-@node Date and Time, Non-Local Exits, Arithmetic, Top
+@node Date and Time, Resource Usage And Limitation, Arithmetic, Top
+@c %MENU% Functions for getting the date and time and formatting them nicely
@chapter Date and Time
This chapter describes functions for manipulating dates and times,
-including functions for determining what the current time is and
-conversion between different time representations.
-
-The time functions fall into three main categories:
-
-@itemize @bullet
-@item
-Functions for measuring elapsed CPU time are discussed in @ref{Processor
-Time}.
-
-@item
-Functions for measuring absolute clock or calendar time are discussed in
-@ref{Calendar Time}.
-
-@item
-Functions for setting alarms and timers are discussed in @ref{Setting
-an Alarm}.
-@end itemize
+including functions for determining what time it is and conversion
+between different time representations.
@menu
-* Processor Time:: Measures processor time used by a program.
+* Time Basics:: Concepts and definitions.
+* Elapsed Time:: Data types to represent elapsed times
+* Processor And CPU Time:: Time a program has spent executing.
* Calendar Time:: Manipulation of ``real'' dates and times.
* Setting an Alarm:: Sending a signal after a specified time.
* Sleeping:: Waiting for a period of time.
-* Resource Usage:: Measuring various resources used.
-* Limits on Resources:: Specifying limits on resource usage.
-* Priority:: Reading or setting process run priority.
@end menu
-@node Processor Time
-@section Processor Time
-
-If you're trying to optimize your program or measure its efficiency, it's
-very useful to be able to know how much @dfn{processor time} or @dfn{CPU
-time} it has used at any given point. Processor time is different from
-actual wall clock time because it doesn't include any time spent waiting
-for I/O or when some other process is running. Processor time is
-represented by the data type @code{clock_t}, and is given as a number of
-@dfn{clock ticks} relative to an arbitrary base time marking the beginning
-of a single program invocation.
+
+@node Time Basics
+@section Time Basics
+@cindex time
+
+Discussing time in a technical manual can be difficult because the word
+``time'' in English refers to lots of different things. In this manual,
+we use a rigorous terminology to avoid confusion, and the only thing we
+use the simple word ``time'' for is to talk about the abstract concept.
+
+A @dfn{calendar time} is a point in the time continuum, for example
+November 4, 1990, at 18:02.5 UTC. Sometimes this is called ``absolute
+time''.
+@cindex calendar time
+
+We don't speak of a ``date'', because that is inherent in a calendar
+time.
+@cindex date
+
+An @dfn{interval} is a contiguous part of the time continuum between two
+calendar times, for example the hour between 9:00 and 10:00 on July 4,
+1980.
+@cindex interval
+
+An @dfn{elapsed time} is the length of an interval, for example, 35
+minutes. People sometimes sloppily use the word ``interval'' to refer
+to the elapsed time of some interval.
+@cindex elapsed time
+@cindex time, elapsed
+
+An @dfn{amount of time} is a sum of elapsed times, which need not be of
+any specific intervals. For example, the amount of time it takes to
+read a book might be 9 hours, independently of when and in how many
+sittings it is read.
+
+A @dfn{period} is the elapsed time of an interval between two events,
+especially when they are part of a sequence of regularly repeating
+events.
+@cindex period of time
+
+@dfn{CPU time} is like calendar time, except that it is based on the
+subset of the time continuum when a particular process is actively
+using a CPU. CPU time is, therefore, relative to a process.
@cindex CPU time
+
+@dfn{Processor time} is an amount of time that a CPU is in use. In
+fact, it's a basic system resource, since there's a limit to how much
+can exist in any given interval (that limit is the elapsed time of the
+interval times the number of CPUs in the processor). People often call
+this CPU time, but we reserve the latter term in this manual for the
+definition above.
@cindex processor time
+
+@node Elapsed Time
+@section Elapsed Time
+@cindex elapsed time
+
+One way to represent an elapsed time is with a simple arithmetic data
+type, as with the following function to compute the elapsed time between
+two calendar times. This function is declared in @file{time.h}.
+
+@deftypefun double difftime (time_t @var{time1}, time_t @var{time0})
+@standards{ISO, time.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+The @code{difftime} function returns the number of seconds of elapsed
+time between calendar time @var{time1} and calendar time @var{time0}, as
+a value of type @code{double}. The difference ignores leap seconds
+unless leap second support is enabled.
+
+In @theglibc{}, you can simply subtract @code{time_t} values. But on
+other systems, the @code{time_t} data type might use some other encoding
+where subtraction doesn't work directly.
+@end deftypefun
+
+@Theglibc{} provides two data types specifically for representing
+an elapsed time. They are used by various @glibcadj{} functions, and
+you can use them for your own purposes too. They're exactly the same
+except that one has a resolution in microseconds, and the other, newer
+one, is in nanoseconds.
+
+@deftp {Data Type} {struct timeval}
+@standards{BSD, sys/time.h}
+@cindex timeval
+The @code{struct timeval} structure represents an elapsed time. It is
+declared in @file{sys/time.h} and has the following members:
+
+@table @code
+@item time_t tv_sec
+This represents the number of whole seconds of elapsed time.
+
+@item long int tv_usec
+This is the rest of the elapsed time (a fraction of a second),
+represented as the number of microseconds. It is always less than one
+million.
+
+@end table
+@end deftp
+
+@deftp {Data Type} {struct timespec}
+@standards{POSIX.1, sys/time.h}
+@cindex timespec
+The @code{struct timespec} structure represents an elapsed time. It is
+declared in @file{time.h} and has the following members:
+
+@table @code
+@item time_t tv_sec
+This represents the number of whole seconds of elapsed time.
+
+@item long int tv_nsec
+This is the rest of the elapsed time (a fraction of a second),
+represented as the number of nanoseconds. It is always less than one
+billion.
+
+@end table
+@end deftp
+
+It is often necessary to subtract two values of type @w{@code{struct
+timeval}} or @w{@code{struct timespec}}. Here is the best way to do
+this. It works even on some peculiar operating systems where the
+@code{tv_sec} member has an unsigned type.
+
+@smallexample
+@include timeval_subtract.c.texi
+@end smallexample
+
+Common functions that use @code{struct timeval} are @code{gettimeofday}
+and @code{settimeofday}.
+
+
+There are no @glibcadj{} functions specifically oriented toward
+dealing with elapsed times, but the calendar time, processor time, and
+alarm and sleeping functions have a lot to do with them.
+
+
+@node Processor And CPU Time
+@section Processor And CPU Time
+
+If you're trying to optimize your program or measure its efficiency,
+it's very useful to know how much processor time it uses. For that,
+calendar time and elapsed times are useless because a process may spend
+time waiting for I/O or for other processes to use the CPU. However,
+you can get the information with the functions in this section.
+
+CPU time (@pxref{Time Basics}) is represented by the data type
+@code{clock_t}, which is a number of @dfn{clock ticks}. It gives the
+total amount of time a process has actively used a CPU since some
+arbitrary event. On @gnusystems{}, that event is the creation of the
+process. While arbitrary in general, the event is always the same event
+for any particular process, so you can always measure how much time on
+the CPU a particular computation takes by examining the process' CPU
+time before and after the computation.
+@cindex CPU time
@cindex clock ticks
@cindex ticks, clock
-@cindex time, elapsed CPU
+
+On @gnulinuxhurdsystems{}, @code{clock_t} is equivalent to @code{long int} and
+@code{CLOCKS_PER_SEC} is an integer value. But in other systems, both
+@code{clock_t} and the macro @code{CLOCKS_PER_SEC} can be either integer
+or floating-point types. Casting CPU time values to @code{double}, as
+in the example above, makes sure that operations such as arithmetic and
+printing work properly and consistently no matter what the underlying
+representation is.
+
+Note that the clock can wrap around. On a 32bit system with
+@code{CLOCKS_PER_SEC} set to one million this function will return the
+same value approximately every 72 minutes.
+
+For additional functions to examine a process' use of processor time,
+and to control it, see @ref{Resource Usage And Limitation}.
+
@menu
-* Basic CPU Time:: The @code{clock} function.
-* Detailed CPU Time:: The @code{times} function.
+* CPU Time:: The @code{clock} function.
+* Processor Time:: The @code{times} function.
@end menu
-@node Basic CPU Time
-@subsection Basic CPU Time Inquiry
+@node CPU Time
+@subsection CPU Time Inquiry
-To get the elapsed CPU time used by a process, you can use the
-@code{clock} function. This facility is declared in the header file
-@file{time.h}.
+To get a process' CPU time, you can use the @code{clock} function. This
+facility is declared in the header file @file{time.h}.
@pindex time.h
-In typical usage, you call the @code{clock} function at the beginning and
-end of the interval you want to time, subtract the values, and then divide
-by @code{CLOCKS_PER_SEC} (the number of clock ticks per second), like this:
+In typical usage, you call the @code{clock} function at the beginning
+and end of the interval you want to time, subtract the values, and then
+divide by @code{CLOCKS_PER_SEC} (the number of clock ticks per second)
+to get processor time, like this:
@smallexample
@group
#include <time.h>
clock_t start, end;
-double elapsed;
+double cpu_time_used;
start = clock();
@dots{} /* @r{Do the work.} */
end = clock();
-elapsed = ((double) (end - start)) / CLOCKS_PER_SEC;
+cpu_time_used = ((double) (end - start)) / CLOCKS_PER_SEC;
@end group
@end smallexample
+Do not use a single CPU time as an amount of time; it doesn't work that
+way. Either do a subtraction as shown above or query processor time
+directly. @xref{Processor Time}.
+
Different computers and operating systems vary wildly in how they keep
-track of processor time. It's common for the internal processor clock
-to have a resolution somewhere between hundredths and millionths of a
+track of CPU time. It's common for the internal processor clock
+to have a resolution somewhere between a hundredth and millionth of a
second.
