |
889 | @code{tzset} were called; @code{mktime} uses this information instead | |
890 | of @var{brokentime}'s initial @code{tm_gmtoff} and @code{tm_zone} | |
891 | members. @xref{Time Zone Functions}. | |
28f540f4 RM |
892 | @end deftypefun |
893 | ||
3566d33c | 894 | @deftypefun time_t timelocal (struct tm *@var{brokentime}) |
d08a7e4c | 895 | @standards{???, time.h} |
23e5b8cb AO |
896 | @safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
897 | @c Alias to mktime. | |
3566d33c UD |
898 | |
899 | @code{timelocal} is functionally identical to @code{mktime}, but more | |
900 | mnemonically named. Note that it is the inverse of the @code{localtime} | |
901 | function. | |
902 | ||
903 | @strong{Portability note:} @code{mktime} is essentially universally | |
904 | available. @code{timelocal} is rather rare. | |
905 | ||
906 | @end deftypefun | |
907 | ||
3566d33c | 908 | @deftypefun time_t timegm (struct tm *@var{brokentime}) |
d08a7e4c | 909 | @standards{???, time.h} |
23e5b8cb AO |
910 | @safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
911 | @c timegm @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
912 | @c gmtime_offset triggers the same caveats as localtime_offset in mktime. | |
913 | @c although gmtime_r, as called by mktime, might save some issues, | |
914 | @c tzset calls tzset_internal with always, which forces | |
915 | @c reinitialization, so all issues may arise. | |
916 | @c tzset dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
917 | @c mktime_internal(gmtime_r) @asulock @aculock | |
597636d7 | 918 | @c ..gmtime_r @asulock @aculock |
23e5b8cb AO |
919 | @c ... dup ok |
920 | @c tz_convert(!use_localtime) @asulock @aculock | |
921 | @c ... dup @asulock @aculock | |
922 | @c tzfile_compute(!use_localtime) ok | |
3566d33c UD |
923 | |
924 | @code{timegm} is functionally identical to @code{mktime} except it | |
925 | always takes the input values to be Coordinated Universal Time (UTC) | |
926 | regardless of any local time zone setting. | |
927 | ||
928 | Note that @code{timegm} is the inverse of @code{gmtime}. | |
929 | ||
930 | @strong{Portability note:} @code{mktime} is essentially universally | |
931 | available. @code{timegm} is rather rare. For the most portable | |
932 | conversion from a UTC broken-down time to a simple time, set | |
933 | the @code{TZ} environment variable to UTC, call @code{mktime}, then set | |
934 | @code{TZ} back. | |
935 | ||
936 | @end deftypefun | |
937 | ||
938 | ||
939 | ||
940 | @node High Accuracy Clock | |
941 | @subsection High Accuracy Clock | |
942 | ||
943 | @cindex time, high precision | |
944 | @cindex clock, high accuracy | |
945 | @pindex sys/timex.h | |
946 | @c On Linux, GNU libc implements ntp_gettime() and npt_adjtime() as calls | |
947 | @c to adjtimex(). | |
948 | The @code{ntp_gettime} and @code{ntp_adjtime} functions provide an | |
949 | interface to monitor and manipulate the system clock to maintain high | |
950 | accuracy time. For example, you can fine tune the speed of the clock | |
951 | or synchronize it with another time source. | |
952 | ||
953 | A typical use of these functions is by a server implementing the Network | |
954 | Time Protocol to synchronize the clocks of multiple systems and high | |
955 | precision clocks. | |
956 | ||
957 | These functions are declared in @file{sys/timex.h}. | |
958 | ||
959 | @tindex struct ntptimeval | |
960 | @deftp {Data Type} {struct ntptimeval} | |
99a20616 UD |
961 | This structure is used for information about the system clock. It |
962 | contains the following members: | |
3566d33c UD |
963 | @table @code |
964 | @item struct timeval time | |
99a20616 UD |
965 | This is the current calendar time, expressed as the elapsed time since |
966 | the epoch. The @code{struct timeval} data type is described in | |
967 | @ref{Elapsed Time}. | |
3566d33c UD |
968 | |
969 | @item long int maxerror | |
970 | This is the maximum error, measured in microseconds. Unless updated | |
971 | via @code{ntp_adjtime} periodically, this value will reach some | |
972 | platform-specific maximum value. | |
973 | ||
974 | @item long int esterror | |
975 | This is the estimated error, measured in microseconds. This value can | |
976 | be set by @code{ntp_adjtime} to indicate the estimated offset of the | |
99a20616 | 977 | system clock from the true calendar time. |
3566d33c UD |
978 | @end table |
979 | @end deftp | |
980 | ||
3566d33c | 981 | @deftypefun int ntp_gettime (struct ntptimeval *@var{tptr}) |
d08a7e4c | 982 | @standards{GNU, sys/timex.h} |
23e5b8cb AO |
983 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
984 | @c Wrapper for adjtimex. | |
3566d33c UD |
985 | The @code{ntp_gettime} function sets the structure pointed to by |
986 | @var{tptr} to current values. The elements of the structure afterwards | |
987 | contain the values the timer implementation in the kernel assumes. They | |
9269924c | 988 | might or might not be correct. If they are not, an @code{ntp_adjtime} |
3566d33c UD |
989 | call is necessary. |
990 | ||
991 | The return value is @code{0} on success and other values on failure. The | |
992 | following @code{errno} error conditions are defined for this function: | |
993 | ||
2fe82ca6 | 994 | @vtable @code |
3566d33c UD |
995 | @item TIME_ERROR |
996 | The precision clock model is not properly set up at the moment, thus the | |
997 | clock must be considered unsynchronized, and the values should be | |
998 | treated with care. | |
2fe82ca6 | 999 | @end vtable |
3566d33c UD |
1000 | @end deftypefun |
1001 | ||
1002 | @tindex struct timex | |
1003 | @deftp {Data Type} {struct timex} | |
1004 | This structure is used to control and monitor the system clock. It | |
1005 | contains the following members: | |
1006 | @table @code | |
1007 | @item unsigned int modes | |
1008 | This variable controls whether and which values are set. Several | |
1009 | symbolic constants have to be combined with @emph{binary or} to specify | |
1010 | the effective mode. These constants start with @code{MOD_}. | |
1011 | ||
1012 | @item long int offset | |
99a20616 UD |
1013 | This value indicates the current offset of the system clock from the true |
1014 | calendar time. The value is given in microseconds. If bit | |
1015 | @code{MOD_OFFSET} is set in @code{modes}, the offset (and possibly other | |
1016 | dependent values) can be set. The offset's absolute value must not | |
1017 | exceed @code{MAXPHASE}. | |
3566d33c UD |
1018 | |
1019 | ||
1020 | @item long int frequency | |
99a20616 UD |
1021 | This value indicates the difference in frequency between the true |
1022 | calendar time and the system clock. The value is expressed as scaled | |
1023 | PPM (parts per million, 0.0001%). The scaling is @code{1 << | |
1024 | SHIFT_USEC}. The value can be set with bit @code{MOD_FREQUENCY}, but | |
1025 | the absolute value must not exceed @code{MAXFREQ}. | |
3566d33c UD |
1026 | |
1027 | @item long int maxerror | |
1028 | This is the maximum error, measured in microseconds. A new value can be | |
1029 | set using bit @code{MOD_MAXERROR}. Unless updated via | |
1030 | @code{ntp_adjtime} periodically, this value will increase steadily | |
1031 | and reach some platform-specific maximum value. | |
1032 | ||
1033 | @item long int esterror | |
1034 | This is the estimated error, measured in microseconds. This value can | |
1035 | be set using bit @code{MOD_ESTERROR}. | |
1036 | ||
1037 | @item int status | |
1038 | This variable reflects the various states of the clock machinery. There | |
1039 | are symbolic constants for the significant bits, starting with | |
1040 | @code{STA_}. Some of these flags can be updated using the | |
1041 | @code{MOD_STATUS} bit. | |
1042 | ||
1043 | @item long int constant | |
1044 | This value represents the bandwidth or stiffness of the PLL (phase | |
1045 | locked loop) implemented in the kernel. The value can be changed using | |
1046 | bit @code{MOD_TIMECONST}. | |
1047 | ||
1048 | @item long int precision | |
1049 | This value represents the accuracy or the maximum error when reading the | |
1050 | system clock. The value is expressed in microseconds. | |
1051 | ||
1052 | @item long int tolerance | |
1053 | This value represents the maximum frequency error of the system clock in | |
1054 | scaled PPM. This value is used to increase the @code{maxerror} every | |
1055 | second. | |
1056 | ||
1057 | @item struct timeval time | |
99a20616 | 1058 | The current calendar time. |
3566d33c UD |
1059 | |
1060 | @item long int tick | |
99a20616 | 1061 | The elapsed time between clock ticks in microseconds. A clock tick is a |
3566d33c UD |
1062 | periodic timer interrupt on which the system clock is based. |
1063 | ||
1064 | @item long int ppsfreq | |
1065 | This is the first of a few optional variables that are present only if | |
1066 | the system clock can use a PPS (pulse per second) signal to discipline | |
99a20616 UD |
1067 | the system clock. The value is expressed in scaled PPM and it denotes |
1068 | the difference in frequency between the system clock and the PPS signal. | |
3566d33c UD |
1069 | |
1070 | @item long int jitter | |
1071 | This value expresses a median filtered average of the PPS signal's | |
1072 | dispersion in microseconds. | |
1073 | ||
1074 | @item int shift | |
1075 | This value is a binary exponent for the duration of the PPS calibration | |
1076 | interval, ranging from @code{PPS_SHIFT} to @code{PPS_SHIFTMAX}. | |
1077 | ||
1078 | @item long int stabil | |
1079 | This value represents the median filtered dispersion of the PPS | |
1080 | frequency in scaled PPM. | |
1081 | ||
1082 | @item long int jitcnt | |
1083 | This counter represents the number of pulses where the jitter exceeded | |
1084 | the allowed maximum @code{MAXTIME}. | |
1085 | ||
1086 | @item long int calcnt | |
1087 | This counter reflects the number of successful calibration intervals. | |
1088 | ||
1089 | @item long int errcnt | |
1090 | This counter represents the number of calibration errors (caused by | |
1091 | large offsets or jitter). | |
1092 | ||
1093 | @item long int stbcnt | |
bbf70ae9 | 1094 | This counter denotes the number of calibrations where the stability |
3566d33c UD |
1095 | exceeded the threshold. |
1096 | @end table | |
1097 | @end deftp | |
1098 | ||
3566d33c | 1099 | @deftypefun int ntp_adjtime (struct timex *@var{tptr}) |
d08a7e4c | 1100 | @standards{GNU, sys/timex.h} |
23e5b8cb AO |
1101 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
1102 | @c Alias to adjtimex syscall. | |
3566d33c UD |
1103 | The @code{ntp_adjtime} function sets the structure specified by |
1104 | @var{tptr} to current values. | |
1105 | ||
1106 | In addition, @code{ntp_adjtime} updates some settings to match what you | |
1107 | pass to it in *@var{tptr}. Use the @code{modes} element of *@var{tptr} | |
1108 | to select what settings to update. You can set @code{offset}, | |
1109 | @code{freq}, @code{maxerror}, @code{esterror}, @code{status}, | |
1110 | @code{constant}, and @code{tick}. | |
1111 | ||
1112 | @code{modes} = zero means set nothing. | |
1113 | ||
1114 | Only the superuser can update settings. | |
1115 | ||
1116 | @c On Linux, ntp_adjtime() also does the adjtime() function if you set | |
1117 | @c modes = ADJ_OFFSET_SINGLESHOT (in fact, that is how GNU libc implements | |
1118 | @c adjtime()). But this should be considered an internal function because | |
1119 | @c it's so inconsistent with the rest of what ntp_adjtime() does and is | |
1120 | @c forced in an ugly way into the struct timex. So we don't document it | |
1121 | @c and instead document adjtime() as the way to achieve the function. | |
1122 | ||
1123 | The return value is @code{0} on success and other values on failure. The | |
1124 | following @code{errno} error conditions are defined for this function: | |
1125 | ||
1126 | @table @code | |
1127 | @item TIME_ERROR | |
1128 | The high accuracy clock model is not properly set up at the moment, thus the | |
1129 | clock must be considered unsynchronized, and the values should be | |
1130 | treated with care. Another reason could be that the specified new values | |
1131 | are not allowed. | |
1132 | ||
1133 | @item EPERM | |
1134 | The process specified a settings update, but is not superuser. | |
1135 | ||
1136 | @end table | |
1137 | ||
1138 | For more details see RFC1305 (Network Time Protocol, Version 3) and | |
1139 | related documents. | |
1140 | ||
1f77f049 | 1141 | @strong{Portability note:} Early versions of @theglibc{} did not |
3566d33c UD |
1142 | have this function but did have the synonymous @code{adjtimex}. |
1143 | ||
1144 | @end deftypefun | |
1145 | ||
1146 | ||
99a20616 UD |
1147 | @node Formatting Calendar Time |
1148 | @subsection Formatting Calendar Time | |
28f540f4 | 1149 | |
99a20616 UD |
1150 | The functions described in this section format calendar time values as |
1151 | strings. These functions are declared in the header file @file{time.h}. | |
28f540f4 RM |
1152 | @pindex time.h |
1153 | ||
28f540f4 | 1154 | @deftypefun {char *} asctime (const struct tm *@var{brokentime}) |
d08a7e4c | 1155 | @standards{ISO, time.h} |