-In the GNU system, @code{clock_t} is equivalent to @code{long int} and
-@code{CLOCKS_PER_SEC} is an integer value. But in other systems, both
-@code{clock_t} and the type of the macro @code{CLOCKS_PER_SEC} can be
-either integer or floating-point types. Casting processor time values
-to @code{double}, as in the example above, makes sure that operations
-such as arithmetic and printing work properly and consistently no matter
-what the underlying representation is.
-
-@comment time.h
-@comment ANSI
@deftypevr Macro int CLOCKS_PER_SEC
+@standards{ISO, time.h}
The value of this macro is the number of clock ticks per second measured
-by the @code{clock} function.
+by the @code{clock} function. POSIX requires that this value be one
+million independent of the actual resolution.
@end deftypevr
-@comment time.h
-@comment POSIX.1
-@deftypevr Macro int CLK_TCK
-This is an obsolete name for @code{CLOCKS_PER_SEC}.
-@end deftypevr
-
-@comment time.h
-@comment ANSI
@deftp {Data Type} clock_t
+@standards{ISO, time.h}
This is the type of the value returned by the @code{clock} function.
-Values of type @code{clock_t} are in units of clock ticks.
+Values of type @code{clock_t} are numbers of clock ticks.
@end deftp
-@comment time.h
-@comment ANSI
@deftypefun clock_t clock (void)
-This function returns the elapsed processor time. The base time is
-arbitrary but doesn't change within a single process. If the processor
+@standards{ISO, time.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+@c On Hurd, this calls task_info twice and adds user and system time
+@c from both basic and thread time info structs. On generic posix,
+@c calls times and adds utime and stime. On bsd, calls getrusage and
+@c safely converts stime and utime to clock. On linux, calls
+@c clock_gettime.
+This function returns the calling process' current CPU time. If the CPU
time is not available or cannot be represented, @code{clock} returns the
value @code{(clock_t)(-1)}.
@end deftypefun
-@node Detailed CPU Time
-@subsection Detailed Elapsed CPU Time Inquiry
+@node Processor Time
+@subsection Processor Time Inquiry
-The @code{times} function returns more detailed information about
-elapsed processor time in a @w{@code{struct tms}} object. You should
+The @code{times} function returns information about a process'
+consumption of processor time in a @w{@code{struct tms}} object, in
+addition to the process' CPU time. @xref{Time Basics}. You should
include the header file @file{sys/times.h} to use this facility.
+@cindex processor time
+@cindex CPU time
@pindex sys/times.h
-@comment sys/times.h
-@comment POSIX.1
@deftp {Data Type} {struct tms}
+@standards{POSIX.1, sys/times.h}
The @code{tms} structure is used to return information about process
times. It contains at least the following members:
@table @code
@item clock_t tms_utime
-This is the CPU time used in executing the instructions of the calling
-process.
+This is the total processor time the calling process has used in
+executing the instructions of its program.
@item clock_t tms_stime
-This is the CPU time used by the system on behalf of the calling process.
+This is the processor time the system has used on behalf of the calling
+process.
@item clock_t tms_cutime
This is the sum of the @code{tms_utime} values and the @code{tms_cutime}
values of all terminated child processes of the calling process, whose
status has been reported to the parent process by @code{wait} or
@code{waitpid}; see @ref{Process Completion}. In other words, it
-represents the total CPU time used in executing the instructions of all
-the terminated child processes of the calling process, excluding child
-processes which have not yet been reported by @code{wait} or
+represents the total processor time used in executing the instructions
+of all the terminated child processes of the calling process, excluding
+child processes which have not yet been reported by @code{wait} or
@code{waitpid}.
+@cindex child process
@item clock_t tms_cstime
-This is similar to @code{tms_cutime}, but represents the total CPU time
-used by the system on behalf of all the terminated child processes of the
-calling process.
+This is similar to @code{tms_cutime}, but represents the total processor
+time the system has used on behalf of all the terminated child processes
+of the calling process.
@end table
-All of the times are given in clock ticks. These are absolute values; in a
-newly created process, they are all zero. @xref{Creating a Process}.
+All of the times are given in numbers of clock ticks. Unlike CPU time,
+these are the actual amounts of time; not relative to any event.
+@xref{Creating a Process}.
@end deftp
-@comment sys/times.h
-@comment POSIX.1
+@deftypevr Macro int CLK_TCK
+@standards{POSIX.1, time.h}
+This is an obsolete name for the number of clock ticks per second. Use
+@code{sysconf (_SC_CLK_TCK)} instead.
+@end deftypevr
+
@deftypefun clock_t times (struct tms *@var{buffer})
+@standards{POSIX.1, sys/times.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+@c On HURD, this calls task_info twice, for basic and thread times info,
+@c adding user and system times into tms, and then gettimeofday, to
+@c compute the real time. On BSD, it calls getclktck, getrusage (twice)
+@c and time. On Linux, it's a syscall with special handling to account
+@c for clock_t counts that look like error values.
The @code{times} function stores the processor time information for
the calling process in @var{buffer}.
-The return value is the same as the value of @code{clock()}: the elapsed
-real time relative to an arbitrary base. The base is a constant within a
-particular process, and typically represents the time since system
-start-up. A value of @code{(clock_t)(-1)} is returned to indicate failure.
+The return value is the number of clock ticks since an arbitrary point
+in the past, e.g. since system start-up. @code{times} returns
+@code{(clock_t)(-1)} to indicate failure.
@end deftypefun
@strong{Portability Note:} The @code{clock} function described in
-@ref{Basic CPU Time}, is specified by the ANSI C standard. The
-@code{times} function is a feature of POSIX.1. In the GNU system, the
-value returned by the @code{clock} function is equivalent to the sum of
-the @code{tms_utime} and @code{tms_stime} fields returned by
-@code{times}.
+@ref{CPU Time} is specified by the @w{ISO C} standard. The
+@code{times} function is a feature of POSIX.1. On @gnusystems{}, the
+CPU time is defined to be equivalent to the sum of the @code{tms_utime}
+and @code{tms_stime} fields returned by @code{times}.
@node Calendar Time
@section Calendar Time
-This section describes facilities for keeping track of dates and times
-according to the Gregorian calendar.
-@cindex Gregorian calendar
-@cindex time, calendar
-@cindex date and time
+This section describes facilities for keeping track of calendar time.
+@xref{Time Basics}.
-There are three representations for date and time information:
+@Theglibc{} represents calendar time three ways:
@itemize @bullet
-@item
-@dfn{Calendar time} (the @code{time_t} data type) is a compact
-representation, typically giving the number of seconds elapsed since
-some implementation-specific base time.
-@cindex calendar time
+@item
+@dfn{Simple time} (the @code{time_t} data type) is a compact
+representation, typically giving the number of seconds of elapsed time
+since some implementation-specific base time.
+@cindex simple time
@item
-There is also a @dfn{high-resolution time} representation (the @code{struct
-timeval} data type) that includes fractions of a second. Use this time
-representation instead of ordinary calendar time when you need greater
-precision.
+There is also a "high-resolution time" representation. Like simple
+time, this represents a calendar time as an elapsed time since a base
+time, but instead of measuring in whole seconds, it uses a @code{struct
+timeval} data type, which includes fractions of a second. Use this time
+representation instead of simple time when you need greater precision.
@cindex high-resolution time
@item
-@dfn{Local time} or @dfn{broken-down time} (the @code{struct
-tm} data type) represents the date and time as a set of components
-specifying the year, month, and so on, for a specific time zone.
-This time representation is usually used in conjunction with formatting
-date and time values.
+@dfn{Local time} or @dfn{broken-down time} (the @code{struct tm} data
+type) represents a calendar time as a set of components specifying the
+year, month, and so on in the Gregorian calendar, for a specific time
+zone. This calendar time representation is usually used only to
+communicate with people.
@cindex local time
@cindex broken-down time
+@cindex Gregorian calendar
+@cindex calendar, Gregorian
@end itemize
@menu
* Simple Calendar Time:: Facilities for manipulating calendar time.
* High-Resolution Calendar:: A time representation with greater precision.
* Broken-down Time:: Facilities for manipulating local time.
-* Formatting Date and Time:: Converting times to strings.
+* High Accuracy Clock:: Maintaining a high accuracy system clock.
+* Formatting Calendar Time:: Converting times to strings.
+* Parsing Date and Time:: Convert textual time and date information back
+ into broken-down time values.
* TZ Variable:: How users specify the time zone.
-* Time Zone Functions:: Functions to examine or specify the time zone.
+* Time Zone Functions:: Functions to examine or specify the time zone.
* Time Functions Example:: An example program showing use of some of
the time functions.
@end menu
@node Simple Calendar Time
@subsection Simple Calendar Time
-This section describes the @code{time_t} data type for representing
-calendar time, and the functions which operate on calendar time objects.
+This section describes the @code{time_t} data type for representing calendar
+time as simple time, and the functions which operate on simple time objects.
These facilities are declared in the header file @file{time.h}.
@pindex time.h
@cindex epoch
-@comment time.h
-@comment ANSI
@deftp {Data Type} time_t
-This is the data type used to represent calendar time.
-When interpreted as an absolute time
-value, it represents the number of seconds elapsed since 00:00:00 on
-January 1, 1970, Coordinated Universal Time. (This date is sometimes
-referred to as the @dfn{epoch}.) POSIX requires that this count
-ignore leap seconds, but on some hosts this count includes leap seconds
+@standards{ISO, time.h}
+This is the data type used to represent simple time. Sometimes, it also
+represents an elapsed time. When interpreted as a calendar time value,
+it represents the number of seconds elapsed since 00:00:00 on January 1,
+1970, Coordinated Universal Time. (This calendar time is sometimes
+referred to as the @dfn{epoch}.) POSIX requires that this count not
+include leap seconds, but on some systems this count includes leap seconds
if you set @code{TZ} to certain values (@pxref{TZ Variable}).
-In the GNU C library, @code{time_t} is equivalent to @code{long int}.
+Note that a simple time has no concept of local time zone. Calendar
+Time @var{T} is the same instant in time regardless of where on the
+globe the computer is.
+
+In @theglibc{}, @code{time_t} is equivalent to @code{long int}.