23e5b8cb AO |
1156 | @safety{@prelim{}@mtunsafe{@mtasurace{:asctime} @mtslocale{}}@asunsafe{}@acsafe{}} |
1157 | @c asctime @mtasurace:asctime @mtslocale | |
1158 | @c Uses a static buffer. | |
1159 | @c asctime_internal @mtslocale | |
1160 | @c snprintf dup @mtslocale [no @acsuheap @acsmem] | |
1161 | @c ab_day_name @mtslocale | |
1162 | @c ab_month_name @mtslocale | |
28f540f4 RM |
1163 | The @code{asctime} function converts the broken-down time value that |
1164 | @var{brokentime} points to into a string in a standard format: | |
1165 | ||
1166 | @smallexample | |
1167 | "Tue May 21 13:46:22 1991\n" | |
1168 | @end smallexample | |
1169 | ||
1170 | The abbreviations for the days of week are: @samp{Sun}, @samp{Mon}, | |
1171 | @samp{Tue}, @samp{Wed}, @samp{Thu}, @samp{Fri}, and @samp{Sat}. | |
1172 | ||
1173 | The abbreviations for the months are: @samp{Jan}, @samp{Feb}, | |
1174 | @samp{Mar}, @samp{Apr}, @samp{May}, @samp{Jun}, @samp{Jul}, @samp{Aug}, | |
1175 | @samp{Sep}, @samp{Oct}, @samp{Nov}, and @samp{Dec}. | |
1176 | ||
1177 | The return value points to a statically allocated string, which might be | |
60092701 | 1178 | overwritten by subsequent calls to @code{asctime} or @code{ctime}. |
28f540f4 RM |
1179 | (But no other library function overwrites the contents of this |
1180 | string.) | |
1181 | @end deftypefun | |
1182 | ||
0413b54c | 1183 | @deftypefun {char *} asctime_r (const struct tm *@var{brokentime}, char *@var{buffer}) |
d08a7e4c | 1184 | @standards{POSIX.1c, time.h} |
23e5b8cb AO |
1185 | @safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}} |
1186 | @c asctime_r @mtslocale | |
1187 | @c asctime_internal dup @mtslocale | |
0413b54c UD |
1188 | This function is similar to @code{asctime} but instead of placing the |
1189 | result in a static buffer it writes the string in the buffer pointed to | |
76c23bac UD |
1190 | by the parameter @var{buffer}. This buffer should have room |
1191 | for at least 26 bytes, including the terminating null. | |
0413b54c UD |
1192 | |
1193 | If no error occurred the function returns a pointer to the string the | |
1194 | result was written into, i.e., it returns @var{buffer}. Otherwise | |
9269924c | 1195 | it returns @code{NULL}. |
0413b54c UD |
1196 | @end deftypefun |
1197 | ||
1198 | ||
28f540f4 | 1199 | @deftypefun {char *} ctime (const time_t *@var{time}) |
d08a7e4c | 1200 | @standards{ISO, time.h} |
23e5b8cb AO |
1201 | @safety{@prelim{}@mtunsafe{@mtasurace{:tmbuf} @mtasurace{:asctime} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
1202 | @c ctime @mtasurace:tmbuf @mtasurace:asctime @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1203 | @c localtime dup @mtasurace:tmbuf @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1204 | @c asctime dup @mtasurace:asctime @mtslocale | |
99a20616 UD |
1205 | The @code{ctime} function is similar to @code{asctime}, except that you |
1206 | specify the calendar time argument as a @code{time_t} simple time value | |
1207 | rather than in broken-down local time format. It is equivalent to | |
28f540f4 RM |
1208 | |
1209 | @smallexample | |
1210 | asctime (localtime (@var{time})) | |
1211 | @end smallexample | |
1212 | ||
fbf964ae PE |
1213 | Calling @code{ctime} also sets the current time zone as if |
1214 | @code{tzset} were called. @xref{Time Zone Functions}. | |
28f540f4 RM |
1215 | @end deftypefun |
1216 | ||
0413b54c | 1217 | @deftypefun {char *} ctime_r (const time_t *@var{time}, char *@var{buffer}) |
d08a7e4c | 1218 | @standards{POSIX.1c, time.h} |
23e5b8cb AO |
1219 | @safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
1220 | @c ctime_r @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1221 | @c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1222 | @c asctime_r dup @mtslocale | |
99a20616 UD |
1223 | This function is similar to @code{ctime}, but places the result in the |
1224 | string pointed to by @var{buffer}. It is equivalent to (written using | |
1225 | gcc extensions, @pxref{Statement Exprs,,,gcc,Porting and Using gcc}): | |
0413b54c UD |
1226 | |
1227 | @smallexample | |
1228 | (@{ struct tm tm; asctime_r (localtime_r (time, &tm), buf); @}) | |
1229 | @end smallexample | |
1230 | ||
1231 | If no error occurred the function returns a pointer to the string the | |
1232 | result was written into, i.e., it returns @var{buffer}. Otherwise | |
9269924c | 1233 | it returns @code{NULL}. |
0413b54c UD |
1234 | @end deftypefun |
1235 | ||
1236 | ||
28f540f4 | 1237 | @deftypefun size_t strftime (char *@var{s}, size_t @var{size}, const char *@var{template}, const struct tm *@var{brokentime}) |
d08a7e4c | 1238 | @standards{ISO, time.h} |
23e5b8cb AO |
1239 | @safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}} |
1240 | @c strftime @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd | |
1241 | @c strftime_l @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd | |
1242 | @c strftime_internal @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd | |
1243 | @c add ok | |
1244 | @c memset_zero dup ok | |
1245 | @c memset_space dup ok | |
1246 | @c strlen dup ok | |
1247 | @c mbrlen @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd [no @mtasurace:mbstate/!ps] | |
1248 | @c mbsinit dup ok | |
1249 | @c cpy ok | |
1250 | @c add dup ok | |
1251 | @c memcpy_lowcase ok | |
1252 | @c TOLOWER ok | |
1253 | @c tolower_l ok | |
1254 | @c memcpy_uppcase ok | |
1255 | @c TOUPPER ok | |
1256 | @c toupper_l ok | |
1257 | @c MEMCPY ok | |
1258 | @c memcpy dup ok | |
1259 | @c ISDIGIT ok | |
1260 | @c STRLEN ok | |
1261 | @c strlen dup ok | |
1262 | @c strftime_internal dup @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd | |
1263 | @c TOUPPER dup ok | |
1264 | @c nl_get_era_entry @ascuheap @asulock @acsmem @aculock | |
1265 | @c nl_init_era_entries @ascuheap @asulock @acsmem @aculock | |
1266 | @c libc_rwlock_wrlock dup @asulock @aculock | |
1267 | @c malloc dup @ascuheap @acsmem | |
1268 | @c memset dup ok | |
1269 | @c free dup @ascuheap @acsmem | |
1270 | @c realloc dup @ascuheap @acsmem | |
1271 | @c memcpy dup ok | |
1272 | @c strchr dup ok | |
1273 | @c wcschr dup ok | |
1274 | @c libc_rwlock_unlock dup @asulock @aculock | |
1275 | @c ERA_DATE_CMP ok | |
1276 | @c DO_NUMBER ok | |
1277 | @c DO_NUMBER_SPACEPAD ok | |
1278 | @c nl_get_alt_digit @ascuheap @asulock @acsmem @aculock | |
1279 | @c libc_rwlock_wrlock dup @asulock @aculock | |
1280 | @c nl_init_alt_digit @ascuheap @acsmem | |
1281 | @c malloc dup @ascuheap @acsmem | |
1282 | @c memset dup ok | |
1283 | @c strchr dup ok | |
1284 | @c libc_rwlock_unlock dup @aculock | |
1285 | @c memset_space ok | |
1286 | @c memset dup ok | |
1287 | @c memset_zero ok | |
1288 | @c memset dup ok | |
1289 | @c mktime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1290 | @c iso_week_days ok | |
1291 | @c isleap ok | |
1292 | @c tzset dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1293 | @c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1294 | @c gmtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1295 | @c tm_diff ok | |
28f540f4 RM |
1296 | This function is similar to the @code{sprintf} function (@pxref{Formatted |
1297 | Input}), but the conversion specifications that can appear in the format | |
1298 | template @var{template} are specialized for printing components of the date | |
1299 | and time @var{brokentime} according to the locale currently specified for | |
fbf964ae PE |
1300 | time conversion (@pxref{Locales}) and the current time zone |
1301 | (@pxref{Time Zone Functions}). | |
28f540f4 RM |
1302 | |
1303 | Ordinary characters appearing in the @var{template} are copied to the | |
1304 | output string @var{s}; this can include multibyte character sequences. | |
ec4b0518 | 1305 | Conversion specifiers are introduced by a @samp{%} character, followed |
a2b08ee5 | 1306 | by an optional flag which can be one of the following. These flags |
cf822e3c | 1307 | are all GNU extensions. The first three affect only the output of |
a2b08ee5 | 1308 | numbers: |
2de99474 UD |
1309 | |
1310 | @table @code | |
1311 | @item _ | |
1312 | The number is padded with spaces. | |
1313 | ||
1314 | @item - | |
1315 | The number is not padded at all. | |
860d3729 UD |
1316 | |
1317 | @item 0 | |
7e3be507 | 1318 | The number is padded with zeros even if the format specifies padding |
860d3729 | 1319 | with spaces. |
7e3be507 UD |
1320 | |
1321 | @item ^ | |
1322 | The output uses uppercase characters, but only if this is possible | |
1323 | (@pxref{Case Conversion}). | |
2de99474 UD |
1324 | @end table |
1325 | ||
ec4b0518 UD |
1326 | The default action is to pad the number with zeros to keep it a constant |
1327 | width. Numbers that do not have a range indicated below are never | |
1328 | padded, since there is no natural width for them. | |
1329 | ||
860d3729 UD |
1330 | Following the flag an optional specification of the width is possible. |
1331 | This is specified in decimal notation. If the natural size of the | |
9269924c | 1332 | output of the field has less than the specified number of characters, |
860d3729 UD |
1333 | the result is written right adjusted and space padded to the given |
1334 | size. | |
1335 | ||
1336 | An optional modifier can follow the optional flag and width | |
ba737b94 UD |
1337 | specification. The modifiers, which were first standardized by |
1338 | POSIX.2-1992 and by @w{ISO C99}, are: | |
ec4b0518 UD |
1339 | |
1340 | @table @code | |
1341 | @item E | |
80dfa298 | 1342 | Use the locale's alternative representation for date and time. This |
ec4b0518 UD |
1343 | modifier applies to the @code{%c}, @code{%C}, @code{%x}, @code{%X}, |
1344 | @code{%y} and @code{%Y} format specifiers. In a Japanese locale, for | |
1345 | example, @code{%Ex} might yield a date format based on the Japanese | |
1346 | Emperors' reigns. | |
1347 | ||
1348 | @item O | |
22390764 | 1349 | With all format specifiers that produce numbers: use the locale's |
80dfa298 | 1350 | alternative numeric symbols. |
22390764 | 1351 | |
0f5e2da1 RJ |
1352 | With @code{%B}, @code{%b}, and @code{%h}: use the grammatical form for |
1353 | month names that is appropriate when the month is named by itself, | |
1354 | rather than the form that is appropriate when the month is used as | |
c737ef0d JM |
1355 | part of a complete date. The @code{%OB} and @code{%Ob} formats are a |
1356 | C2X feature, specified in C2X to use the locale's `alternative' month | |
1357 | name; @theglibc{} extends this specification to say that the form used | |
1358 | in a complete date is the default and the form naming the month by | |
1359 | itself is the alternative. | |
ec4b0518 UD |
1360 | @end table |
1361 | ||
80dfa298 | 1362 | If the format supports the modifier but no alternative representation |
860d3729 | 1363 | is available, it is ignored. |
ec4b0518 UD |
1364 | |
1365 | The conversion specifier ends with a format specifier taken from the | |
1366 | following list. The whole @samp{%} sequence is replaced in the output | |
1367 | string as follows: | |
28f540f4 RM |
1368 | |
1369 | @table @code | |
1370 | @item %a | |
1371 | The abbreviated weekday name according to the current locale. | |
1372 | ||
1373 | @item %A | |
1374 | The full weekday name according to the current locale. | |
1375 | ||
1376 | @item %b | |
22390764 RL |
1377 | The abbreviated month name according to the current locale, in the |
1378 | grammatical form used when the month is part of a complete date. | |
c737ef0d JM |
1379 | As a C2X feature (with a more detailed specification in @theglibc{}), |
1380 | the @code{O} modifier can be used (@code{%Ob}) to get the grammatical | |
1381 | form used when the month is named by itself. | |
28f540f4 RM |
1382 | |
1383 | @item %B | |
22390764 RL |
1384 | The full month name according to the current locale, in the |
1385 | grammatical form used when the month is part of a complete date. | |
c737ef0d JM |
1386 | As a C2X feature (with a more detailed specification in @theglibc{}), |
1387 | the @code{O} modifier can be used (@code{%OB}) to get the grammatical | |
1388 | form used when the month is named by itself. | |
28f540f4 | 1389 | |
22390764 RL |
1390 | Note that not all languages need two different forms of the month |
1391 | names, so the text produced by @code{%B} and @code{%OB}, and by | |
1392 | @code{%b} and @code{%Ob}, may or may not be the same, depending on | |
1393 | the locale. | |
c093ea4f | 1394 | |
28f540f4 | 1395 | @item %c |
99a20616 | 1396 | The preferred calendar time representation for the current locale. |
28f540f4 | 1397 | |
2de99474 | 1398 | @item %C |
ec4b0518 UD |
1399 | The century of the year. This is equivalent to the greatest integer not |
1400 | greater than the year divided by 100. | |
1401 | ||
32f600a2 TS |
1402 | If the @code{E} modifier is specified (@code{%EC}), instead produces |
1403 | the name of the period for the year (e.g.@: an era name) in the | |
1404 | locale's alternative calendar. | |
1405 | ||
ba737b94 | 1406 | This format was first standardized by POSIX.2-1992 and by @w{ISO C99}. |
2de99474 | 1407 | |
28f540f4 | 1408 | @item %d |
ec4b0518 | 1409 | The day of the month as a decimal number (range @code{01} through @code{31}). |
28f540f4 | 1410 | |
2de99474 UD |
1411 | @item %D |
1412 | The date using the format @code{%m/%d/%y}. | |
1413 | ||
ba737b94 | 1414 | This format was first standardized by POSIX.2-1992 and by @w{ISO C99}. |
2de99474 | 1415 | |
ec4b0518 | 1416 | @item %e |
9269924c | 1417 | The day of the month like with @code{%d}, but padded with spaces (range |
ec4b0518 UD |
1418 | @code{ 1} through @code{31}). |
1419 | ||
ba737b94 | 1420 | This format was first standardized by POSIX.2-1992 and by @w{ISO C99}. |
ec4b0518 | 1421 | |
fe0ec73e UD |
1422 | @item %F |
1423 | The date using the format @code{%Y-%m-%d}. This is the form specified | |
1424 | in the @w{ISO 8601} standard and is the preferred form for all uses. | |
1425 | ||
ba737b94 | 1426 | This format was first standardized by @w{ISO C99} and by POSIX.1-2001. |
fe0ec73e | 1427 | |
ec4b0518 UD |
1428 | @item %g |
1429 | The year corresponding to the ISO week number, but without the century | |
1430 | (range @code{00} through @code{99}). This has the same format and value | |
1431 | as @code{%y}, except that if the ISO week number (see @code{%V}) belongs | |
1432 | to the previous or next year, that year is used instead. | |
1433 | ||
ba737b94 | 1434 | This format was first standardized by @w{ISO C99} and by POSIX.1-2001. |
ec4b0518 UD |
1435 | |
1436 | @item %G | |
1437 | The year corresponding to the ISO week number. This has the same format | |
1438 | and value as @code{%Y}, except that if the ISO week number (see | |
1439 | @code{%V}) belongs to the previous or next year, that year is used | |
1440 | instead. | |
2de99474 | 1441 | |
ba737b94 UD |
1442 | This format was first standardized by @w{ISO C99} and by POSIX.1-2001 |
1443 | but was previously available as a GNU extension. | |
2de99474 UD |
1444 | |
1445 | @item %h | |
1446 | The abbreviated month name according to the current locale. The action | |
1447 | is the same as for @code{%b}. | |
1448 | ||
ba737b94 | 1449 | This format was first standardized by POSIX.2-1992 and by @w{ISO C99}. |
2de99474 | 1450 | |
28f540f4 | 1451 | @item %H |
ec4b0518 | 1452 | The hour as a decimal number, using a 24-hour clock (range @code{00} through |
28f540f4 RM |
1453 | @code{23}). |
1454 | ||
1455 | @item %I | |
ec4b0518 | 1456 | The hour as a decimal number, using a 12-hour clock (range @code{01} through |
28f540f4 RM |
1457 | @code{12}). |
1458 | ||
1459 | @item %j | |
ec4b0518 | 1460 | The day of the year as a decimal number (range @code{001} through @code{366}). |
28f540f4 | 1461 | |
2de99474 UD |
1462 | @item %k |
1463 | The hour as a decimal number, using a 24-hour clock like @code{%H}, but | |
9269924c | 1464 | padded with spaces (range @code{ 0} through @code{23}). |
2de99474 UD |
1465 | |
1466 | This format is a GNU extension. | |
1467 | ||
1468 | @item %l | |
1469 | The hour as a decimal number, using a 12-hour clock like @code{%I}, but | |
9269924c | 1470 | padded with spaces (range @code{ 1} through @code{12}). |
2de99474 UD |
1471 | |
1472 | This format is a GNU extension. | |
1473 | ||
28f540f4 | 1474 | @item %m |
ec4b0518 | 1475 | The month as a decimal number (range @code{01} through @code{12}). |
28f540f4 RM |
1476 | |
1477 | @item %M | |
ec4b0518 | 1478 | The minute as a decimal number (range @code{00} through @code{59}). |
28f540f4 | 1479 | |
2de99474 UD |
1480 | @item %n |
1481 | A single @samp{\n} (newline) character. | |
1482 | ||
ba737b94 | 1483 | This format was first standardized by POSIX.2-1992 and by @w{ISO C99}. |
2de99474 | 1484 | |
28f540f4 | 1485 | @item %p |
ec4b0518 UD |
1486 | Either @samp{AM} or @samp{PM}, according to the given time value; or the |
1487 | corresponding strings for the current locale. Noon is treated as | |
eabea972 UD |
1488 | @samp{PM} and midnight as @samp{AM}. In most locales |
1489 | @samp{AM}/@samp{PM} format is not supported, in such cases @code{"%p"} | |
1490 | yields an empty string. | |
28f540f4 | 1491 | |
7e3be507 UD |
1492 | @ignore |
1493 | We currently have a problem with makeinfo. Write @samp{AM} and @samp{am} | |
1494 | both results in `am'. I.e., the difference in case is not visible anymore. | |
1495 | @end ignore | |
1496 | @item %P | |
1497 | Either @samp{am} or @samp{pm}, according to the given time value; or the | |
1498 | corresponding strings for the current locale, printed in lowercase | |
eabea972 UD |
1499 | characters. Noon is treated as @samp{pm} and midnight as @samp{am}. In |
1500 | most locales @samp{AM}/@samp{PM} format is not supported, in such cases | |
1501 | @code{"%P"} yields an empty string. | |
7e3be507 | 1502 | |
ba737b94 | 1503 | This format is a GNU extension. |
7e3be507 | 1504 | |
2de99474 | 1505 | @item %r |
99a20616 | 1506 | The complete calendar time using the AM/PM format of the current locale. |
2de99474 | 1507 | |
ba737b94 UD |
1508 | This format was first standardized by POSIX.2-1992 and by @w{ISO C99}. |
1509 | In the POSIX locale, this format is equivalent to @code{%I:%M:%S %p}. | |
2de99474 UD |
1510 | |
1511 | @item %R | |
1512 | The hour and minute in decimal numbers using the format @code{%H:%M}. | |
1513 | ||
ba737b94 UD |
1514 | This format was first standardized by @w{ISO C99} and by POSIX.1-2001 |
1515 | but was previously available as a GNU extension. | |
2de99474 UD |
1516 | |
1517 | @item %s | |
ec4b0518 UD |
1518 | The number of seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC. |
1519 | Leap seconds are not counted unless leap second support is available. | |
2de99474 UD |
1520 | |
1521 | This format is a GNU extension. | |
1522 | ||
28f540f4 | 1523 | @item %S |
e9dcb080 | 1524 | The seconds as a decimal number (range @code{00} through @code{60}). |
28f540f4 | 1525 | |
2de99474 UD |
1526 | @item %t |
1527 | A single @samp{\t} (tabulator) character. | |
1528 | ||
ba737b94 | 1529 | This format was first standardized by POSIX.2-1992 and by @w{ISO C99}. |
2de99474 UD |
1530 | |
1531 | @item %T | |
99a20616 | 1532 | The time of day using decimal numbers using the format @code{%H:%M:%S}. |
2de99474 | 1533 | |
ba737b94 | 1534 | This format was first standardized by POSIX.2-1992 and by @w{ISO C99}. |
ec4b0518 UD |
1535 | |
1536 | @item %u | |
1537 | The day of the week as a decimal number (range @code{1} through | |
1538 | @code{7}), Monday being @code{1}. | |
1539 | ||
ba737b94 | 1540 | This format was first standardized by POSIX.2-1992 and by @w{ISO C99}. |
2de99474 | 1541 | |
28f540f4 | 1542 | @item %U |
ec4b0518 UD |
1543 | The week number of the current year as a decimal number (range @code{00} |
1544 | through @code{53}), starting with the first Sunday as the first day of | |
1545 | the first week. Days preceding the first Sunday in the year are | |
1546 | considered to be in week @code{00}. | |
7c713e28 RM |
1547 | |
1548 | @item %V | |
ec4b0518 UD |
1549 | The @w{ISO 8601:1988} week number as a decimal number (range @code{01} |
1550 | through @code{53}). ISO weeks start with Monday and end with Sunday. | |
1551 | Week @code{01} of a year is the first week which has the majority of its | |
1552 | days in that year; this is equivalent to the week containing the year's | |
1553 | first Thursday, and it is also equivalent to the week containing January | |
1554 | 4. Week @code{01} of a year can contain days from the previous year. | |
1555 | The week before week @code{01} of a year is the last week (@code{52} or | |
1556 | @code{53}) of the previous year even if it contains days from the new | |
1557 | year. | |
1558 | ||
ba737b94 | 1559 | This format was first standardized by POSIX.2-1992 and by @w{ISO C99}. |
28f540f4 | 1560 | |
2de99474 | 1561 | @item %w |
ec4b0518 UD |
1562 | The day of the week as a decimal number (range @code{0} through |
1563 | @code{6}), Sunday being @code{0}. | |
2de99474 | 1564 | |
28f540f4 | 1565 | @item %W |
ec4b0518 UD |
1566 | The week number of the current year as a decimal number (range @code{00} |
1567 | through @code{53}), starting with the first Monday as the first day of | |
1568 | the first week. All days preceding the first Monday in the year are | |
1569 | considered to be in week @code{00}. | |
28f540f4 | 1570 | |
28f540f4 | 1571 | @item %x |
99a20616 | 1572 | The preferred date representation for the current locale. |
28f540f4 RM |
1573 | |
1574 | @item %X | |
99a20616 | 1575 | The preferred time of day representation for the current locale. |
28f540f4 RM |
1576 | |
1577 | @item %y | |
ec4b0518 UD |
1578 | The year without a century as a decimal number (range @code{00} through |
1579 | @code{99}). This is equivalent to the year modulo 100. | |
28f540f4 | 1580 | |
b22eed37 TS |
1581 | If the @code{E} modifier is specified (@code{%Ey}), instead produces |
1582 | the year number according to a locale-specific alternative calendar. | |
1583 | Unlike @code{%y}, the number is @emph{not} reduced modulo 100. | |
1584 | However, by default it is zero-padded to a minimum of two digits (this | |
1585 | can be overridden by an explicit field width or by the @code{_} and | |
1586 | @code{-} flags). | |
1587 | ||
28f540f4 | 1588 | @item %Y |
ec4b0518 UD |
1589 | The year as a decimal number, using the Gregorian calendar. Years |
1590 | before the year @code{1} are numbered @code{0}, @code{-1}, and so on. | |
28f540f4 | 1591 | |
32f600a2 TS |
1592 | If the @code{E} modifier is specified (@code{%EY}), instead produces a |
1593 | complete representation of the year according to the locale's | |
1594 | alternative calendar. Generally this will be some combination of the | |
10dd69e9 TS |
1595 | information produced by @code{%EC} and @code{%Ey}. As a GNU |
1596 | extension, the formatting flags @code{_} or @code{-} may be used with | |
1597 | this conversion specifier; they affect how the year number is printed. | |
32f600a2 | 1598 | |
2de99474 | 1599 | @item %z |
f0f1bf85 UD |
1600 | @w{RFC 822}/@w{ISO 8601:1988} style numeric time zone (e.g., |
1601 | @code{-0600} or @code{+0100}), or nothing if no time zone is | |
1602 | determinable. | |
2de99474 | 1603 | |
ba737b94 UD |
1604 | This format was first standardized by @w{ISO C99} and by POSIX.1-2001 |
1605 | but was previously available as a GNU extension. | |
ec4b0518 | 1606 | |
ba737b94 | 1607 | In the POSIX locale, a full @w{RFC 822} timestamp is generated by the format |
e9dcb080 | 1608 | @w{@samp{"%a, %d %b %Y %H:%M:%S %z"}} (or the equivalent |
eeabe877 | 1609 | @w{@samp{"%a, %d %b %Y %T %z"}}). |
e1350332 | 1610 | |
28f540f4 | 1611 | @item %Z |
ec4b0518 | 1612 | The time zone abbreviation (empty if the time zone can't be determined). |
28f540f4 RM |
1613 | |
1614 | @item %% | |
1615 | A literal @samp{%} character. | |
1616 | @end table | |
1617 | ||
1618 | The @var{size} parameter can be used to specify the maximum number of | |
1619 | characters to be stored in the array @var{s}, including the terminating | |
1620 | null character. If the formatted time requires more than @var{size} | |
76c23bac UD |
1621 | characters, @code{strftime} returns zero and the contents of the array |
1622 | @var{s} are undefined. Otherwise the return value indicates the | |
55c14926 UD |
1623 | number of characters placed in the array @var{s}, not including the |
1624 | terminating null character. | |
1625 | ||
1626 | @emph{Warning:} This convention for the return value which is prescribed | |
1627 | in @w{ISO C} can lead to problems in some situations. For certain | |
1628 | format strings and certain locales the output really can be the empty | |
1629 | string and this cannot be discovered by testing the return value only. | |
1630 | E.g., in most locales the AM/PM time format is not supported (most of | |
1631 | the world uses the 24 hour time representation). In such locales | |
1632 | @code{"%p"} will return the empty string, i.e., the return value is | |
1633 | zero. To detect situations like this something similar to the following | |
1634 | code should be used: | |
1635 | ||
1636 | @smallexample | |
1637 | buf[0] = '\1'; | |
1638 | len = strftime (buf, bufsize, format, tp); | |
1639 | if (len == 0 && buf[0] != '\0') | |
1640 | @{ | |
1641 | /* Something went wrong in the strftime call. */ | |
1642 | @dots{} | |
1643 | @} | |
1644 | @end smallexample | |
28f540f4 RM |
1645 | |
1646 | If @var{s} is a null pointer, @code{strftime} does not actually write | |
1647 | anything, but instead returns the number of characters it would have written. | |
1648 | ||
fbf964ae PE |
1649 | Calling @code{strftime} also sets the current time zone as if |
1650 | @code{tzset} were called; @code{strftime} uses this information | |
1651 | instead of @var{brokentime}'s @code{tm_gmtoff} and @code{tm_zone} | |
1652 | members. @xref{Time Zone Functions}. | |
860d3729 | 1653 | |
28f540f4 RM |
1654 | For an example of @code{strftime}, see @ref{Time Functions Example}. |
1655 | @end deftypefun | |
1656 | ||
d64b6ad0 | 1657 | @deftypefun size_t wcsftime (wchar_t *@var{s}, size_t @var{size}, const wchar_t *@var{template}, const struct tm *@var{brokentime}) |
d08a7e4c | 1658 | @standards{ISO/Amend1, time.h} |
23e5b8cb AO |
1659 | @safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}} |