In other systems, @code{time_t} might be either an integer or
floating-point type.
@end deftp
-@comment time.h
-@comment ANSI
-@deftypefun double difftime (time_t @var{time1}, time_t @var{time0})
-The @code{difftime} function returns the number of seconds elapsed
-between time @var{time1} and time @var{time0}, as a value of type
-@code{double}. The difference ignores leap seconds unless leap
-second support is enabled.
+The function @code{difftime} tells you the elapsed time between two
+simple calendar times, which is not always as easy to compute as just
+subtracting. @xref{Elapsed Time}.
-In the GNU system, you can simply subtract @code{time_t} values. But on
-other systems, the @code{time_t} data type might use some other encoding
-where subtraction doesn't work directly.
+@deftypefun time_t time (time_t *@var{result})
+@standards{ISO, time.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+The @code{time} function returns the current calendar time as a value of
+type @code{time_t}. If the argument @var{result} is not a null pointer,
+the calendar time value is also stored in @code{*@var{result}}. If the
+current calendar time is not available, the value
+@w{@code{(time_t)(-1)}} is returned.
@end deftypefun
-@comment time.h
-@comment ANSI
-@deftypefun time_t time (time_t *@var{result})
-The @code{time} function returns the current time as a value of type
-@code{time_t}. If the argument @var{result} is not a null pointer, the
-time value is also stored in @code{*@var{result}}. If the calendar
-time is not available, the value @w{@code{(time_t)(-1)}} is returned.
+@c The GNU C library implements stime() with a call to settimeofday() on
+@c Linux.
+@deftypefun int stime (const time_t *@var{newtime})
+@standards{SVID, time.h}
+@standards{XPG, time.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+@c On unix, this is implemented in terms of settimeofday.
+@code{stime} sets the system clock, i.e., it tells the system that the
+current calendar time is @var{newtime}, where @code{newtime} is
+interpreted as described in the above definition of @code{time_t}.
+
+@code{settimeofday} is a newer function which sets the system clock to
+better than one second precision. @code{settimeofday} is generally a
+better choice than @code{stime}. @xref{High-Resolution Calendar}.
+
+Only the superuser can set the system clock.
+
+If the function succeeds, the return value is zero. Otherwise, it is
+@code{-1} and @code{errno} is set accordingly:
+
+@table @code
+@item EPERM
+The process is not superuser.
+@end table
@end deftypefun
+
@node High-Resolution Calendar
@subsection High-Resolution Calendar
-The @code{time_t} data type used to represent calendar times has a
+The @code{time_t} data type used to represent simple times has a
resolution of only one second. Some applications need more precision.
-So, the GNU C library also contains functions which are capable of
+So, @theglibc{} also contains functions which are capable of
representing calendar times to a higher resolution than one second. The
functions and the associated data types described in this section are
declared in @file{sys/time.h}.
@pindex sys/time.h
-@comment sys/time.h
-@comment BSD
-@deftp {Data Type} {struct timeval}
-The @code{struct timeval} structure represents a calendar time. It
-has the following members:
-
-@table @code
-@item long int tv_sec
-This represents the number of seconds since the epoch. It is equivalent
-to a normal @code{time_t} value.
-
-@item long int tv_usec
-This is the fractional second value, represented as the number of
-microseconds.
-
-Some times struct timeval values are used for time intervals. Then the
-@code{tv_sec} member is the number of seconds in the interval, and
-@code{tv_usec} is the number of additional microseconds.
-@end table
-@end deftp
-
-@comment sys/time.h
-@comment BSD
@deftp {Data Type} {struct timezone}
+@standards{BSD, sys/time.h}
The @code{struct timezone} structure is used to hold minimal information
about the local time zone. It has the following members:
@table @code
@item int tz_minuteswest
-This is the number of minutes west of GMT.
+This is the number of minutes west of UTC.
@item int tz_dsttime
-If nonzero, daylight savings time applies during some part of the year.
+If nonzero, Daylight Saving Time applies during some part of the year.
@end table
The @code{struct timezone} type is obsolete and should never be used.
Instead, use the facilities described in @ref{Time Zone Functions}.
@end deftp
-It is often necessary to subtract two values of type @w{@code{struct
-timeval}}. Here is the best way to do this. It works even on some
-peculiar operating systems where the @code{tv_sec} member has an
-unsigned type.
-
-@smallexample
-/* @r{Subtract the `struct timeval' values X and Y,}
- @r{storing the result in RESULT.}
- @r{Return 1 if the difference is negative, otherwise 0.} */
-
-int
-timeval_subtract (result, x, y)
- struct timeval *result, *x, *y;
-@{
- /* @r{Perform the carry for the later subtraction by updating @var{y}.} */
- if (x->tv_usec < y->tv_usec) @{
- int nsec = (y->tv_usec - x->tv_usec) / 1000000 + 1;
- y->tv_usec -= 1000000 * nsec;
- y->tv_sec += nsec;
- @}
- if (x->tv_usec - y->tv_usec > 1000000) @{
- int nsec = (y->tv_usec - x->tv_usec) / 1000000;
- y->tv_usec += 1000000 * nsec;
- y->tv_sec -= nsec;
- @}
-
- /* @r{Compute the time remaining to wait.}
- @r{@code{tv_usec} is certainly positive.} */
- result->tv_sec = x->tv_sec - y->tv_sec;
- result->tv_usec = x->tv_usec - y->tv_usec;
-
- /* @r{Return 1 if result is negative.} */
- return x->tv_sec < y->tv_sec;
-@}
-@end smallexample
-
-@comment sys/time.h
-@comment BSD
@deftypefun int gettimeofday (struct timeval *@var{tp}, struct timezone *@var{tzp})
-The @code{gettimeofday} function returns the current date and time in the
-@code{struct timeval} structure indicated by @var{tp}. Information about the
-time zone is returned in the structure pointed at @var{tzp}. If the @var{tzp}
-argument is a null pointer, time zone information is ignored.
+@standards{BSD, sys/time.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+@c On most GNU/Linux systems this is a direct syscall, but the posix/
+@c implementation (not used on GNU/Linux or GNU/Hurd) relies on time and
+@c localtime_r, saving and restoring tzname in an unsafe manner.
+@c On some GNU/Linux variants, ifunc resolvers are used in shared libc
+@c for vdso resolution. ifunc-vdso-revisit.
+The @code{gettimeofday} function returns the current calendar time as
+the elapsed time since the epoch in the @code{struct timeval} structure
+indicated by @var{tp}. (@pxref{Elapsed Time} for a description of
+@code{struct timeval}). Information about the time zone is returned in
+the structure pointed to by @var{tzp}. If the @var{tzp} argument is a null
+pointer, time zone information is ignored.
The return value is @code{0} on success and @code{-1} on failure. The
following @code{errno} error condition is defined for this function:
@table @code
@item ENOSYS
The operating system does not support getting time zone information, and
-@var{tzp} is not a null pointer. The GNU operating system does not
+@var{tzp} is not a null pointer. @gnusystems{} do not
support using @w{@code{struct timezone}} to represent time zone
information; that is an obsolete feature of 4.3 BSD.
Instead, use the facilities described in @ref{Time Zone Functions}.
@end table
@end deftypefun
-@comment sys/time.h
-@comment BSD
@deftypefun int settimeofday (const struct timeval *@var{tp}, const struct timezone *@var{tzp})
-The @code{settimeofday} function sets the current date and time
-according to the arguments. As for @code{gettimeofday}, time zone
-information is ignored if @var{tzp} is a null pointer.
+@standards{BSD, sys/time.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+@c On HURD, it calls host_set_time with a privileged port. On other
+@c unix systems, it's a syscall.
+The @code{settimeofday} function sets the current calendar time in the
+system clock according to the arguments. As for @code{gettimeofday},
+the calendar time is represented as the elapsed time since the epoch.
+As for @code{gettimeofday}, time zone information is ignored if
+@var{tzp} is a null pointer.
You must be a privileged user in order to use @code{settimeofday}.
+Some kernels automatically set the system clock from some source such as
+a hardware clock when they start up. Others, including Linux, place the
+system clock in an ``invalid'' state (in which attempts to read the clock
+fail). A call of @code{stime} removes the system clock from an invalid
+state, and system startup scripts typically run a program that calls
+@code{stime}.
+
+@code{settimeofday} causes a sudden jump forwards or backwards, which
+can cause a variety of problems in a system. Use @code{adjtime} (below)
+to make a smooth transition from one time to another by temporarily
+speeding up or slowing down the clock.
+
+With a Linux kernel, @code{adjtimex} does the same thing and can also
+make permanent changes to the speed of the system clock so it doesn't
+need to be corrected as often.
+
The return value is @code{0} on success and @code{-1} on failure. The
following @code{errno} error conditions are defined for this function:
@table @code
@item EPERM
-This process cannot set the time because it is not privileged.
+This process cannot set the clock because it is not privileged.
@item ENOSYS
The operating system does not support setting time zone information, and
@end table
@end deftypefun
-@comment sys/time.h
-@comment BSD
+@c On Linux, GNU libc implements adjtime() as a call to adjtimex().
@deftypefun int adjtime (const struct timeval *@var{delta}, struct timeval *@var{olddelta})
+@standards{BSD, sys/time.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+@c On hurd and mach, call host_adjust_time with a privileged port. On
+@c Linux, it's implemented in terms of adjtimex. On other unixen, it's
+@c a syscall.
This function speeds up or slows down the system clock in order to make
-gradual adjustments in the current time. This ensures that the time
-reported by the system clock is always monotonically increasing, which
-might not happen if you simply set the current time.
+a gradual adjustment. This ensures that the calendar time reported by
+the system clock is always monotonically increasing, which might not
+happen if you simply set the clock.
The @var{delta} argument specifies a relative adjustment to be made to
-the current time. If negative, the system clock is slowed down for a
-while until it has lost this much time. If positive, the system clock
-is speeded up for a while.