1660 | @c wcsftime @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd | |
1661 | @c wcsftime_l @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd | |
1662 | @c wcsftime_internal @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd | |
1663 | @c add ok | |
1664 | @c memset_zero dup ok | |
1665 | @c memset_space dup ok | |
1666 | @c wcslen dup ok | |
1667 | @c cpy ok | |
1668 | @c add dup ok | |
1669 | @c memcpy_lowcase ok | |
1670 | @c TOLOWER ok | |
1671 | @c towlower_l dup ok | |
1672 | @c memcpy_uppcase ok | |
1673 | @c TOUPPER ok | |
1674 | @c towupper_l dup ok | |
1675 | @c MEMCPY ok | |
1676 | @c wmemcpy dup ok | |
1677 | @c widen @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd | |
1678 | @c memset dup ok | |
1679 | @c mbsrtowcs_l @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd [no @mtasurace:mbstate/!ps] | |
1680 | @c ISDIGIT ok | |
1681 | @c STRLEN ok | |
1682 | @c wcslen dup ok | |
1683 | @c wcsftime_internal dup @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd | |
1684 | @c TOUPPER dup ok | |
1685 | @c nl_get_era_entry dup @ascuheap @asulock @acsmem @aculock | |
1686 | @c DO_NUMBER ok | |
1687 | @c DO_NUMBER_SPACEPAD ok | |
1688 | @c nl_get_walt_digit dup @ascuheap @asulock @acsmem @aculock | |
1689 | @c libc_rwlock_wrlock dup @asulock @aculock | |
1690 | @c nl_init_alt_digit dup @ascuheap @acsmem | |
1691 | @c malloc dup @ascuheap @acsmem | |
1692 | @c memset dup ok | |
1693 | @c wcschr dup ok | |
1694 | @c libc_rwlock_unlock dup @aculock | |
1695 | @c memset_space ok | |
1696 | @c wmemset dup ok | |
1697 | @c memset_zero ok | |
1698 | @c wmemset dup ok | |
1699 | @c mktime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1700 | @c iso_week_days ok | |
1701 | @c isleap ok | |
1702 | @c tzset dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1703 | @c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1704 | @c gmtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1705 | @c tm_diff ok | |
d64b6ad0 | 1706 | The @code{wcsftime} function is equivalent to the @code{strftime} |
76c23bac | 1707 | function with the difference that it operates on wide character |
d64b6ad0 UD |
1708 | strings. The buffer where the result is stored, pointed to by @var{s}, |
1709 | must be an array of wide characters. The parameter @var{size} which | |
1710 | specifies the size of the output buffer gives the number of wide | |
9269924c | 1711 | characters, not the number of bytes. |
d64b6ad0 UD |
1712 | |
1713 | Also the format string @var{template} is a wide character string. Since | |
1714 | all characters needed to specify the format string are in the basic | |
76c23bac | 1715 | character set it is portably possible to write format strings in the C |
95fdc6a0 | 1716 | source code using the @code{L"@dots{}"} notation. The parameter |
d64b6ad0 UD |
1717 | @var{brokentime} has the same meaning as in the @code{strftime} call. |
1718 | ||
1719 | The @code{wcsftime} function supports the same flags, modifiers, and | |
1720 | format specifiers as the @code{strftime} function. | |
1721 | ||
1722 | The return value of @code{wcsftime} is the number of wide characters | |
1723 | stored in @code{s}. When more characters would have to be written than | |
1724 | can be placed in the buffer @var{s} the return value is zero, with the | |
1725 | same problems indicated in the @code{strftime} documentation. | |
1726 | @end deftypefun | |
1727 | ||
e9dcb080 UD |
1728 | @node Parsing Date and Time |
1729 | @subsection Convert textual time and date information back | |
1730 | ||
1731 | The @w{ISO C} standard does not specify any functions which can convert | |
1732 | the output of the @code{strftime} function back into a binary format. | |
76c23bac UD |
1733 | This led to a variety of more-or-less successful implementations with |
1734 | different interfaces over the years. Then the Unix standard was | |
1735 | extended by the addition of two functions: @code{strptime} and | |
1736 | @code{getdate}. Both have strange interfaces but at least they are | |
1737 | widely available. | |
e9dcb080 UD |
1738 | |
1739 | @menu | |
1740 | * Low-Level Time String Parsing:: Interpret string according to given format. | |
1741 | * General Time String Parsing:: User-friendly function to parse data and | |
1742 | time strings. | |
1743 | @end menu | |
1744 | ||
1745 | @node Low-Level Time String Parsing | |
1746 | @subsubsection Interpret string according to given format | |
1747 | ||
11bf311e | 1748 | The first function is rather low-level. It is nevertheless frequently |
76c23bac UD |
1749 | used in software since it is better known. Its interface and |
1750 | implementation are heavily influenced by the @code{getdate} function, | |
1751 | which is defined and implemented in terms of calls to @code{strptime}. | |
e9dcb080 | 1752 | |
e9dcb080 | 1753 | @deftypefun {char *} strptime (const char *@var{s}, const char *@var{fmt}, struct tm *@var{tp}) |
d08a7e4c | 1754 | @standards{XPG4, time.h} |
23e5b8cb AO |
1755 | @safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
1756 | @c strptime @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1757 | @c strptime_internal @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1758 | @c memset dup ok | |
1759 | @c ISSPACE ok | |
1760 | @c isspace_l dup ok | |
1761 | @c match_char ok | |
1762 | @c match_string ok | |
1763 | @c strlen dup ok | |
1764 | @c strncasecmp_l dup ok | |
1765 | @c strcmp dup ok | |
1766 | @c recursive @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1767 | @c strptime_internal dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1768 | @c get_number ok | |
1769 | @c ISSPACE dup ok | |
1770 | @c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
1771 | @c nl_select_era_entry @ascuheap @asulock @acsmem @aculock | |
1772 | @c nl_init_era_entries dup @ascuheap @asulock @acsmem @aculock | |
1773 | @c get_alt_number dup @ascuheap @asulock @acsmem @aculock | |
1774 | @c nl_parse_alt_digit dup @ascuheap @asulock @acsmem @aculock | |
1775 | @c libc_rwlock_wrlock dup @asulock @aculock | |
1776 | @c nl_init_alt_digit dup @ascuheap @acsmem | |
1777 | @c libc_rwlock_unlock dup @aculock | |
1778 | @c get_number dup ok | |
1779 | @c day_of_the_week ok | |
1780 | @c day_of_the_year ok | |
e9dcb080 | 1781 | The @code{strptime} function parses the input string @var{s} according |
76c23bac | 1782 | to the format string @var{fmt} and stores its results in the |
e9dcb080 UD |
1783 | structure @var{tp}. |
1784 | ||
76c23bac UD |
1785 | The input string could be generated by a @code{strftime} call or |
1786 | obtained any other way. It does not need to be in a human-recognizable | |
1787 | format; e.g. a date passed as @code{"02:1999:9"} is acceptable, even | |
1788 | though it is ambiguous without context. As long as the format string | |
1789 | @var{fmt} matches the input string the function will succeed. | |
e9dcb080 | 1790 | |
45e0579f UD |
1791 | The user has to make sure, though, that the input can be parsed in a |
1792 | unambiguous way. The string @code{"1999112"} can be parsed using the | |
1793 | format @code{"%Y%m%d"} as 1999-1-12, 1999-11-2, or even 19991-1-2. It | |
1794 | is necessary to add appropriate separators to reliably get results. | |
1795 | ||
e9dcb080 | 1796 | The format string consists of the same components as the format string |
76c23bac | 1797 | of the @code{strftime} function. The only difference is that the flags |
e9dcb080 UD |
1798 | @code{_}, @code{-}, @code{0}, and @code{^} are not allowed. |
1799 | @comment Is this really the intention? --drepper | |
76c23bac UD |
1800 | Several of the distinct formats of @code{strftime} do the same work in |
1801 | @code{strptime} since differences like case of the input do not matter. | |
1802 | For reasons of symmetry all formats are supported, though. | |
e9dcb080 UD |
1803 | |
1804 | The modifiers @code{E} and @code{O} are also allowed everywhere the | |
1805 | @code{strftime} function allows them. | |
1806 | ||
1807 | The formats are: | |
1808 | ||
1809 | @table @code | |
1810 | @item %a | |
1811 | @itemx %A | |
1812 | The weekday name according to the current locale, in abbreviated form or | |
1813 | the full name. | |
1814 | ||
1815 | @item %b | |
1816 | @itemx %B | |
1817 | @itemx %h | |
22390764 RL |
1818 | A month name according to the current locale. All three specifiers |
1819 | will recognize both abbreviated and full month names. If the | |
1820 | locale provides two different grammatical forms of month names, | |
1821 | all three specifiers will recognize both forms. | |
1822 | ||
1823 | As a GNU extension, the @code{O} modifier can be used with these | |
1824 | specifiers; it has no effect, as both grammatical forms of month | |
1825 | names are recognized. | |
e9dcb080 UD |
1826 | |
1827 | @item %c | |
1828 | The date and time representation for the current locale. | |
1829 | ||
1830 | @item %Ec | |
1831 | Like @code{%c} but the locale's alternative date and time format is used. | |
1832 | ||
1833 | @item %C | |
1834 | The century of the year. | |
1835 | ||
1836 | It makes sense to use this format only if the format string also | |
1837 | contains the @code{%y} format. | |
1838 | ||
1839 | @item %EC | |
1840 | The locale's representation of the period. | |
1841 | ||
76c23bac UD |
1842 | Unlike @code{%C} it sometimes makes sense to use this format since some |
1843 | cultures represent years relative to the beginning of eras instead of | |
1844 | using the Gregorian years. | |
e9dcb080 UD |
1845 | |
1846 | @item %d | |
1847 | @item %e | |
1848 | The day of the month as a decimal number (range @code{1} through @code{31}). | |
1849 | Leading zeroes are permitted but not required. | |
1850 | ||
1851 | @item %Od | |
1852 | @itemx %Oe | |
76c23bac | 1853 | Same as @code{%d} but using the locale's alternative numeric symbols. |
e9dcb080 UD |
1854 | |
1855 | Leading zeroes are permitted but not required. | |
1856 | ||
1857 | @item %D | |
76c23bac | 1858 | Equivalent to @code{%m/%d/%y}. |
e9dcb080 UD |
1859 | |
1860 | @item %F | |
76c23bac | 1861 | Equivalent to @code{%Y-%m-%d}, which is the @w{ISO 8601} date |
e9dcb080 UD |
1862 | format. |
1863 | ||
ec751a23 | 1864 | This is a GNU extension following an @w{ISO C99} extension to |
e9dcb080 UD |
1865 | @code{strftime}. |
1866 | ||
1867 | @item %g | |
1868 | The year corresponding to the ISO week number, but without the century | |
1869 | (range @code{00} through @code{99}). | |
1870 | ||
76c23bac | 1871 | @emph{Note:} Currently, this is not fully implemented. The format is |
e9dcb080 UD |
1872 | recognized, input is consumed but no field in @var{tm} is set. |
1873 | ||
1874 | This format is a GNU extension following a GNU extension of @code{strftime}. | |
1875 | ||
1876 | @item %G | |
1877 | The year corresponding to the ISO week number. | |
1878 | ||
76c23bac | 1879 | @emph{Note:} Currently, this is not fully implemented. The format is |
e9dcb080 UD |
1880 | recognized, input is consumed but no field in @var{tm} is set. |
1881 | ||
1882 | This format is a GNU extension following a GNU extension of @code{strftime}. | |
1883 | ||
1884 | @item %H | |
1885 | @itemx %k | |
1886 | The hour as a decimal number, using a 24-hour clock (range @code{00} through | |
1887 | @code{23}). | |
1888 | ||
1889 | @code{%k} is a GNU extension following a GNU extension of @code{strftime}. | |
1890 | ||
1891 | @item %OH | |
76c23bac | 1892 | Same as @code{%H} but using the locale's alternative numeric symbols. |
e9dcb080 UD |
1893 | |
1894 | @item %I | |
1895 | @itemx %l | |
1896 | The hour as a decimal number, using a 12-hour clock (range @code{01} through | |
1897 | @code{12}). | |
1898 | ||
1899 | @code{%l} is a GNU extension following a GNU extension of @code{strftime}. | |
1900 | ||
1901 | @item %OI | |
76c23bac | 1902 | Same as @code{%I} but using the locale's alternative numeric symbols. |
e9dcb080 UD |
1903 | |
1904 | @item %j | |
1905 | The day of the year as a decimal number (range @code{1} through @code{366}). | |
1906 | ||
1907 | Leading zeroes are permitted but not required. | |
1908 | ||
1909 | @item %m | |
1910 | The month as a decimal number (range @code{1} through @code{12}). | |
1911 | ||
1912 | Leading zeroes are permitted but not required. | |
1913 | ||
1914 | @item %Om | |
76c23bac | 1915 | Same as @code{%m} but using the locale's alternative numeric symbols. |
e9dcb080 UD |
1916 | |
1917 | @item %M | |
1918 | The minute as a decimal number (range @code{0} through @code{59}). | |
1919 | ||
1920 | Leading zeroes are permitted but not required. | |
1921 | ||
1922 | @item %OM | |
76c23bac | 1923 | Same as @code{%M} but using the locale's alternative numeric symbols. |
e9dcb080 UD |
1924 | |
1925 | @item %n | |
1926 | @itemx %t | |
1927 | Matches any white space. | |
1928 | ||
1929 | @item %p | |
1930 | @item %P | |
1931 | The locale-dependent equivalent to @samp{AM} or @samp{PM}. | |
1932 | ||
1933 | This format is not useful unless @code{%I} or @code{%l} is also used. | |
1934 | Another complication is that the locale might not define these values at | |
1935 | all and therefore the conversion fails. | |
1936 | ||
1937 | @code{%P} is a GNU extension following a GNU extension to @code{strftime}. | |
1938 | ||
1939 | @item %r | |
1940 | The complete time using the AM/PM format of the current locale. | |
1941 | ||
1942 | A complication is that the locale might not define this format at all | |
1943 | and therefore the conversion fails. | |
1944 | ||
1945 | @item %R | |
1946 | The hour and minute in decimal numbers using the format @code{%H:%M}. | |
1947 | ||
1948 | @code{%R} is a GNU extension following a GNU extension to @code{strftime}. | |
1949 | ||
1950 | @item %s | |
1951 | The number of seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC. | |
1952 | Leap seconds are not counted unless leap second support is available. | |
1953 | ||
1954 | @code{%s} is a GNU extension following a GNU extension to @code{strftime}. | |
1955 | ||
1956 | @item %S | |
99a20616 | 1957 | The seconds as a decimal number (range @code{0} through @code{60}). |
e9dcb080 UD |
1958 | |
1959 | Leading zeroes are permitted but not required. | |
1960 | ||
48b22986 | 1961 | @strong{NB:} The Unix specification says the upper bound on this value |
99a20616 UD |
1962 | is @code{61}, a result of a decision to allow double leap seconds. You |
1963 | will not see the value @code{61} because no minute has more than one | |
1964 | leap second, but the myth persists. | |
e9dcb080 UD |
1965 | |
1966 | @item %OS | |
76c23bac | 1967 | Same as @code{%S} but using the locale's alternative numeric symbols. |
e9dcb080 UD |
1968 | |
1969 | @item %T | |
1970 | Equivalent to the use of @code{%H:%M:%S} in this place. | |
1971 | ||
1972 | @item %u | |
1973 | The day of the week as a decimal number (range @code{1} through | |
1974 | @code{7}), Monday being @code{1}. | |
1975 | ||
1976 | Leading zeroes are permitted but not required. | |
1977 | ||
76c23bac | 1978 | @emph{Note:} Currently, this is not fully implemented. The format is |
e9dcb080 UD |
1979 | recognized, input is consumed but no field in @var{tm} is set. |
1980 | ||
1981 | @item %U | |
1982 | The week number of the current year as a decimal number (range @code{0} | |
1983 | through @code{53}). | |
1984 | ||
1985 | Leading zeroes are permitted but not required. | |
1986 | ||
1987 | @item %OU | |
76c23bac | 1988 | Same as @code{%U} but using the locale's alternative numeric symbols. |
e9dcb080 UD |
1989 | |
1990 | @item %V | |
1991 | The @w{ISO 8601:1988} week number as a decimal number (range @code{1} | |
1992 | through @code{53}). | |
1993 | ||
1994 | Leading zeroes are permitted but not required. | |
1995 | ||
76c23bac | 1996 | @emph{Note:} Currently, this is not fully implemented. The format is |
e9dcb080 UD |
1997 | recognized, input is consumed but no field in @var{tm} is set. |
1998 | ||
1999 | @item %w | |
2000 | The day of the week as a decimal number (range @code{0} through | |
2001 | @code{6}), Sunday being @code{0}. | |
2002 | ||
2003 | Leading zeroes are permitted but not required. | |
2004 | ||
76c23bac | 2005 | @emph{Note:} Currently, this is not fully implemented. The format is |
e9dcb080 UD |
2006 | recognized, input is consumed but no field in @var{tm} is set. |
2007 | ||
2008 | @item %Ow | |
76c23bac | 2009 | Same as @code{%w} but using the locale's alternative numeric symbols. |
e9dcb080 UD |
2010 | |
2011 | @item %W | |
2012 | The week number of the current year as a decimal number (range @code{0} | |
2013 | through @code{53}). | |
2014 | ||
2015 | Leading zeroes are permitted but not required. | |
2016 | ||
76c23bac | 2017 | @emph{Note:} Currently, this is not fully implemented. The format is |
e9dcb080 UD |
2018 | recognized, input is consumed but no field in @var{tm} is set. |
2019 | ||
2020 | @item %OW | |
76c23bac | 2021 | Same as @code{%W} but using the locale's alternative numeric symbols. |
e9dcb080 UD |
2022 | |
2023 | @item %x | |
2024 | The date using the locale's date format. | |
2025 | ||
2026 | @item %Ex | |
2027 | Like @code{%x} but the locale's alternative data representation is used. | |
2028 | ||
2029 | @item %X | |
2030 | The time using the locale's time format. | |
2031 | ||
2032 | @item %EX | |
2033 | Like @code{%X} but the locale's alternative time representation is used. | |
2034 | ||
2035 | @item %y | |
2036 | The year without a century as a decimal number (range @code{0} through | |
2037 | @code{99}). | |
2038 | ||
2039 | Leading zeroes are permitted but not required. | |
2040 | ||
76c23bac | 2041 | Note that it is questionable to use this format without |
e9dcb080 UD |
2042 | the @code{%C} format. The @code{strptime} function does regard input |
2043 | values in the range @math{68} to @math{99} as the years @math{1969} to | |
2044 | @math{1999} and the values @math{0} to @math{68} as the years | |
2045 | @math{2000} to @math{2068}. But maybe this heuristic fails for some | |
2046 | input data. | |
2047 | ||
2048 | Therefore it is best to avoid @code{%y} completely and use @code{%Y} | |
2049 | instead. | |
2050 | ||
2051 | @item %Ey | |
2052 | The offset from @code{%EC} in the locale's alternative representation. | |
2053 | ||
2054 | @item %Oy | |
2055 | The offset of the year (from @code{%C}) using the locale's alternative | |
2056 | numeric symbols. | |
2057 | ||
2058 | @item %Y | |
2059 | The year as a decimal number, using the Gregorian calendar. | |
2060 | ||
2061 | @item %EY | |
2062 | The full alternative year representation. | |
2063 | ||
2064 | @item %z | |
107d41a9 | 2065 | The offset from GMT in @w{ISO 8601}/RFC822 format. |
e9dcb080 UD |
2066 | |
2067 | @item %Z | |
2068 | The timezone name. | |
2069 | ||
76c23bac | 2070 | @emph{Note:} Currently, this is not fully implemented. The format is |
e9dcb080 UD |
2071 | recognized, input is consumed but no field in @var{tm} is set. |
2072 | ||
2073 | @item %% | |
2074 | A literal @samp{%} character. | |
2075 | @end table | |
2076 | ||
2077 | All other characters in the format string must have a matching character | |
2078 | in the input string. Exceptions are white spaces in the input string | |
05957bbd UD |
2079 | which can match zero or more whitespace characters in the format string. |
2080 | ||
2081 | @strong{Portability Note:} The XPG standard advises applications to use | |
2082 | at least one whitespace character (as specified by @code{isspace}) or | |
2083 | other non-alphanumeric characters between any two conversion | |
1f77f049 | 2084 | specifications. @Theglibc{} does not have this limitation but |
05957bbd UD |
2085 | other libraries might have trouble parsing formats like |
2086 | @code{"%d%m%Y%H%M%S"}. | |
e9dcb080 UD |
2087 | |
2088 | The @code{strptime} function processes the input string from right to | |
2089 | left. Each of the three possible input elements (white space, literal, | |
2090 | or format) are handled one after the other. If the input cannot be | |
2091 | matched to the format string the function stops. The remainder of the | |
2092 | format and input strings are not processed. | |
2093 | ||
76c23bac UD |
2094 | The function returns a pointer to the first character it was unable to |
2095 | process. If the input string contains more characters than required by | |
2096 | the format string the return value points right after the last consumed | |
2097 | input character. If the whole input string is consumed the return value | |
2098 | points to the @code{NULL} byte at the end of the string. If an error | |
11bf311e | 2099 | occurs, i.e., @code{strptime} fails to match all of the format string, |
76c23bac | 2100 | the function returns @code{NULL}. |
e9dcb080 UD |
2101 | @end deftypefun |
2102 | ||
76c23bac UD |
2103 | The specification of the function in the XPG standard is rather vague, |
2104 | leaving out a few important pieces of information. Most importantly, it | |
e9dcb080 | 2105 | does not specify what happens to those elements of @var{tm} which are |
76c23bac | 2106 | not directly initialized by the different formats. The |
e9dcb080 UD |
2107 | implementations on different Unix systems vary here. |
2108 | ||
1f77f049 | 2109 | The @glibcadj{} implementation does not touch those fields which are not |
e9dcb080 | 2110 | directly initialized. Exceptions are the @code{tm_wday} and |
76c23bac | 2111 | @code{tm_yday} elements, which are recomputed if any of the year, month, |
e9dcb080 UD |
2112 | or date elements changed. This has two implications: |
2113 | ||
2114 | @itemize @bullet | |
2115 | @item | |
76c23bac UD |
2116 | Before calling the @code{strptime} function for a new input string, you |
2117 | should prepare the @var{tm} structure you pass. Normally this will mean | |
9269924c | 2118 | initializing all values to zero. Alternatively, you can set all |
76c23bac UD |
2119 | fields to values like @code{INT_MAX}, allowing you to determine which |
2120 | elements were set by the function call. Zero does not work here since | |
2121 | it is a valid value for many of the fields. | |
2122 | ||
2123 | Careful initialization is necessary if you want to find out whether a | |
e9dcb080 UD |
2124 | certain field in @var{tm} was initialized by the function call. |
2125 | ||
2126 | @item | |
76c23bac UD |
2127 | You can construct a @code{struct tm} value with several consecutive |
2128 | @code{strptime} calls. A useful application of this is e.g. the parsing | |
2129 | of two separate strings, one containing date information and the other | |
2130 | time information. By parsing one after the other without clearing the | |
2131 | structure in-between, you can construct a complete broken-down time. | |
e9dcb080 UD |
2132 | @end itemize |
2133 | ||
9269924c | 2134 | The following example shows a function which parses a string which |
76c23bac | 2135 | contains the date information in either US style or @w{ISO 8601} form: |
e9dcb080 UD |
2136 | |
2137 | @smallexample | |
2138 | const char * | |
2139 | parse_date (const char *input, struct tm *tm) | |
2140 | @{ | |
2141 | const char *cp; | |
2142 | ||
2143 | /* @r{First clear the result structure.} */ | |
2144 | memset (tm, '\0', sizeof (*tm)); | |
2145 | ||
2146 | /* @r{Try the ISO format first.} */ | |
2147 | cp = strptime (input, "%F", tm); | |
2148 | if (cp == NULL) | |
2149 | @{ | |
2150 | /* @r{Does not match. Try the US form.} */ | |
2151 | cp = strptime (input, "%D", tm); | |
2152 | @} | |
2153 | ||
2154 | return cp; | |
2155 | @} | |
2156 | @end smallexample | |
2157 | ||
2158 | @node General Time String Parsing | |
76c23bac | 2159 | @subsubsection A More User-friendly Way to Parse Times and Dates |
e9dcb080 | 2160 | |
76c23bac UD |
2161 | The Unix standard defines another function for parsing date strings. |
2162 | The interface is weird, but if the function happens to suit your | |
2163 | application it is just fine. It is problematic to use this function | |
2164 | in multi-threaded programs or libraries, since it returns a pointer to | |
2165 | a static variable, and uses a global variable and global state (an | |
2166 | environment variable). | |
e9dcb080 | 2167 | |
e9dcb080 | 2168 | @defvar getdate_err |
d08a7e4c | 2169 | @standards{Unix98, time.h} |
76c23bac UD |
2170 | This variable of type @code{int} contains the error code of the last |
2171 | unsuccessful call to @code{getdate}. Defined values are: | |
e9dcb080 UD |
2172 | |
2173 | @table @math | |
2174 | @item 1 | |
2175 | The environment variable @code{DATEMSK} is not defined or null. | |
2176 | @item 2 | |
2177 | The template file denoted by the @code{DATEMSK} environment variable | |
2178 | cannot be opened. | |
2179 | @item 3 | |
2180 | Information about the template file cannot retrieved. | |
2181 | @item 4 | |
76c23bac | 2182 | The template file is not a regular file. |
e9dcb080 UD |
2183 | @item 5 |
2184 | An I/O error occurred while reading the template file. | |
2185 | @item 6 | |
2186 | Not enough memory available to execute the function. | |
2187 | @item 7 | |
2188 | The template file contains no matching template. | |
2189 | @item 8 | |
76c23bac UD |
2190 | The input date is invalid, but would match a template otherwise. This |
2191 | includes dates like February 31st, and dates which cannot be represented | |
2192 | in a @code{time_t} variable. | |
e9dcb080 UD |
2193 | @end table |
2194 | @end defvar | |
2195 | ||
e9dcb080 | 2196 | @deftypefun {struct tm *} getdate (const char *@var{string}) |
d08a7e4c | 2197 | @standards{Unix98, time.h} |
23e5b8cb AO |
2198 | @safety{@prelim{}@mtunsafe{@mtasurace{:getdate} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
2199 | @c getdate @mtasurace:getdate @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
2200 | @c getdate_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
76c23bac UD |
2201 | The interface to @code{getdate} is the simplest possible for a function |
2202 | to parse a string and return the value. @var{string} is the input | |
2203 | string and the result is returned in a statically-allocated variable. | |
e9dcb080 | 2204 | |
76c23bac UD |
2205 | The details about how the string is processed are hidden from the user. |
2206 | In fact, they can be outside the control of the program. Which formats | |
e9dcb080 | 2207 | are recognized is controlled by the file named by the environment |
76c23bac | 2208 | variable @code{DATEMSK}. This file should contain |