+the clock time. If negative, the system clock is slowed down for a
+while until it has lost this much elapsed time. If positive, the system
+clock is speeded up for a while.
If the @var{olddelta} argument is not a null pointer, the @code{adjtime}
function returns information about any previous time adjustment that
This function is typically used to synchronize the clocks of computers
in a local network. You must be a privileged user to use it.
+
+With a Linux kernel, you can use the @code{adjtimex} function to
+permanently change the clock speed.
+
The return value is @code{0} on success and @code{-1} on failure. The
following @code{errno} error condition is defined for this function:
@end deftypefun
@strong{Portability Note:} The @code{gettimeofday}, @code{settimeofday},
-and @code{adjtime} functions are derived from BSD.
+and @code{adjtime} functions are derived from BSD.
+
+
+Symbols for the following function are declared in @file{sys/timex.h}.
+@deftypefun int adjtimex (struct timex *@var{timex})
+@standards{GNU, sys/timex.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+@c It's a syscall, only available on linux.
+
+@code{adjtimex} is functionally identical to @code{ntp_adjtime}.
+@xref{High Accuracy Clock}.
+
+This function is present only with a Linux kernel.
+
+@end deftypefun
@node Broken-down Time
@subsection Broken-down Time
@cindex broken-down time
@cindex calendar time and broken-down time
-Calendar time is represented as a number of seconds. This is convenient
-for calculation, but has no resemblance to the way people normally
-represent dates and times. By contrast, @dfn{broken-down time} is a binary
-representation separated into year, month, day, and so on. Broken down
-time values are not useful for calculations, but they are useful for
-printing human readable time.
+Calendar time is represented by the usual @glibcadj{} functions as an
+elapsed time since a fixed base calendar time. This is convenient for
+computation, but has no relation to the way people normally think of
+calendar time. By contrast, @dfn{broken-down time} is a binary
+representation of calendar time separated into year, month, day, and so
+on. Broken-down time values are not useful for calculations, but they
+are useful for printing human readable time information.
-A broken-down time value is always relative to a choice of local time
-zone, and it also indicates which time zone was used.
+A broken-down time value is always relative to a choice of time
+zone, and it also indicates which time zone that is.
The symbols in this section are declared in the header file @file{time.h}.
-@comment time.h
-@comment ANSI
@deftp {Data Type} {struct tm}
+@standards{ISO, time.h}
This is the data type used to represent a broken-down time. The structure
-contains at least the following members, which can appear in any order:
+contains at least the following members, which can appear in any order.
@table @code
@item int tm_sec
-This is the number of seconds after the minute, normally in the range
-@code{0} to @code{59}. (The actual upper limit is @code{60}, to allow
-for leap seconds if leap second support is available.)
+This is the number of full seconds since the top of the minute (normally
+in the range @code{0} through @code{59}, but the actual upper limit is
+@code{60}, to allow for leap seconds if leap second support is
+available).
@cindex leap second
@item int tm_min
-This is the number of minutes after the hour, in the range @code{0} to
-@code{59}.
+This is the number of full minutes since the top of the hour (in the
+range @code{0} through @code{59}).
@item int tm_hour
-This is the number of hours past midnight, in the range @code{0} to
-@code{23}.
+This is the number of full hours past midnight (in the range @code{0} through
+@code{23}).
@item int tm_mday
-This is the day of the month, in the range @code{1} to @code{31}.
+This is the ordinal day of the month (in the range @code{1} through @code{31}).
+Watch out for this one! As the only ordinal number in the structure, it is
+inconsistent with the rest of the structure.
@item int tm_mon
-This is the number of months since January, in the range @code{0} to
-@code{11}.
+This is the number of full calendar months since the beginning of the
+year (in the range @code{0} through @code{11}). Watch out for this one!
+People usually use ordinal numbers for month-of-year (where January = 1).
@item int tm_year
-This is the number of years since @code{1900}.
+This is the number of full calendar years since 1900.
@item int tm_wday
-This is the number of days since Sunday, in the range @code{0} to @code{6}.
+This is the number of full days since Sunday (in the range @code{0} through
+@code{6}).
@item int tm_yday
-This is the number of days since January 1, in the range @code{0} to
-@code{365}.
+This is the number of full days since the beginning of the year (in the
+range @code{0} through @code{365}).
@item int tm_isdst
@cindex Daylight Saving Time
@item long int tm_gmtoff
This field describes the time zone that was used to compute this
-broken-down time value; it is the amount you must add to the local time
-in that zone to get GMT, in units of seconds. The value is like that of
-the variable @code{timezone} (@pxref{Time Zone Functions}). You can
-also think of this as the ``number of seconds west'' of GMT. The
-@code{tm_gmtoff} field is a GNU library extension.
+broken-down time value, including any adjustment for daylight saving; it
+is the number of seconds that you must add to UTC to get local time.
+You can also think of this as the number of seconds east of UTC. For
+example, for U.S. Eastern Standard Time, the value is @code{-5*60*60}.
+The @code{tm_gmtoff} field is derived from BSD and is a GNU library
+extension; it is not visible in a strict @w{ISO C} environment.
@item const char *tm_zone
-This field is the name for the time zone that was used to
-compute this broken-down time value. It is a GNU library extension.
+This field is the name for the time zone that was used to compute this
+broken-down time value. Like @code{tm_gmtoff}, this field is a BSD and
+GNU extension, and is not visible in a strict @w{ISO C} environment.
@end table
@end deftp
-@comment time.h
-@comment ANSI
+
@deftypefun {struct tm *} localtime (const time_t *@var{time})
-The @code{localtime} function converts the calendar time pointed to by
+@standards{ISO, time.h}
+@safety{@prelim{}@mtunsafe{@mtasurace{:tmbuf} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c Calls tz_convert with a static buffer.
+@c localtime @mtasurace:tmbuf @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c tz_convert dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+The @code{localtime} function converts the simple time pointed to by
@var{time} to broken-down time representation, expressed relative to the
user's specified time zone.
or @code{localtime}. (But no other library function overwrites the contents
of this object.)
-Calling @code{localtime} has one other effect: it sets the variable
-@code{tzname} with information about the current time zone. @xref{Time
-Zone Functions}.
+The return value is the null pointer if @var{time} cannot be represented
+as a broken-down time; typically this is because the year cannot fit into
+an @code{int}.
+
+Calling @code{localtime} also sets the current time zone as if
+@code{tzset} were called. @xref{Time Zone Functions}.
@end deftypefun
-@comment time.h
-@comment ANSI
+Using the @code{localtime} function is a big problem in multi-threaded
+programs. The result is returned in a static buffer and this is used in
+all threads. POSIX.1c introduced a variant of this function.
+
+@deftypefun {struct tm *} localtime_r (const time_t *@var{time}, struct tm *@var{resultp})
+@standards{POSIX.1c, time.h}
+@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c localtime_r @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c tz_convert(use_localtime) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c libc_lock_lock dup @asulock @aculock
+@c tzset_internal @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c always called with tzset_lock held
+@c sets static is_initialized before initialization;
+@c reads and sets old_tz; sets tz_rules.
+@c some of the issues only apply on the first call.
+@c subsequent calls only trigger these when called by localtime;
+@c otherwise, they're ok.
+@c getenv dup @mtsenv
+@c strcmp dup ok
+@c strdup @ascuheap
+@c tzfile_read @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c memcmp dup ok
+@c strstr dup ok
+@c getenv dup @mtsenv
+@c asprintf dup @mtslocale @ascuheap @acsmem
+@c stat64 dup ok
+@c fopen dup @ascuheap @asulock @acsmem @acsfd @aculock
+@c fileno dup ok
+@c fstat64 dup ok
+@c fclose dup @ascuheap @asulock @aculock @acsmem @acsfd
+@c free dup @ascuheap @acsmem
+@c fsetlocking dup ok [no @mtasurace:stream @asulock, exclusive]
+@c fread_unlocked dup ok [no @mtasurace:stream @asucorrupt @acucorrupt]
+@c memcpy dup ok
+@c decode ok
+@c bswap_32 dup ok
+@c fseek dup ok [no @mtasurace:stream @asucorrupt @acucorrupt]
+@c ftello dup ok [no @mtasurace:stream @asucorrupt @acucorrupt]
+@c malloc dup @ascuheap @acsmem
+@c decode64 ok
+@c bswap_64 dup ok
+@c getc_unlocked ok [no @mtasurace:stream @asucorrupt @acucorrupt]
+@c tzstring dup @ascuheap @acsmem
+@c compute_tzname_max dup ok [guarded by tzset_lock]
+@c memset dup ok
+@c update_vars ok [guarded by tzset_lock]
+@c sets daylight, timezone, tzname and tzname_cur_max;
+@c called only with tzset_lock held, unless tzset_parse_tz
+@c (internal, but not static) gets called by users; given the its
+@c double-underscore-prefixed name, this interface violation could
+@c be regarded as undefined behavior.
+@c strlen ok
+@c tzset_parse_tz @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c sscanf dup @mtslocale @ascuheap @acsmem
+@c isalnum dup @mtsenv
+@c tzstring @ascuheap @acsmem
+@c reads and changes tzstring_list without synchronization, but
+@c only called with tzset_lock held (save for interface violations)
+@c strlen dup ok
+@c malloc dup @ascuheap @acsmem
+@c strcpy dup ok
+@c isdigit dup @mtslocale
+@c compute_offset ok
+@c tzfile_default @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c sets tzname, timezone, types, zone_names, rule_*off, etc; no guards
+@c strlen dup ok
+@c tzfile_read dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c mempcpy dup ok
+@c compute_tzname_max ok [if guarded by tzset_lock]
+@c iterates over zone_names; no guards
+@c free dup @ascuheap @acsmem
+@c strtoul dup @mtslocale
+@c update_vars dup ok
+@c tzfile_compute(use_localtime) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c sets tzname; no guards. with !use_localtime, as in gmtime, it's ok
+@c tzstring dup @acsuheap @acsmem
+@c tzset_parse_tz dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c offtime dup ok
+@c tz_compute dup ok
+@c strcmp dup ok
+@c offtime ok
+@c isleap dup ok
+@c tz_compute ok
+@c compute_change ok
+@c isleap ok
+@c libc_lock_unlock dup @aculock
+
+The @code{localtime_r} function works just like the @code{localtime}
+function. It takes a pointer to a variable containing a simple time
+and converts it to the broken-down time format.