e9dcb080 UD |
2209 | lines of valid format strings which could be passed to @code{strptime}. |
2210 | ||
2211 | The @code{getdate} function reads these format strings one after the | |
2212 | other and tries to match the input string. The first line which | |
2213 | completely matches the input string is used. | |
2214 | ||
76c23bac UD |
2215 | Elements not initialized through the format string retain the values |
2216 | present at the time of the @code{getdate} function call. | |
e9dcb080 | 2217 | |
76c23bac | 2218 | The formats recognized by @code{getdate} are the same as for |
e9dcb080 | 2219 | @code{strptime}. See above for an explanation. There are only a few |
76c23bac | 2220 | extensions to the @code{strptime} behavior: |
e9dcb080 UD |
2221 | |
2222 | @itemize @bullet | |
2223 | @item | |
2224 | If the @code{%Z} format is given the broken-down time is based on the | |
76c23bac | 2225 | current time of the timezone matched, not of the current timezone of the |
e9dcb080 UD |
2226 | runtime environment. |
2227 | ||
2228 | @emph{Note}: This is not implemented (currently). The problem is that | |
2229 | timezone names are not unique. If a fixed timezone is assumed for a | |
76c23bac | 2230 | given string (say @code{EST} meaning US East Coast time), then uses for |
e9dcb080 | 2231 | countries other than the USA will fail. So far we have found no good |
76c23bac | 2232 | solution to this. |
e9dcb080 UD |
2233 | |
2234 | @item | |
2235 | If only the weekday is specified the selected day depends on the current | |
9269924c | 2236 | date. If the current weekday is greater than or equal to the @code{tm_wday} |
76c23bac | 2237 | value the current week's day is chosen, otherwise the day next week is chosen. |
e9dcb080 UD |
2238 | |
2239 | @item | |
76c23bac UD |
2240 | A similar heuristic is used when only the month is given and not the |
2241 | year. If the month is greater than or equal to the current month, then | |
2242 | the current year is used. Otherwise it wraps to next year. The first | |
2243 | day of the month is assumed if one is not explicitly specified. | |
e9dcb080 UD |
2244 | |
2245 | @item | |
76c23bac | 2246 | The current hour, minute, and second are used if the appropriate value is |
e9dcb080 UD |
2247 | not set through the format. |
2248 | ||
2249 | @item | |
76c23bac UD |
2250 | If no date is given tomorrow's date is used if the time is |
2251 | smaller than the current time. Otherwise today's date is taken. | |
e9dcb080 UD |
2252 | @end itemize |
2253 | ||
2254 | It should be noted that the format in the template file need not only | |
2255 | contain format elements. The following is a list of possible format | |
2256 | strings (taken from the Unix standard): | |
2257 | ||
2258 | @smallexample | |
2259 | %m | |
2260 | %A %B %d, %Y %H:%M:%S | |
2261 | %A | |
2262 | %B | |
2263 | %m/%d/%y %I %p | |
2264 | %d,%m,%Y %H:%M | |
2265 | at %A the %dst of %B in %Y | |
2266 | run job at %I %p,%B %dnd | |
2267 | %A den %d. %B %Y %H.%M Uhr | |
2268 | @end smallexample | |
2269 | ||
76c23bac | 2270 | As you can see, the template list can contain very specific strings like |
e9dcb080 | 2271 | @code{run job at %I %p,%B %dnd}. Using the above list of templates and |
9269924c | 2272 | assuming the current time is Mon Sep 22 12:19:47 EDT 1986, we can obtain the |
16a8520f | 2273 | following results for the given input. |
e9dcb080 | 2274 | |
16a8520f | 2275 | @multitable {xxxxxxxxxxxx} {xxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} |
76c23bac | 2276 | @item Input @tab Match @tab Result |
e9dcb080 UD |
2277 | @item Mon @tab %a @tab Mon Sep 22 12:19:47 EDT 1986 |
2278 | @item Sun @tab %a @tab Sun Sep 28 12:19:47 EDT 1986 | |
2279 | @item Fri @tab %a @tab Fri Sep 26 12:19:47 EDT 1986 | |
2280 | @item September @tab %B @tab Mon Sep 1 12:19:47 EDT 1986 | |
2281 | @item January @tab %B @tab Thu Jan 1 12:19:47 EST 1987 | |
2282 | @item December @tab %B @tab Mon Dec 1 12:19:47 EST 1986 | |
2283 | @item Sep Mon @tab %b %a @tab Mon Sep 1 12:19:47 EDT 1986 | |
2284 | @item Jan Fri @tab %b %a @tab Fri Jan 2 12:19:47 EST 1987 | |
2285 | @item Dec Mon @tab %b %a @tab Mon Dec 1 12:19:47 EST 1986 | |
2286 | @item Jan Wed 1989 @tab %b %a %Y @tab Wed Jan 4 12:19:47 EST 1989 | |
2287 | @item Fri 9 @tab %a %H @tab Fri Sep 26 09:00:00 EDT 1986 | |
2288 | @item Feb 10:30 @tab %b %H:%S @tab Sun Feb 1 10:00:30 EST 1987 | |
2289 | @item 10:30 @tab %H:%M @tab Tue Sep 23 10:30:00 EDT 1986 | |
2290 | @item 13:30 @tab %H:%M @tab Mon Sep 22 13:30:00 EDT 1986 | |
2291 | @end multitable | |
2292 | ||
2293 | The return value of the function is a pointer to a static variable of | |
76c23bac UD |
2294 | type @w{@code{struct tm}}, or a null pointer if an error occurred. The |
2295 | result is only valid until the next @code{getdate} call, making this | |
2296 | function unusable in multi-threaded applications. | |
e9dcb080 UD |
2297 | |
2298 | The @code{errno} variable is @emph{not} changed. Error conditions are | |
76c23bac | 2299 | stored in the global variable @code{getdate_err}. See the |
e9dcb080 | 2300 | description above for a list of the possible error values. |
c730d678 UD |
2301 | |
2302 | @emph{Warning:} The @code{getdate} function should @emph{never} be | |
2303 | used in SUID-programs. The reason is obvious: using the | |
76c23bac | 2304 | @code{DATEMSK} environment variable you can get the function to open |
16a8520f | 2305 | any arbitrary file and chances are high that with some bogus input |
c730d678 UD |
2306 | (such as a binary file) the program will crash. |
2307 | @end deftypefun | |
2308 | ||
c730d678 | 2309 | @deftypefun int getdate_r (const char *@var{string}, struct tm *@var{tp}) |
d08a7e4c | 2310 | @standards{GNU, time.h} |
23e5b8cb AO |
2311 | @safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
2312 | @c getdate_r @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
2313 | @c getenv dup @mtsenv | |
2314 | @c stat64 dup ok | |
2315 | @c access dup ok | |
2316 | @c fopen dup @ascuheap @asulock @acsmem @acsfd @aculock | |
2317 | @c fsetlocking dup ok [no @mtasurace:stream @asulock, exclusive] | |
2318 | @c isspace dup @mtslocale | |
2319 | @c strlen dup ok | |
2320 | @c malloc dup @ascuheap @acsmem | |
2321 | @c fclose dup @ascuheap @asulock @aculock @acsmem @acsfd | |
2322 | @c memcpy dup ok | |
2323 | @c getline dup @ascuheap @acsmem [no @asucorrupt @aculock @acucorrupt, exclusive] | |
2324 | @c strptime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
2325 | @c feof_unlocked dup ok | |
2326 | @c free dup @ascuheap @acsmem | |
2327 | @c ferror_unlocked dup dup ok | |
2328 | @c time dup ok | |
2329 | @c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
2330 | @c first_wday @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
2331 | @c memset dup ok | |
2332 | @c mktime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
2333 | @c check_mday ok | |
2334 | @c mktime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
c730d678 UD |
2335 | The @code{getdate_r} function is the reentrant counterpart of |
2336 | @code{getdate}. It does not use the global variable @code{getdate_err} | |
76c23bac UD |
2337 | to signal an error, but instead returns an error code. The same error |
2338 | codes as described in the @code{getdate_err} documentation above are | |
2339 | used, with 0 meaning success. | |
c730d678 | 2340 | |
76c23bac UD |
2341 | Moreover, @code{getdate_r} stores the broken-down time in the variable |
2342 | of type @code{struct tm} pointed to by the second argument, rather than | |
2343 | in a static variable. | |
c730d678 UD |
2344 | |
2345 | This function is not defined in the Unix standard. Nevertheless it is | |
2346 | available on some other Unix systems as well. | |
2347 | ||
76c23bac UD |
2348 | The warning against using @code{getdate} in SUID-programs applies to |
2349 | @code{getdate_r} as well. | |
e9dcb080 UD |
2350 | @end deftypefun |
2351 | ||
28f540f4 RM |
2352 | @node TZ Variable |
2353 | @subsection Specifying the Time Zone with @code{TZ} | |
2354 | ||
2355 | In POSIX systems, a user can specify the time zone by means of the | |
2356 | @code{TZ} environment variable. For information about how to set | |
2357 | environment variables, see @ref{Environment Variables}. The functions | |
2358 | for accessing the time zone are declared in @file{time.h}. | |
2359 | @pindex time.h | |
2360 | @cindex time zone | |
2361 | ||
2362 | You should not normally need to set @code{TZ}. If the system is | |
f0f1bf85 | 2363 | configured properly, the default time zone will be correct. You might |
76c23bac UD |
2364 | set @code{TZ} if you are using a computer over a network from a |
2365 | different time zone, and would like times reported to you in the time | |
2366 | zone local to you, rather than what is local to the computer. | |
28f540f4 | 2367 | |
76c23bac | 2368 | In POSIX.1 systems the value of the @code{TZ} variable can be in one of |
1f77f049 | 2369 | three formats. With @theglibc{}, the most common format is the |
28f540f4 RM |
2370 | last one, which can specify a selection from a large database of time |
2371 | zone information for many regions of the world. The first two formats | |
2372 | are used to describe the time zone information directly, which is both | |
2373 | more cumbersome and less precise. But the POSIX.1 standard only | |
2374 | specifies the details of the first two formats, so it is good to be | |
2375 | familiar with them in case you come across a POSIX.1 system that doesn't | |
2376 | support a time zone information database. | |
2377 | ||
2378 | The first format is used when there is no Daylight Saving Time (or | |
2379 | summer time) in the local time zone: | |
2380 | ||
2381 | @smallexample | |
2382 | @r{@var{std} @var{offset}} | |
2383 | @end smallexample | |
2384 | ||
2385 | The @var{std} string specifies the name of the time zone. It must be | |
76c23bac UD |
2386 | three or more characters long and must not contain a leading colon, |
2387 | embedded digits, commas, nor plus and minus signs. There is no space | |
28f540f4 RM |
2388 | character separating the time zone name from the @var{offset}, so these |
2389 | restrictions are necessary to parse the specification correctly. | |
2390 | ||
76c23bac | 2391 | The @var{offset} specifies the time value you must add to the local time |
28f540f4 RM |
2392 | to get a Coordinated Universal Time value. It has syntax like |
2393 | [@code{+}|@code{-}]@var{hh}[@code{:}@var{mm}[@code{:}@var{ss}]]. This | |
2394 | is positive if the local time zone is west of the Prime Meridian and | |
2395 | negative if it is east. The hour must be between @code{0} and | |
674762d9 | 2396 | @code{24}, and the minute and seconds between @code{0} and @code{59}. |
28f540f4 RM |
2397 | |
2398 | For example, here is how we would specify Eastern Standard Time, but | |
76c23bac | 2399 | without any Daylight Saving Time alternative: |
28f540f4 RM |
2400 | |
2401 | @smallexample | |
2402 | EST+5 | |
2403 | @end smallexample | |
2404 | ||
2405 | The second format is used when there is Daylight Saving Time: | |
2406 | ||
2407 | @smallexample | |
2408 | @r{@var{std} @var{offset} @var{dst} [@var{offset}]@code{,}@var{start}[@code{/}@var{time}]@code{,}@var{end}[@code{/}@var{time}]} | |
2409 | @end smallexample | |
2410 | ||
2411 | The initial @var{std} and @var{offset} specify the standard time zone, as | |
2412 | described above. The @var{dst} string and @var{offset} specify the name | |
76c23bac | 2413 | and offset for the corresponding Daylight Saving Time zone; if the |
28f540f4 RM |
2414 | @var{offset} is omitted, it defaults to one hour ahead of standard time. |
2415 | ||
76c23bac UD |
2416 | The remainder of the specification describes when Daylight Saving Time is |
2417 | in effect. The @var{start} field is when Daylight Saving Time goes into | |
28f540f4 RM |
2418 | effect and the @var{end} field is when the change is made back to standard |
2419 | time. The following formats are recognized for these fields: | |
2420 | ||
2421 | @table @code | |
2422 | @item J@var{n} | |
2423 | This specifies the Julian day, with @var{n} between @code{1} and @code{365}. | |
2424 | February 29 is never counted, even in leap years. | |
2425 | ||
2426 | @item @var{n} | |
2427 | This specifies the Julian day, with @var{n} between @code{0} and @code{365}. | |
2428 | February 29 is counted in leap years. | |
2429 | ||
2430 | @item M@var{m}.@var{w}.@var{d} | |
2431 | This specifies day @var{d} of week @var{w} of month @var{m}. The day | |
2432 | @var{d} must be between @code{0} (Sunday) and @code{6}. The week | |
2433 | @var{w} must be between @code{1} and @code{5}; week @code{1} is the | |
2434 | first week in which day @var{d} occurs, and week @code{5} specifies the | |
2435 | @emph{last} @var{d} day in the month. The month @var{m} should be | |
2436 | between @code{1} and @code{12}. | |
2437 | @end table | |
2438 | ||
2439 | The @var{time} fields specify when, in the local time currently in | |
2440 | effect, the change to the other time occurs. If omitted, the default is | |
4480e934 | 2441 | @code{02:00:00}. The hours part of the time fields can range from |
0748546f | 2442 | @minus{}167 through 167; this is an extension to POSIX.1, which allows |
4480e934 | 2443 | only the range 0 through 24. |
28f540f4 | 2444 | |
4480e934 | 2445 | Here are some example @code{TZ} values, including the appropriate |
69947401 PE |
2446 | Daylight Saving Time and its dates of applicability. In North |
2447 | American Eastern Standard Time (EST) and Eastern Daylight Time (EDT), | |
2448 | the normal offset from UTC is 5 hours; since this is | |
28f540f4 | 2449 | west of the prime meridian, the sign is positive. Summer time begins on |
69947401 | 2450 | March's second Sunday at 2:00am, and ends on November's first Sunday |
28f540f4 RM |
2451 | at 2:00am. |
2452 | ||
2453 | @smallexample | |
69947401 | 2454 | EST+5EDT,M3.2.0/2,M11.1.0/2 |
28f540f4 RM |
2455 | @end smallexample |
2456 | ||
4480e934 PE |
2457 | Israel Standard Time (IST) and Israel Daylight Time (IDT) are 2 hours |
2458 | ahead of the prime meridian in winter, springing forward an hour on | |
f3a4632a | 2459 | March's fourth Thursday at 26:00 (i.e., 02:00 on the first Friday on or |
4480e934 PE |
2460 | after March 23), and falling back on October's last Sunday at 02:00. |
2461 | ||
2462 | @smallexample | |
2463 | IST-2IDT,M3.4.4/26,M10.5.0 | |
2464 | @end smallexample | |
2465 | ||
2466 | Western Argentina Summer Time (WARST) is 3 hours behind the prime | |
2467 | meridian all year. There is a dummy fall-back transition on December | |
2468 | 31 at 25:00 daylight saving time (i.e., 24:00 standard time, | |
2469 | equivalent to January 1 at 00:00 standard time), and a simultaneous | |
2470 | spring-forward transition on January 1 at 00:00 standard time, so | |
2471 | daylight saving time is in effect all year and the initial @code{WART} | |
2472 | is a placeholder. | |
2473 | ||
2474 | @smallexample | |
2475 | WART4WARST,J1/0,J365/25 | |
2476 | @end smallexample | |
2477 | ||
0748546f PE |
2478 | Western Greenland Time (WGT) and Western Greenland Summer Time (WGST) |
2479 | are 3 hours behind UTC in the winter. Its clocks follow the European | |
2480 | Union rules of springing forward by one hour on March's last Sunday at | |
2481 | 01:00 UTC (@minus{}02:00 local time) and falling back on October's | |
2482 | last Sunday at 01:00 UTC (@minus{}01:00 local time). | |
2483 | ||
2484 | @smallexample | |
2485 | WGT3WGST,M3.5.0/-2,M10.5.0/-1 | |
2486 | @end smallexample | |
2487 | ||
76c23bac | 2488 | The schedule of Daylight Saving Time in any particular jurisdiction has |
28f540f4 RM |
2489 | changed over the years. To be strictly correct, the conversion of dates |
2490 | and times in the past should be based on the schedule that was in effect | |
2491 | then. However, this format has no facilities to let you specify how the | |
2492 | schedule has changed from year to year. The most you can do is specify | |
2493 | one particular schedule---usually the present day schedule---and this is | |
2494 | used to convert any date, no matter when. For precise time zone | |
2495 | specifications, it is best to use the time zone information database | |
2496 | (see below). | |
2497 | ||
2498 | The third format looks like this: | |
2499 | ||
2500 | @smallexample | |
2501 | :@var{characters} | |
2502 | @end smallexample | |
2503 | ||
1f77f049 JM |
2504 | Each operating system interprets this format differently; in |
2505 | @theglibc{}, @var{characters} is the name of a file which describes the time | |
28f540f4 RM |
2506 | zone. |
2507 | ||
2508 | @pindex /etc/localtime | |
2509 | @pindex localtime | |
2510 | If the @code{TZ} environment variable does not have a value, the | |
1f77f049 | 2511 | operation chooses a time zone by default. In @theglibc{}, the |
28f540f4 | 2512 | default time zone is like the specification @samp{TZ=:/etc/localtime} |
1f77f049 | 2513 | (or @samp{TZ=:/usr/local/etc/localtime}, depending on how @theglibc{} |
28f540f4 RM |
2514 | was configured; @pxref{Installation}). Other C libraries use their own |
2515 | rule for choosing the default time zone, so there is little we can say | |
2516 | about them. | |
2517 | ||
2518 | @cindex time zone database | |
3f293d61 | 2519 | @pindex /usr/share/zoneinfo |
28f540f4 RM |
2520 | @pindex zoneinfo |
2521 | If @var{characters} begins with a slash, it is an absolute file name; | |
2522 | otherwise the library looks for the file | |
3f293d61 | 2523 | @w{@file{/usr/share/zoneinfo/@var{characters}}}. The @file{zoneinfo} |
28f540f4 RM |
2524 | directory contains data files describing local time zones in many |
2525 | different parts of the world. The names represent major cities, with | |
2526 | subdirectories for geographical areas; for example, | |
2527 | @file{America/New_York}, @file{Europe/London}, @file{Asia/Hong_Kong}. | |
2528 | These data files are installed by the system administrator, who also | |
2529 | sets @file{/etc/localtime} to point to the data file for the local time | |
0d7036bd PE |
2530 | zone. The files typically come from the @url{http://www.iana.org/time-zones, |
2531 | Time Zone Database} of time zone and daylight saving time | |
28f540f4 RM |
2532 | information for most regions of the world, which is maintained by a |
2533 | community of volunteers and put in the public domain. | |
2534 | ||
2535 | @node Time Zone Functions | |
2536 | @subsection Functions and Variables for Time Zones | |
2537 | ||
2c6fe0bd | 2538 | @deftypevar {char *} tzname [2] |
d08a7e4c | 2539 | @standards{POSIX.1, time.h} |
28f540f4 | 2540 | The array @code{tzname} contains two strings, which are the standard |
76c23bac UD |
2541 | names of the pair of time zones (standard and Daylight |
2542 | Saving) that the user has selected. @code{tzname[0]} is the name of | |
28f540f4 | 2543 | the standard time zone (for example, @code{"EST"}), and @code{tzname[1]} |
76c23bac | 2544 | is the name for the time zone when Daylight Saving Time is in use (for |
28f540f4 | 2545 | example, @code{"EDT"}). These correspond to the @var{std} and @var{dst} |
f0f1bf85 | 2546 | strings (respectively) from the @code{TZ} environment variable. If |
76c23bac | 2547 | Daylight Saving Time is never used, @code{tzname[1]} is the empty string. |
28f540f4 RM |
2548 | |
2549 | The @code{tzname} array is initialized from the @code{TZ} environment | |
2550 | variable whenever @code{tzset}, @code{ctime}, @code{strftime}, | |
f0f1bf85 UD |
2551 | @code{mktime}, or @code{localtime} is called. If multiple abbreviations |
2552 | have been used (e.g. @code{"EWT"} and @code{"EDT"} for U.S. Eastern War | |
2553 | Time and Eastern Daylight Time), the array contains the most recent | |
2554 | abbreviation. | |
2555 | ||
2556 | The @code{tzname} array is required for POSIX.1 compatibility, but in | |
2557 | GNU programs it is better to use the @code{tm_zone} member of the | |
2558 | broken-down time structure, since @code{tm_zone} reports the correct | |
2559 | abbreviation even when it is not the latest one. | |
2560 | ||
76c23bac | 2561 | Though the strings are declared as @code{char *} the user must refrain |
f2ea0f5b | 2562 | from modifying these strings. Modifying the strings will almost certainly |
0413b54c UD |
2563 | lead to trouble. |
2564 | ||
28f540f4 RM |
2565 | @end deftypevar |
2566 | ||
28f540f4 | 2567 | @deftypefun void tzset (void) |
d08a7e4c | 2568 | @standards{POSIX.1, time.h} |
23e5b8cb AO |
2569 | @safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}} |
2570 | @c tzset @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
2571 | @c libc_lock_lock dup @asulock @aculock | |
2572 | @c tzset_internal dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd | |
2573 | @c libc_lock_unlock dup @aculock | |
28f540f4 RM |
2574 | The @code{tzset} function initializes the @code{tzname} variable from |
2575 | the value of the @code{TZ} environment variable. It is not usually | |
2576 | necessary for your program to call this function, because it is called | |
2577 | automatically when you use the other time conversion functions that | |
2578 | depend on the time zone. | |
2579 | @end deftypefun | |
2580 | ||
2581 | The following variables are defined for compatibility with System V | |
f0f1bf85 UD |
2582 | Unix. Like @code{tzname}, these variables are set by calling |
2583 | @code{tzset} or the other time conversion functions. | |
28f540f4 | 2584 | |
28f540f4 | 2585 | @deftypevar {long int} timezone |
d08a7e4c | 2586 | @standards{SVID, time.h} |
f0f1bf85 UD |
2587 | This contains the difference between UTC and the latest local standard |
2588 | time, in seconds west of UTC. For example, in the U.S. Eastern time | |
2589 | zone, the value is @code{5*60*60}. Unlike the @code{tm_gmtoff} member | |
2590 | of the broken-down time structure, this value is not adjusted for | |
2591 | daylight saving, and its sign is reversed. In GNU programs it is better | |
2592 | to use @code{tm_gmtoff}, since it contains the correct offset even when | |
2593 | it is not the latest one. | |
28f540f4 RM |
2594 | @end deftypevar |
2595 | ||
28f540f4 | 2596 | @deftypevar int daylight |
d08a7e4c | 2597 | @standards{SVID, time.h} |
76c23bac UD |
2598 | This variable has a nonzero value if Daylight Saving Time rules apply. |
2599 | A nonzero value does not necessarily mean that Daylight Saving Time is | |
2600 | now in effect; it means only that Daylight Saving Time is sometimes in | |
60092701 | 2601 | effect. |
28f540f4 RM |
2602 | @end deftypevar |
2603 | ||
2604 | @node Time Functions Example | |
2605 | @subsection Time Functions Example | |
2606 | ||
3566d33c UD |
2607 | Here is an example program showing the use of some of the calendar time |
2608 | functions. | |
28f540f4 RM |
2609 | |
2610 | @smallexample | |
2611 | @include strftim.c.texi | |
2612 | @end smallexample | |
2613 | ||
2614 | It produces output like this: | |
2615 | ||
2616 | @smallexample | |
2617 | Wed Jul 31 13:02:36 1991 | |
2618 | Today is Wednesday, July 31. | |
2619 | The time is 01:02 PM. | |
2620 | @end smallexample | |
2621 | ||
2622 | ||
2623 | @node Setting an Alarm | |
2624 | @section Setting an Alarm | |
2625 | ||
2626 | The @code{alarm} and @code{setitimer} functions provide a mechanism for a | |
99a20616 | 2627 | process to interrupt itself in the future. They do this by setting a |
28f540f4 RM |
2628 | timer; when the timer expires, the process receives a signal. |
2629 | ||
2630 | @cindex setting an alarm | |
2631 | @cindex interval timer, setting | |
2632 | @cindex alarms, setting | |
2633 | @cindex timers, setting | |
2634 | Each process has three independent interval timers available: | |
2635 | ||
2636 | @itemize @bullet | |
01cdeca0 | 2637 | @item |
99a20616 | 2638 | A real-time timer that counts elapsed time. This timer sends a |
28f540f4 RM |
2639 | @code{SIGALRM} signal to the process when it expires. |
2640 | @cindex real-time timer | |
2641 | @cindex timer, real-time | |
2642 | ||
01cdeca0 | 2643 | @item |
99a20616 | 2644 | A virtual timer that counts processor time used by the process. This timer |
28f540f4 RM |
2645 | sends a @code{SIGVTALRM} signal to the process when it expires. |
2646 | @cindex virtual timer | |
2647 | @cindex timer, virtual | |
2648 | ||
01cdeca0 | 2649 | @item |
99a20616 UD |
2650 | A profiling timer that counts both processor time used by the process, |
2651 | and processor time spent in system calls on behalf of the process. This | |
2652 | timer sends a @code{SIGPROF} signal to the process when it expires. | |
28f540f4 RM |
2653 | @cindex profiling timer |
2654 | @cindex timer, profiling | |
2655 | ||
2656 | This timer is useful for profiling in interpreters. The interval timer | |
2657 | mechanism does not have the fine granularity necessary for profiling | |
2658 | native code. | |
2659 | @c @xref{profil} !!! | |
2660 | @end itemize | |
2661 | ||
2662 | You can only have one timer of each kind set at any given time. If you | |
2663 | set a timer that has not yet expired, that timer is simply reset to the | |
2664 | new value. | |
2665 | ||
2666 | You should establish a handler for the appropriate alarm signal using | |
76c23bac UD |
2667 | @code{signal} or @code{sigaction} before issuing a call to |
2668 | @code{setitimer} or @code{alarm}. Otherwise, an unusual chain of events | |
2669 | could cause the timer to expire before your program establishes the | |
2670 | handler. In this case it would be terminated, since termination is the | |
2671 | default action for the alarm signals. @xref{Signal Handling}. | |
28f540f4 | 2672 | |
f51dadcc UD |
2673 | To be able to use the alarm function to interrupt a system call which |
2674 | might block otherwise indefinitely it is important to @emph{not} set the | |
2675 | @code{SA_RESTART} flag when registering the signal handler using | |
2676 | @code{sigaction}. When not using @code{sigaction} things get even | |
9269924c | 2677 | uglier: the @code{signal} function has fixed semantics with respect |
f51dadcc UD |
2678 | to restarts. The BSD semantics for this function is to set the flag. |
2679 | Therefore, if @code{sigaction} for whatever reason cannot be used, it is | |
2680 | necessary to use @code{sysv_signal} and not @code{signal}. | |
2681 | ||
28f540f4 RM |