+
+But the result is not placed in a static buffer. Instead it is placed
+in the object of type @code{struct tm} to which the parameter
+@var{resultp} points.
+
+If the conversion is successful the function returns a pointer to the
+object the result was written into, i.e., it returns @var{resultp}.
+@end deftypefun
+
+
@deftypefun {struct tm *} gmtime (const time_t *@var{time})
+@standards{ISO, time.h}
+@safety{@prelim{}@mtunsafe{@mtasurace{:tmbuf} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c gmtime @mtasurace:tmbuf @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c tz_convert dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
This function is similar to @code{localtime}, except that the broken-down
-time is expressed as Coordinated Universal Time (UTC)---that is, as
-Greenwich Mean Time (GMT) rather than relative to the local time zone.
+time is expressed as Coordinated Universal Time (UTC) (formerly called
+Greenwich Mean Time (GMT)) rather than relative to a local time zone.
-Recall that calendar times are @emph{always} expressed in coordinated
-universal time.
@end deftypefun
-@comment time.h
-@comment ANSI
+As for the @code{localtime} function we have the problem that the result
+is placed in a static variable. POSIX.1c also provides a replacement for
+@code{gmtime}.
+
+@deftypefun {struct tm *} gmtime_r (const time_t *@var{time}, struct tm *@var{resultp})
+@standards{POSIX.1c, time.h}
+@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c You'd think tz_convert could avoid some safety issues with
+@c !use_localtime, but no such luck: tzset_internal will always bring
+@c about all possible AS and AC problems when it's first called.
+@c Calling any of localtime,gmtime_r once would run the initialization
+@c and avoid the heap, mem and fd issues in gmtime* in subsequent calls,
+@c but the unsafe locking would remain.
+@c gmtime_r @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c tz_convert(gmtime_r) dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+This function is similar to @code{localtime_r}, except that it converts
+just like @code{gmtime} the given time as Coordinated Universal Time.
+
+If the conversion is successful the function returns a pointer to the
+object the result was written into, i.e., it returns @var{resultp}.
+@end deftypefun
+
+
@deftypefun time_t mktime (struct tm *@var{brokentime})
-The @code{mktime} function is used to convert a broken-down time structure
-to a calendar time representation. It also ``normalizes'' the contents of
-the broken-down time structure, by filling in the day of week and day of
-year based on the other date and time components.
+@standards{ISO, time.h}
+@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c mktime @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c passes a static localtime_offset to mktime_internal; it is read
+@c once, used as an initial guess, and updated at the end, but not
+@c used except as a guess for subsequent calls, so it should be safe.
+@c Even though a compiler might delay the load and perform it multiple
+@c times (bug 16346), there are at least two unconditional uses of the
+@c auto variable in which the first load is stored, separated by a
+@c call to an external function, and a conditional change of the
+@c variable before the external call, so refraining from allocating a
+@c local variable at the first load would be a very bad optimization.
+@c tzset dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c mktime_internal(localtime_r) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c ydhms_diff ok
+@c ranged_convert(localtime_r) @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c *convert = localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c time_t_avg dup ok
+@c guess_time_tm dup ok
+@c ydhms_diff dup ok
+@c time_t_add_ok ok
+@c time_t_avg ok
+@c isdst_differ ok
+@c time_t_int_add_ok ok
+The @code{mktime} function converts a broken-down time structure to a
+simple time representation. It also normalizes the contents of the
+broken-down time structure, and fills in some components based on the
+values of the others.
The @code{mktime} function ignores the specified contents of the
-@code{tm_wday} and @code{tm_yday} members of the broken-down time
-structure. It uses the values of the other components to compute the
+@code{tm_wday}, @code{tm_yday}, @code{tm_gmtoff}, and @code{tm_zone}
+members of the broken-down time
+structure. It uses the values of the other components to determine the
calendar time; it's permissible for these components to have
-unnormalized values outside of their normal ranges. The last thing that
+unnormalized values outside their normal ranges. The last thing that
@code{mktime} does is adjust the components of the @var{brokentime}
-structure (including the @code{tm_wday} and @code{tm_yday}).
+structure, including the members that were initially ignored.
-If the specified broken-down time cannot be represented as a calendar time,
+If the specified broken-down time cannot be represented as a simple time,
@code{mktime} returns a value of @code{(time_t)(-1)} and does not modify
the contents of @var{brokentime}.
-Calling @code{mktime} also sets the variable @code{tzname} with
-information about the current time zone. @xref{Time Zone Functions}.
+Calling @code{mktime} also sets the current time zone as if
+@code{tzset} were called; @code{mktime} uses this information instead
+of @var{brokentime}'s initial @code{tm_gmtoff} and @code{tm_zone}
+members. @xref{Time Zone Functions}.
+@end deftypefun
+
+@deftypefun time_t timelocal (struct tm *@var{brokentime})
+@standards{???, time.h}
+@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c Alias to mktime.
+
+@code{timelocal} is functionally identical to @code{mktime}, but more
+mnemonically named. Note that it is the inverse of the @code{localtime}
+function.
+
+@strong{Portability note:} @code{mktime} is essentially universally
+available. @code{timelocal} is rather rare.
+
+@end deftypefun
+
+@deftypefun time_t timegm (struct tm *@var{brokentime})
+@standards{???, time.h}
+@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c timegm @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c gmtime_offset triggers the same caveats as localtime_offset in mktime.
+@c although gmtime_r, as called by mktime, might save some issues,
+@c tzset calls tzset_internal with always, which forces
+@c reinitialization, so all issues may arise.
+@c tzset dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c mktime_internal(gmtime_r) @asulock @aculock
+@c ..gmtime_r @asulock @aculock
+@c ... dup ok
+@c tz_convert(!use_localtime) @asulock @aculock
+@c ... dup @asulock @aculock
+@c tzfile_compute(!use_localtime) ok
+
+@code{timegm} is functionally identical to @code{mktime} except it
+always takes the input values to be Coordinated Universal Time (UTC)
+regardless of any local time zone setting.
+
+Note that @code{timegm} is the inverse of @code{gmtime}.
+
+@strong{Portability note:} @code{mktime} is essentially universally
+available. @code{timegm} is rather rare. For the most portable
+conversion from a UTC broken-down time to a simple time, set
+the @code{TZ} environment variable to UTC, call @code{mktime}, then set
+@code{TZ} back.
+
+@end deftypefun
+
+
+
+@node High Accuracy Clock
+@subsection High Accuracy Clock
+
+@cindex time, high precision
+@cindex clock, high accuracy
+@pindex sys/timex.h
+@c On Linux, GNU libc implements ntp_gettime() and npt_adjtime() as calls
+@c to adjtimex().
+The @code{ntp_gettime} and @code{ntp_adjtime} functions provide an
+interface to monitor and manipulate the system clock to maintain high
+accuracy time. For example, you can fine tune the speed of the clock
+or synchronize it with another time source.
+
+A typical use of these functions is by a server implementing the Network
+Time Protocol to synchronize the clocks of multiple systems and high
+precision clocks.
+
+These functions are declared in @file{sys/timex.h}.
+
+@tindex struct ntptimeval
+@deftp {Data Type} {struct ntptimeval}
+This structure is used for information about the system clock. It
+contains the following members:
+@table @code
+@item struct timeval time
+This is the current calendar time, expressed as the elapsed time since
+the epoch. The @code{struct timeval} data type is described in
+@ref{Elapsed Time}.
+
+@item long int maxerror
+This is the maximum error, measured in microseconds. Unless updated
+via @code{ntp_adjtime} periodically, this value will reach some
+platform-specific maximum value.
+
+@item long int esterror
+This is the estimated error, measured in microseconds. This value can
+be set by @code{ntp_adjtime} to indicate the estimated offset of the
+system clock from the true calendar time.
+@end table
+@end deftp
+
+@deftypefun int ntp_gettime (struct ntptimeval *@var{tptr})
+@standards{GNU, sys/timex.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+@c Wrapper for adjtimex.
+The @code{ntp_gettime} function sets the structure pointed to by
+@var{tptr} to current values. The elements of the structure afterwards
+contain the values the timer implementation in the kernel assumes. They
+might or might not be correct. If they are not, an @code{ntp_adjtime}
+call is necessary.
+
+The return value is @code{0} on success and other values on failure. The
+following @code{errno} error conditions are defined for this function:
+
+@vtable @code
+@item TIME_ERROR
+The precision clock model is not properly set up at the moment, thus the
+clock must be considered unsynchronized, and the values should be
+treated with care.
+@end vtable
+@end deftypefun
+
+@tindex struct timex
+@deftp {Data Type} {struct timex}
+This structure is used to control and monitor the system clock. It
+contains the following members:
+@table @code
+@item unsigned int modes
+This variable controls whether and which values are set. Several
+symbolic constants have to be combined with @emph{binary or} to specify
+the effective mode. These constants start with @code{MOD_}.
+
+@item long int offset
+This value indicates the current offset of the system clock from the true
+calendar time. The value is given in microseconds. If bit
+@code{MOD_OFFSET} is set in @code{modes}, the offset (and possibly other
+dependent values) can be set. The offset's absolute value must not
+exceed @code{MAXPHASE}.
+
+
+@item long int frequency
+This value indicates the difference in frequency between the true
+calendar time and the system clock. The value is expressed as scaled
+PPM (parts per million, 0.0001%). The scaling is @code{1 <<
+SHIFT_USEC}. The value can be set with bit @code{MOD_FREQUENCY}, but
+the absolute value must not exceed @code{MAXFREQ}.
+
+@item long int maxerror
+This is the maximum error, measured in microseconds. A new value can be
+set using bit @code{MOD_MAXERROR}. Unless updated via
+@code{ntp_adjtime} periodically, this value will increase steadily
+and reach some platform-specific maximum value.
+
+@item long int esterror
+This is the estimated error, measured in microseconds. This value can
+be set using bit @code{MOD_ESTERROR}.
+
+@item int status
+This variable reflects the various states of the clock machinery. There
+are symbolic constants for the significant bits, starting with
+@code{STA_}. Some of these flags can be updated using the
+@code{MOD_STATUS} bit.
+
+@item long int constant
+This value represents the bandwidth or stiffness of the PLL (phase
+locked loop) implemented in the kernel. The value can be changed using
+bit @code{MOD_TIMECONST}.
+
+@item long int precision
+This value represents the accuracy or the maximum error when reading the
+system clock. The value is expressed in microseconds.
+
+@item long int tolerance
+This value represents the maximum frequency error of the system clock in
+scaled PPM. This value is used to increase the @code{maxerror} every
+second.
+
+@item struct timeval time
+The current calendar time.
+
+@item long int tick
+The elapsed time between clock ticks in microseconds. A clock tick is a
+periodic timer interrupt on which the system clock is based.
+
+@item long int ppsfreq
+This is the first of a few optional variables that are present only if
+the system clock can use a PPS (pulse per second) signal to discipline
+the system clock. The value is expressed in scaled PPM and it denotes
+the difference in frequency between the system clock and the PPS signal.
+
+@item long int jitter
+This value expresses a median filtered average of the PPS signal's
+dispersion in microseconds.
+
+@item int shift
+This value is a binary exponent for the duration of the PPS calibration
+interval, ranging from @code{PPS_SHIFT} to @code{PPS_SHIFTMAX}.
+
+@item long int stabil
+This value represents the median filtered dispersion of the PPS
+frequency in scaled PPM.
+
+@item long int jitcnt
+This counter represents the number of pulses where the jitter exceeded
+the allowed maximum @code{MAXTIME}.
+
+@item long int calcnt
+This counter reflects the number of successful calibration intervals.
+
+@item long int errcnt
+This counter represents the number of calibration errors (caused by
+large offsets or jitter).
+
+@item long int stbcnt
+This counter denotes the number of calibrations where the stability
+exceeded the threshold.
+@end table
+@end deftp
+
+@deftypefun int ntp_adjtime (struct timex *@var{tptr})
+@standards{GNU, sys/timex.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+@c Alias to adjtimex syscall.
+The @code{ntp_adjtime} function sets the structure specified by
+@var{tptr} to current values.
+
+In addition, @code{ntp_adjtime} updates some settings to match what you
+pass to it in *@var{tptr}. Use the @code{modes} element of *@var{tptr}
+to select what settings to update. You can set @code{offset},
+@code{freq}, @code{maxerror}, @code{esterror}, @code{status},
+@code{constant}, and @code{tick}.
+
+@code{modes} = zero means set nothing.
+
+Only the superuser can update settings.
+
+@c On Linux, ntp_adjtime() also does the adjtime() function if you set
+@c modes = ADJ_OFFSET_SINGLESHOT (in fact, that is how GNU libc implements
+@c adjtime()). But this should be considered an internal function because
+@c it's so inconsistent with the rest of what ntp_adjtime() does and is
+@c forced in an ugly way into the struct timex. So we don't document it
+@c and instead document adjtime() as the way to achieve the function.
+
+The return value is @code{0} on success and other values on failure. The
+following @code{errno} error conditions are defined for this function:
+
+@table @code
+@item TIME_ERROR
+The high accuracy clock model is not properly set up at the moment, thus the
+clock must be considered unsynchronized, and the values should be
+treated with care. Another reason could be that the specified new values
+are not allowed.
+
+@item EPERM
+The process specified a settings update, but is not superuser.
+
+@end table
+
+For more details see RFC1305 (Network Time Protocol, Version 3) and
+related documents.
+
+@strong{Portability note:} Early versions of @theglibc{} did not
+have this function but did have the synonymous @code{adjtimex}.
+
@end deftypefun
-@node Formatting Date and Time
-@subsection Formatting Date and Time
-The functions described in this section format time values as strings.
-These functions are declared in the header file @file{time.h}.
+@node Formatting Calendar Time
+@subsection Formatting Calendar Time
+
+The functions described in this section format calendar time values as
+strings. These functions are declared in the header file @file{time.h}.
@pindex time.h
-@comment time.h
-@comment ANSI
@deftypefun {char *} asctime (const struct tm *@var{brokentime})
+@standards{ISO, time.h}
+@safety{@prelim{}@mtunsafe{@mtasurace{:asctime} @mtslocale{}}@asunsafe{}@acsafe{}}
+@c asctime @mtasurace:asctime @mtslocale
+@c Uses a static buffer.
+@c asctime_internal @mtslocale
+@c snprintf dup @mtslocale [no @acsuheap @acsmem]
+@c ab_day_name @mtslocale
+@c ab_month_name @mtslocale
The @code{asctime} function converts the broken-down time value that
@var{brokentime} points to into a string in a standard format:
@smallexample
-"Tue May 21 13:46:22 1991\n"
+"Tue May 21 13:46:22 1991\n"
+@end smallexample
+
+The abbreviations for the days of week are: @samp{Sun}, @samp{Mon},
+@samp{Tue}, @samp{Wed}, @samp{Thu}, @samp{Fri}, and @samp{Sat}.
+
+The abbreviations for the months are: @samp{Jan}, @samp{Feb},
+@samp{Mar}, @samp{Apr}, @samp{May}, @samp{Jun}, @samp{Jul}, @samp{Aug},
+@samp{Sep}, @samp{Oct}, @samp{Nov}, and @samp{Dec}.
+
+The return value points to a statically allocated string, which might be
+overwritten by subsequent calls to @code{asctime} or @code{ctime}.
+(But no other library function overwrites the contents of this
+string.)
+@end deftypefun
+
+@deftypefun {char *} asctime_r (const struct tm *@var{brokentime}, char *@var{buffer})
+@standards{POSIX.1c, time.h}
+@safety{@prelim{}@mtsafe{@mtslocale{}}@assafe{}@acsafe{}}
+@c asctime_r @mtslocale
+@c asctime_internal dup @mtslocale
+This function is similar to @code{asctime} but instead of placing the
+result in a static buffer it writes the string in the buffer pointed to
+by the parameter @var{buffer}. This buffer should have room
+for at least 26 bytes, including the terminating null.
+
+If no error occurred the function returns a pointer to the string the
+result was written into, i.e., it returns @var{buffer}. Otherwise
+it returns @code{NULL}.
+@end deftypefun
+
+
+@deftypefun {char *} ctime (const time_t *@var{time})
+@standards{ISO, time.h}
+@safety{@prelim{}@mtunsafe{@mtasurace{:tmbuf} @mtasurace{:asctime} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c ctime @mtasurace:tmbuf @mtasurace:asctime @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c localtime dup @mtasurace:tmbuf @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c asctime dup @mtasurace:asctime @mtslocale
+The @code{ctime} function is similar to @code{asctime}, except that you
+specify the calendar time argument as a @code{time_t} simple time value
+rather than in broken-down local time format. It is equivalent to
+
+@smallexample
+asctime (localtime (@var{time}))
+@end smallexample
+
+Calling @code{ctime} also sets the current time zone as if
+@code{tzset} were called. @xref{Time Zone Functions}.
+@end deftypefun
+
+@deftypefun {char *} ctime_r (const time_t *@var{time}, char *@var{buffer})
+@standards{POSIX.1c, time.h}
+@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c ctime_r @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c asctime_r dup @mtslocale
+This function is similar to @code{ctime}, but places the result in the
+string pointed to by @var{buffer}. It is equivalent to (written using
+gcc extensions, @pxref{Statement Exprs,,,gcc,Porting and Using gcc}):
+
+@smallexample
+(@{ struct tm tm; asctime_r (localtime_r (time, &tm), buf); @})
+@end smallexample
+
+If no error occurred the function returns a pointer to the string the
+result was written into, i.e., it returns @var{buffer}. Otherwise
+it returns @code{NULL}.
+@end deftypefun
+
+
+@deftypefun size_t strftime (char *@var{s}, size_t @var{size}, const char *@var{template}, const struct tm *@var{brokentime})
+@standards{ISO, time.h}
+@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
+@c strftime @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
+@c strftime_l @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
+@c strftime_internal @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
+@c add ok
+@c memset_zero dup ok
+@c memset_space dup ok
+@c strlen dup ok
+@c mbrlen @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd [no @mtasurace:mbstate/!ps]
+@c mbsinit dup ok
+@c cpy ok
+@c add dup ok
+@c memcpy_lowcase ok
+@c TOLOWER ok
+@c tolower_l ok
+@c memcpy_uppcase ok
+@c TOUPPER ok
+@c toupper_l ok
+@c MEMCPY ok
+@c memcpy dup ok
+@c ISDIGIT ok
+@c STRLEN ok
+@c strlen dup ok
+@c strftime_internal dup @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
+@c TOUPPER dup ok
+@c nl_get_era_entry @ascuheap @asulock @acsmem @aculock
+@c nl_init_era_entries @ascuheap @asulock @acsmem @aculock
+@c libc_rwlock_wrlock dup @asulock @aculock
+@c malloc dup @ascuheap @acsmem
+@c memset dup ok
+@c free dup @ascuheap @acsmem
+@c realloc dup @ascuheap @acsmem
+@c memcpy dup ok
+@c strchr dup ok
+@c wcschr dup ok
+@c libc_rwlock_unlock dup @asulock @aculock
+@c ERA_DATE_CMP ok
+@c DO_NUMBER ok
+@c DO_NUMBER_SPACEPAD ok
+@c nl_get_alt_digit @ascuheap @asulock @acsmem @aculock
+@c libc_rwlock_wrlock dup @asulock @aculock
+@c nl_init_alt_digit @ascuheap @acsmem
+@c malloc dup @ascuheap @acsmem
+@c memset dup ok
+@c strchr dup ok
+@c libc_rwlock_unlock dup @aculock
+@c memset_space ok
+@c memset dup ok
+@c memset_zero ok
+@c memset dup ok
+@c mktime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c iso_week_days ok
+@c isleap ok
+@c tzset dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c gmtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c tm_diff ok
+This function is similar to the @code{sprintf} function (@pxref{Formatted
+Input}), but the conversion specifications that can appear in the format
+template @var{template} are specialized for printing components of the date
+and time @var{brokentime} according to the locale currently specified for
+time conversion (@pxref{Locales}) and the current time zone
+(@pxref{Time Zone Functions}).