2682 | The @code{setitimer} function is the primary means for setting an alarm. |
2683 | This facility is declared in the header file @file{sys/time.h}. The | |
2684 | @code{alarm} function, declared in @file{unistd.h}, provides a somewhat | |
2685 | simpler interface for setting the real-time timer. | |
2686 | @pindex unistd.h | |
2687 | @pindex sys/time.h | |
2688 | ||
28f540f4 | 2689 | @deftp {Data Type} {struct itimerval} |
d08a7e4c | 2690 | @standards{BSD, sys/time.h} |
28f540f4 RM |
2691 | This structure is used to specify when a timer should expire. It contains |
2692 | the following members: | |
2693 | @table @code | |
2694 | @item struct timeval it_interval | |
99a20616 | 2695 | This is the period between successive timer interrupts. If zero, the |
28f540f4 RM |
2696 | alarm will only be sent once. |
2697 | ||
2698 | @item struct timeval it_value | |
99a20616 UD |
2699 | This is the period between now and the first timer interrupt. If zero, |
2700 | the alarm is disabled. | |
28f540f4 RM |
2701 | @end table |
2702 | ||
99a20616 | 2703 | The @code{struct timeval} data type is described in @ref{Elapsed Time}. |
28f540f4 RM |
2704 | @end deftp |
2705 | ||
8ded91fb | 2706 | @deftypefun int setitimer (int @var{which}, const struct itimerval *@var{new}, struct itimerval *@var{old}) |
d08a7e4c | 2707 | @standards{BSD, sys/time.h} |
23e5b8cb AO |
2708 | @safety{@prelim{}@mtsafe{@mtstimer{}}@assafe{}@acsafe{}} |
2709 | @c This function is marked with @mtstimer because the same set of timers | |
2710 | @c is shared by all threads of a process, so calling it in one thread | |
2711 | @c may interfere with timers set by another thread. This interference | |
2712 | @c is not regarded as destructive, because the interface specification | |
2713 | @c makes this overriding while returning the previous value the expected | |
2714 | @c behavior, and the kernel will serialize concurrent calls so that the | |
2715 | @c last one prevails, with each call getting the timer information from | |
2716 | @c the timer installed by the previous call in that serialization. | |
01cdeca0 | 2717 | The @code{setitimer} function sets the timer specified by @var{which} |
28f540f4 RM |
2718 | according to @var{new}. The @var{which} argument can have a value of |
2719 | @code{ITIMER_REAL}, @code{ITIMER_VIRTUAL}, or @code{ITIMER_PROF}. | |
2720 | ||
2721 | If @var{old} is not a null pointer, @code{setitimer} returns information | |
2722 | about any previous unexpired timer of the same kind in the structure it | |
2723 | points to. | |
2724 | ||
2725 | The return value is @code{0} on success and @code{-1} on failure. The | |
2726 | following @code{errno} error conditions are defined for this function: | |
2727 | ||
2728 | @table @code | |
2729 | @item EINVAL | |
99a20616 | 2730 | The timer period is too large. |
28f540f4 RM |
2731 | @end table |
2732 | @end deftypefun | |
2733 | ||
28f540f4 | 2734 | @deftypefun int getitimer (int @var{which}, struct itimerval *@var{old}) |
d08a7e4c | 2735 | @standards{BSD, sys/time.h} |
23e5b8cb | 2736 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
28f540f4 RM |
2737 | The @code{getitimer} function stores information about the timer specified |
2738 | by @var{which} in the structure pointed at by @var{old}. | |
2739 | ||
2740 | The return value and error conditions are the same as for @code{setitimer}. | |
2741 | @end deftypefun | |
2742 | ||
f227c3e0 | 2743 | @vtable @code |
28f540f4 | 2744 | @item ITIMER_REAL |
d08a7e4c | 2745 | @standards{BSD, sys/time.h} |
28f540f4 RM |
2746 | This constant can be used as the @var{which} argument to the |
2747 | @code{setitimer} and @code{getitimer} functions to specify the real-time | |
2748 | timer. | |
2749 | ||
28f540f4 | 2750 | @item ITIMER_VIRTUAL |
d08a7e4c | 2751 | @standards{BSD, sys/time.h} |
28f540f4 RM |
2752 | This constant can be used as the @var{which} argument to the |
2753 | @code{setitimer} and @code{getitimer} functions to specify the virtual | |
2754 | timer. | |
2755 | ||
28f540f4 | 2756 | @item ITIMER_PROF |
d08a7e4c | 2757 | @standards{BSD, sys/time.h} |
28f540f4 RM |
2758 | This constant can be used as the @var{which} argument to the |
2759 | @code{setitimer} and @code{getitimer} functions to specify the profiling | |
2760 | timer. | |
b642f101 | 2761 | @end vtable |
28f540f4 | 2762 | |
28f540f4 | 2763 | @deftypefun {unsigned int} alarm (unsigned int @var{seconds}) |
d08a7e4c | 2764 | @standards{POSIX.1, unistd.h} |
23e5b8cb AO |
2765 | @safety{@prelim{}@mtsafe{@mtstimer{}}@assafe{}@acsafe{}} |
2766 | @c Wrapper for setitimer. | |
28f540f4 RM |
2767 | The @code{alarm} function sets the real-time timer to expire in |
2768 | @var{seconds} seconds. If you want to cancel any existing alarm, you | |
2769 | can do this by calling @code{alarm} with a @var{seconds} argument of | |
2770 | zero. | |
2771 | ||
2772 | The return value indicates how many seconds remain before the previous | |
9269924c | 2773 | alarm would have been sent. If there was no previous alarm, @code{alarm} |
28f540f4 RM |
2774 | returns zero. |
2775 | @end deftypefun | |
2776 | ||
2777 | The @code{alarm} function could be defined in terms of @code{setitimer} | |
2778 | like this: | |
2779 | ||
2780 | @smallexample | |
2781 | unsigned int | |
2782 | alarm (unsigned int seconds) | |
2783 | @{ | |
2784 | struct itimerval old, new; | |
2785 | new.it_interval.tv_usec = 0; | |
2786 | new.it_interval.tv_sec = 0; | |
2787 | new.it_value.tv_usec = 0; | |
2788 | new.it_value.tv_sec = (long int) seconds; | |
2789 | if (setitimer (ITIMER_REAL, &new, &old) < 0) | |
2790 | return 0; | |
2791 | else | |
2792 | return old.it_value.tv_sec; | |
2793 | @} | |
2794 | @end smallexample | |
2795 | ||
2796 | There is an example showing the use of the @code{alarm} function in | |
2797 | @ref{Handler Returns}. | |
2798 | ||
2799 | If you simply want your process to wait for a given number of seconds, | |
2800 | you should use the @code{sleep} function. @xref{Sleeping}. | |
2801 | ||
2802 | You shouldn't count on the signal arriving precisely when the timer | |
2803 | expires. In a multiprocessing environment there is typically some | |
2804 | amount of delay involved. | |
2805 | ||
2806 | @strong{Portability Note:} The @code{setitimer} and @code{getitimer} | |
2807 | functions are derived from BSD Unix, while the @code{alarm} function is | |
2808 | specified by the POSIX.1 standard. @code{setitimer} is more powerful than | |
2809 | @code{alarm}, but @code{alarm} is more widely used. | |
2810 | ||
2811 | @node Sleeping | |
2812 | @section Sleeping | |
2813 | ||
2814 | The function @code{sleep} gives a simple way to make the program wait | |
99a20616 UD |
2815 | for a short interval. If your program doesn't use signals (except to |
2816 | terminate), then you can expect @code{sleep} to wait reliably throughout | |
2817 | the specified interval. Otherwise, @code{sleep} can return sooner if a | |
2818 | signal arrives; if you want to wait for a given interval regardless of | |
2819 | signals, use @code{select} (@pxref{Waiting for I/O}) and don't specify | |
2820 | any descriptors to wait for. | |
28f540f4 RM |
2821 | @c !!! select can get EINTR; using SA_RESTART makes sleep win too. |
2822 | ||
28f540f4 | 2823 | @deftypefun {unsigned int} sleep (unsigned int @var{seconds}) |
d08a7e4c | 2824 | @standards{POSIX.1, unistd.h} |
23e5b8cb AO |
2825 | @safety{@prelim{}@mtunsafe{@mtascusig{:SIGCHLD/linux}}@asunsafe{}@acunsafe{}} |
2826 | @c On Mach, it uses ports and calls time. On generic posix, it calls | |
2827 | @c nanosleep. On Linux, it temporarily blocks SIGCHLD, which is MT- and | |
2828 | @c AS-Unsafe, and in a way that makes it AC-Unsafe (C-unsafe, even!). | |
9269924c | 2829 | The @code{sleep} function waits for @var{seconds} seconds or until a signal |
01cdeca0 | 2830 | is delivered, whichever happens first. |
28f540f4 | 2831 | |
9269924c | 2832 | If @code{sleep} returns because the requested interval is over, |
99a20616 UD |
2833 | it returns a value of zero. If it returns because of delivery of a |
2834 | signal, its return value is the remaining time in the sleep interval. | |
28f540f4 RM |
2835 | |
2836 | The @code{sleep} function is declared in @file{unistd.h}. | |
2837 | @end deftypefun | |
2838 | ||
2839 | Resist the temptation to implement a sleep for a fixed amount of time by | |
2840 | using the return value of @code{sleep}, when nonzero, to call | |
2841 | @code{sleep} again. This will work with a certain amount of accuracy as | |
2842 | long as signals arrive infrequently. But each signal can cause the | |
2843 | eventual wakeup time to be off by an additional second or so. Suppose a | |
2844 | few signals happen to arrive in rapid succession by bad luck---there is | |
2845 | no limit on how much this could shorten or lengthen the wait. | |
2846 | ||
99a20616 UD |
2847 | Instead, compute the calendar time at which the program should stop |
2848 | waiting, and keep trying to wait until that calendar time. This won't | |
2849 | be off by more than a second. With just a little more work, you can use | |
2850 | @code{select} and make the waiting period quite accurate. (Of course, | |
2851 | heavy system load can cause additional unavoidable delays---unless the | |
2852 | machine is dedicated to one application, there is no way you can avoid | |
2853 | this.) | |
28f540f4 RM |
2854 | |
2855 | On some systems, @code{sleep} can do strange things if your program uses | |
2856 | @code{SIGALRM} explicitly. Even if @code{SIGALRM} signals are being | |
2857 | ignored or blocked when @code{sleep} is called, @code{sleep} might | |
2858 | return prematurely on delivery of a @code{SIGALRM} signal. If you have | |
2859 | established a handler for @code{SIGALRM} signals and a @code{SIGALRM} | |
2860 | signal is delivered while the process is sleeping, the action taken | |
2861 | might be just to cause @code{sleep} to return instead of invoking your | |
2862 | handler. And, if @code{sleep} is interrupted by delivery of a signal | |
2863 | whose handler requests an alarm or alters the handling of @code{SIGALRM}, | |
2864 | this handler and @code{sleep} will interfere. | |
2865 | ||
a7a93d50 | 2866 | On @gnusystems{}, it is safe to use @code{sleep} and @code{SIGALRM} in |
28f540f4 RM |
2867 | the same program, because @code{sleep} does not work by means of |
2868 | @code{SIGALRM}. | |
2869 | ||
dfd2257a | 2870 | @deftypefun int nanosleep (const struct timespec *@var{requested_time}, struct timespec *@var{remaining}) |
d08a7e4c | 2871 | @standards{POSIX.1, time.h} |
23e5b8cb AO |
2872 | @safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} |
2873 | @c On Linux, it's a syscall. On Mach, it calls gettimeofday and uses | |
2874 | @c ports. | |
99a20616 UD |
2875 | If resolution to seconds is not enough the @code{nanosleep} function can |
2876 | be used. As the name suggests the sleep interval can be specified in | |
2877 | nanoseconds. The actual elapsed time of the sleep interval might be | |
2878 | longer since the system rounds the elapsed time you request up to the | |
2879 | next integer multiple of the actual resolution the system can deliver. | |
dfd2257a | 2880 | |
99a20616 UD |
2881 | *@code{requested_time} is the elapsed time of the interval you want to |
2882 | sleep. | |
2883 | ||
2884 | The function returns as *@code{remaining} the elapsed time left in the | |
2885 | interval for which you requested to sleep. If the interval completed | |
2886 | without getting interrupted by a signal, this is zero. | |
2887 | ||
b642f101 | 2888 | @code{struct timespec} is described in @xref{Elapsed Time}. |
99a20616 UD |
2889 | |
2890 | If the function returns because the interval is over the return value is | |
010fe231 | 2891 | zero. If the function returns @math{-1} the global variable @code{errno} |
dfd2257a UD |
2892 | is set to the following values: |
2893 | ||
2894 | @table @code | |
2895 | @item EINTR | |
2896 | The call was interrupted because a signal was delivered to the thread. | |
2897 | If the @var{remaining} parameter is not the null pointer the structure | |
99a20616 UD |
2898 | pointed to by @var{remaining} is updated to contain the remaining |
2899 | elapsed time. | |
dfd2257a UD |
2900 | |
2901 | @item EINVAL | |
2902 | The nanosecond value in the @var{requested_time} parameter contains an | |
2903 | illegal value. Either the value is negative or greater than or equal to | |
2904 | 1000 million. | |
2905 | @end table | |
2906 | ||
76c23bac | 2907 | This function is a cancellation point in multi-threaded programs. This |
dfd2257a UD |
2908 | is a problem if the thread allocates some resources (like memory, file |
2909 | descriptors, semaphores or whatever) at the time @code{nanosleep} is | |
2910 | called. If the thread gets canceled these resources stay allocated | |
2911 | until the program ends. To avoid this calls to @code{nanosleep} should | |
76c23bac | 2912 | be protected using cancellation handlers. |
dfd2257a UD |
2913 | @c ref pthread_cleanup_push / pthread_cleanup_pop |
2914 | ||
2915 | The @code{nanosleep} function is declared in @file{time.h}. | |
2916 | @end deftypefun |