+
+Ordinary characters appearing in the @var{template} are copied to the
+output string @var{s}; this can include multibyte character sequences.
+Conversion specifiers are introduced by a @samp{%} character, followed
+by an optional flag which can be one of the following. These flags
+are all GNU extensions. The first three affect only the output of
+numbers:
+
+@table @code
+@item _
+The number is padded with spaces.
+
+@item -
+The number is not padded at all.
+
+@item 0
+The number is padded with zeros even if the format specifies padding
+with spaces.
+
+@item ^
+The output uses uppercase characters, but only if this is possible
+(@pxref{Case Conversion}).
+@end table
+
+The default action is to pad the number with zeros to keep it a constant
+width. Numbers that do not have a range indicated below are never
+padded, since there is no natural width for them.
+
+Following the flag an optional specification of the width is possible.
+This is specified in decimal notation. If the natural size of the
+output of the field has less than the specified number of characters,
+the result is written right adjusted and space padded to the given
+size.
+
+An optional modifier can follow the optional flag and width
+specification. The modifiers, which were first standardized by
+POSIX.2-1992 and by @w{ISO C99}, are:
+
+@table @code
+@item E
+Use the locale's alternative representation for date and time. This
+modifier applies to the @code{%c}, @code{%C}, @code{%x}, @code{%X},
+@code{%y} and @code{%Y} format specifiers. In a Japanese locale, for
+example, @code{%Ex} might yield a date format based on the Japanese
+Emperors' reigns.
+
+@item O
+With all format specifiers that produce numbers: use the locale's
+alternative numeric symbols.
+
+With @code{%B}, @code{%b}, and @code{%h}: use the grammatical form for
+month names that is appropriate when the month is named by itself,
+rather than the form that is appropriate when the month is used as
+part of a complete date. This is a GNU extension.
+@end table
+
+If the format supports the modifier but no alternative representation
+is available, it is ignored.
+
+The conversion specifier ends with a format specifier taken from the
+following list. The whole @samp{%} sequence is replaced in the output
+string as follows:
+
+@table @code
+@item %a
+The abbreviated weekday name according to the current locale.
+
+@item %A
+The full weekday name according to the current locale.
+
+@item %b
+The abbreviated month name according to the current locale, in the
+grammatical form used when the month is part of a complete date.
+As a GNU extension, the @code{O} modifier can be used (@code{%Ob})
+to get the grammatical form used when the month is named by itself.
+
+@item %B
+The full month name according to the current locale, in the
+grammatical form used when the month is part of a complete date.
+As a GNU extension, the @code{O} modifier can be used (@code{%OB})
+to get the grammatical form used when the month is named by itself.
+
+Note that not all languages need two different forms of the month
+names, so the text produced by @code{%B} and @code{%OB}, and by
+@code{%b} and @code{%Ob}, may or may not be the same, depending on
+the locale.
+
+@item %c
+The preferred calendar time representation for the current locale.
+
+@item %C
+The century of the year. This is equivalent to the greatest integer not
+greater than the year divided by 100.
+
+If the @code{E} modifier is specified (@code{%EC}), instead produces
+the name of the period for the year (e.g.@: an era name) in the
+locale's alternative calendar.
+
+This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
+
+@item %d
+The day of the month as a decimal number (range @code{01} through @code{31}).
+
+@item %D
+The date using the format @code{%m/%d/%y}.
+
+This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
+
+@item %e
+The day of the month like with @code{%d}, but padded with spaces (range
+@code{ 1} through @code{31}).
+
+This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
+
+@item %F
+The date using the format @code{%Y-%m-%d}. This is the form specified
+in the @w{ISO 8601} standard and is the preferred form for all uses.
+
+This format was first standardized by @w{ISO C99} and by POSIX.1-2001.
+
+@item %g
+The year corresponding to the ISO week number, but without the century
+(range @code{00} through @code{99}). This has the same format and value
+as @code{%y}, except that if the ISO week number (see @code{%V}) belongs
+to the previous or next year, that year is used instead.
+
+This format was first standardized by @w{ISO C99} and by POSIX.1-2001.
+
+@item %G
+The year corresponding to the ISO week number. This has the same format
+and value as @code{%Y}, except that if the ISO week number (see
+@code{%V}) belongs to the previous or next year, that year is used
+instead.
+
+This format was first standardized by @w{ISO C99} and by POSIX.1-2001
+but was previously available as a GNU extension.
+
+@item %h
+The abbreviated month name according to the current locale. The action
+is the same as for @code{%b}.
+
+This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
+
+@item %H
+The hour as a decimal number, using a 24-hour clock (range @code{00} through
+@code{23}).
+
+@item %I
+The hour as a decimal number, using a 12-hour clock (range @code{01} through
+@code{12}).
+
+@item %j
+The day of the year as a decimal number (range @code{001} through @code{366}).
+
+@item %k
+The hour as a decimal number, using a 24-hour clock like @code{%H}, but
+padded with spaces (range @code{ 0} through @code{23}).
+
+This format is a GNU extension.
+
+@item %l
+The hour as a decimal number, using a 12-hour clock like @code{%I}, but
+padded with spaces (range @code{ 1} through @code{12}).
+
+This format is a GNU extension.
+
+@item %m
+The month as a decimal number (range @code{01} through @code{12}).
+
+@item %M
+The minute as a decimal number (range @code{00} through @code{59}).
+
+@item %n
+A single @samp{\n} (newline) character.
+
+This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
+
+@item %p
+Either @samp{AM} or @samp{PM}, according to the given time value; or the
+corresponding strings for the current locale. Noon is treated as
+@samp{PM} and midnight as @samp{AM}. In most locales
+@samp{AM}/@samp{PM} format is not supported, in such cases @code{"%p"}
+yields an empty string.
+
+@ignore
+We currently have a problem with makeinfo. Write @samp{AM} and @samp{am}
+both results in `am'. I.e., the difference in case is not visible anymore.
+@end ignore
+@item %P
+Either @samp{am} or @samp{pm}, according to the given time value; or the
+corresponding strings for the current locale, printed in lowercase
+characters. Noon is treated as @samp{pm} and midnight as @samp{am}. In
+most locales @samp{AM}/@samp{PM} format is not supported, in such cases
+@code{"%P"} yields an empty string.
+
+This format is a GNU extension.
+
+@item %r
+The complete calendar time using the AM/PM format of the current locale.
+
+This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
+In the POSIX locale, this format is equivalent to @code{%I:%M:%S %p}.
+
+@item %R
+The hour and minute in decimal numbers using the format @code{%H:%M}.
+
+This format was first standardized by @w{ISO C99} and by POSIX.1-2001
+but was previously available as a GNU extension.
+
+@item %s
+The number of seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
+Leap seconds are not counted unless leap second support is available.
+
+This format is a GNU extension.
+
+@item %S
+The seconds as a decimal number (range @code{00} through @code{60}).
+
+@item %t
+A single @samp{\t} (tabulator) character.
+
+This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
+
+@item %T
+The time of day using decimal numbers using the format @code{%H:%M:%S}.
+
+This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
+
+@item %u
+The day of the week as a decimal number (range @code{1} through
+@code{7}), Monday being @code{1}.
+
+This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
+
+@item %U
+The week number of the current year as a decimal number (range @code{00}
+through @code{53}), starting with the first Sunday as the first day of
+the first week. Days preceding the first Sunday in the year are
+considered to be in week @code{00}.
+
+@item %V
+The @w{ISO 8601:1988} week number as a decimal number (range @code{01}
+through @code{53}). ISO weeks start with Monday and end with Sunday.
+Week @code{01} of a year is the first week which has the majority of its
+days in that year; this is equivalent to the week containing the year's
+first Thursday, and it is also equivalent to the week containing January
+4. Week @code{01} of a year can contain days from the previous year.
+The week before week @code{01} of a year is the last week (@code{52} or
+@code{53}) of the previous year even if it contains days from the new
+year.
+
+This format was first standardized by POSIX.2-1992 and by @w{ISO C99}.
+
+@item %w
+The day of the week as a decimal number (range @code{0} through
+@code{6}), Sunday being @code{0}.
+
+@item %W
+The week number of the current year as a decimal number (range @code{00}
+through @code{53}), starting with the first Monday as the first day of
+the first week. All days preceding the first Monday in the year are
+considered to be in week @code{00}.
+
+@item %x
+The preferred date representation for the current locale.
+
+@item %X
+The preferred time of day representation for the current locale.
+
+@item %y
+The year without a century as a decimal number (range @code{00} through
+@code{99}). This is equivalent to the year modulo 100.
+
+If the @code{E} modifier is specified (@code{%Ey}), instead produces
+the year number according to a locale-specific alternative calendar.
+Unlike @code{%y}, the number is @emph{not} reduced modulo 100.
+However, by default it is zero-padded to a minimum of two digits (this
+can be overridden by an explicit field width or by the @code{_} and
+@code{-} flags).
+
+@item %Y
+The year as a decimal number, using the Gregorian calendar. Years
+before the year @code{1} are numbered @code{0}, @code{-1}, and so on.
+
+If the @code{E} modifier is specified (@code{%EY}), instead produces a
+complete representation of the year according to the locale's
+alternative calendar. Generally this will be some combination of the
+information produced by @code{%EC} and @code{%Ey}. As a GNU
+extension, the formatting flags @code{_} or @code{-} may be used with
+this conversion specifier; they affect how the year number is printed.
+
+@item %z
+@w{RFC 822}/@w{ISO 8601:1988} style numeric time zone (e.g.,
+@code{-0600} or @code{+0100}), or nothing if no time zone is
+determinable.
+
+This format was first standardized by @w{ISO C99} and by POSIX.1-2001
+but was previously available as a GNU extension.
+
+In the POSIX locale, a full @w{RFC 822} timestamp is generated by the format
+@w{@samp{"%a, %d %b %Y %H:%M:%S %z"}} (or the equivalent
+@w{@samp{"%a, %d %b %Y %T %z"}}).
+
+@item %Z
+The time zone abbreviation (empty if the time zone can't be determined).
+
+@item %%
+A literal @samp{%} character.
+@end table
+
+The @var{size} parameter can be used to specify the maximum number of
+characters to be stored in the array @var{s}, including the terminating
+null character. If the formatted time requires more than @var{size}
+characters, @code{strftime} returns zero and the contents of the array
+@var{s} are undefined. Otherwise the return value indicates the
+number of characters placed in the array @var{s}, not including the
+terminating null character.
+
+@emph{Warning:} This convention for the return value which is prescribed
+in @w{ISO C} can lead to problems in some situations. For certain
+format strings and certain locales the output really can be the empty
+string and this cannot be discovered by testing the return value only.
+E.g., in most locales the AM/PM time format is not supported (most of
+the world uses the 24 hour time representation). In such locales
+@code{"%p"} will return the empty string, i.e., the return value is
+zero. To detect situations like this something similar to the following
+code should be used:
+
+@smallexample
+buf[0] = '\1';
+len = strftime (buf, bufsize, format, tp);
+if (len == 0 && buf[0] != '\0')
+ @{
+ /* Something went wrong in the strftime call. */
+ @dots{}
+ @}
@end smallexample
-The abbreviations for the days of week are: @samp{Sun}, @samp{Mon},
-@samp{Tue}, @samp{Wed}, @samp{Thu}, @samp{Fri}, and @samp{Sat}.
+If @var{s} is a null pointer, @code{strftime} does not actually write
+anything, but instead returns the number of characters it would have written.
-The abbreviations for the months are: @samp{Jan}, @samp{Feb},
-@samp{Mar}, @samp{Apr}, @samp{May}, @samp{Jun}, @samp{Jul}, @samp{Aug},
-@samp{Sep}, @samp{Oct}, @samp{Nov}, and @samp{Dec}.
+Calling @code{strftime} also sets the current time zone as if
+@code{tzset} were called; @code{strftime} uses this information
+instead of @var{brokentime}'s @code{tm_gmtoff} and @code{tm_zone}
+members. @xref{Time Zone Functions}.
-The return value points to a statically allocated string, which might be
-overwritten by subsequent calls to @code{asctime} or @code{ctime}.
-(But no other library function overwrites the contents of this
-string.)
+For an example of @code{strftime}, see @ref{Time Functions Example}.
@end deftypefun
-@comment time.h
-@comment ANSI
-@deftypefun {char *} ctime (const time_t *@var{time})
-The @code{ctime} function is similar to @code{asctime}, except that the
-time value is specified as a @code{time_t} calendar time value rather
-than in broken-down local time format. It is equivalent to
+@deftypefun size_t wcsftime (wchar_t *@var{s}, size_t @var{size}, const wchar_t *@var{template}, const struct tm *@var{brokentime})
+@standards{ISO/Amend1, time.h}
+@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@asucorrupt{} @ascuheap{} @asulock{} @ascudlopen{}}@acunsafe{@acucorrupt{} @aculock{} @acsmem{} @acsfd{}}}
+@c wcsftime @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
+@c wcsftime_l @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
+@c wcsftime_internal @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
+@c add ok
+@c memset_zero dup ok
+@c memset_space dup ok
+@c wcslen dup ok
+@c cpy ok
+@c add dup ok
+@c memcpy_lowcase ok
+@c TOLOWER ok
+@c towlower_l dup ok
+@c memcpy_uppcase ok
+@c TOUPPER ok
+@c towupper_l dup ok
+@c MEMCPY ok
+@c wmemcpy dup ok
+@c widen @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
+@c memset dup ok
+@c mbsrtowcs_l @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd [no @mtasurace:mbstate/!ps]
+@c ISDIGIT ok
+@c STRLEN ok
+@c wcslen dup ok
+@c wcsftime_internal dup @mtsenv @mtslocale @asucorrupt @ascuheap @asulock @ascudlopen @acucorrupt @aculock @acsmem @acsfd
+@c TOUPPER dup ok
+@c nl_get_era_entry dup @ascuheap @asulock @acsmem @aculock
+@c DO_NUMBER ok
+@c DO_NUMBER_SPACEPAD ok
+@c nl_get_walt_digit dup @ascuheap @asulock @acsmem @aculock
+@c libc_rwlock_wrlock dup @asulock @aculock
+@c nl_init_alt_digit dup @ascuheap @acsmem
+@c malloc dup @ascuheap @acsmem
+@c memset dup ok
+@c wcschr dup ok
+@c libc_rwlock_unlock dup @aculock
+@c memset_space ok
+@c wmemset dup ok
+@c memset_zero ok
+@c wmemset dup ok
+@c mktime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c iso_week_days ok
+@c isleap ok
+@c tzset dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c gmtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c tm_diff ok
+The @code{wcsftime} function is equivalent to the @code{strftime}
+function with the difference that it operates on wide character
+strings. The buffer where the result is stored, pointed to by @var{s},
+must be an array of wide characters. The parameter @var{size} which
+specifies the size of the output buffer gives the number of wide
+characters, not the number of bytes.
+
+Also the format string @var{template} is a wide character string. Since
+all characters needed to specify the format string are in the basic
+character set it is portably possible to write format strings in the C
+source code using the @code{L"@dots{}"} notation. The parameter
+@var{brokentime} has the same meaning as in the @code{strftime} call.
+
+The @code{wcsftime} function supports the same flags, modifiers, and
+format specifiers as the @code{strftime} function.
+
+The return value of @code{wcsftime} is the number of wide characters
+stored in @code{s}. When more characters would have to be written than
+can be placed in the buffer @var{s} the return value is zero, with the
+same problems indicated in the @code{strftime} documentation.
+@end deftypefun
-@smallexample
-asctime (localtime (@var{time}))
-@end smallexample
+@node Parsing Date and Time
+@subsection Convert textual time and date information back
-@code{ctime} sets the variable @code{tzname}, because @code{localtime}
-does so. @xref{Time Zone Functions}.
-@end deftypefun
+The @w{ISO C} standard does not specify any functions which can convert
+the output of the @code{strftime} function back into a binary format.
+This led to a variety of more-or-less successful implementations with
+different interfaces over the years. Then the Unix standard was
+extended by the addition of two functions: @code{strptime} and
+@code{getdate}. Both have strange interfaces but at least they are
+widely available.
-@comment time.h
-@comment ANSI
-@deftypefun size_t strftime (char *@var{s}, size_t @var{size}, const char *@var{template}, const struct tm *@var{brokentime})
-This function is similar to the @code{sprintf} function (@pxref{Formatted
-Input}), but the conversion specifications that can appear in the format
-template @var{template} are specialized for printing components of the date
-and time @var{brokentime} according to the locale currently specified for
-time conversion (@pxref{Locales}).
+@menu
+* Low-Level Time String Parsing:: Interpret string according to given format.
+* General Time String Parsing:: User-friendly function to parse data and
+ time strings.
+@end menu
-Ordinary characters appearing in the @var{template} are copied to the
-output string @var{s}; this can include multibyte character sequences.
-Conversion specifiers are introduced by a @samp{%} character, and are
-replaced in the output string as follows:
+@node Low-Level Time String Parsing
+@subsubsection Interpret string according to given format
+
+The first function is rather low-level. It is nevertheless frequently
+used in software since it is better known. Its interface and
+implementation are heavily influenced by the @code{getdate} function,
+which is defined and implemented in terms of calls to @code{strptime}.
+
+@deftypefun {char *} strptime (const char *@var{s}, const char *@var{fmt}, struct tm *@var{tp})
+@standards{XPG4, time.h}
+@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c strptime @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c strptime_internal @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c memset dup ok
+@c ISSPACE ok
+@c isspace_l dup ok
+@c match_char ok
+@c match_string ok
+@c strlen dup ok
+@c strncasecmp_l dup ok
+@c strcmp dup ok
+@c recursive @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c strptime_internal dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c get_number ok
+@c ISSPACE dup ok
+@c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c nl_select_era_entry @ascuheap @asulock @acsmem @aculock
+@c nl_init_era_entries dup @ascuheap @asulock @acsmem @aculock
+@c get_alt_number dup @ascuheap @asulock @acsmem @aculock
+@c nl_parse_alt_digit dup @ascuheap @asulock @acsmem @aculock
+@c libc_rwlock_wrlock dup @asulock @aculock
+@c nl_init_alt_digit dup @ascuheap @acsmem
+@c libc_rwlock_unlock dup @aculock
+@c get_number dup ok
+@c day_of_the_week ok
+@c day_of_the_year ok
+The @code{strptime} function parses the input string @var{s} according
+to the format string @var{fmt} and stores its results in the
+structure @var{tp}.
+
+The input string could be generated by a @code{strftime} call or
+obtained any other way. It does not need to be in a human-recognizable
+format; e.g. a date passed as @code{"02:1999:9"} is acceptable, even
+though it is ambiguous without context. As long as the format string
+@var{fmt} matches the input string the function will succeed.
+
+The user has to make sure, though, that the input can be parsed in a
+unambiguous way. The string @code{"1999112"} can be parsed using the
+format @code{"%Y%m%d"} as 1999-1-12, 1999-11-2, or even 19991-1-2. It
+is necessary to add appropriate separators to reliably get results.
+
+The format string consists of the same components as the format string
+of the @code{strftime} function. The only difference is that the flags
+@code{_}, @code{-}, @code{0}, and @code{^} are not allowed.
+@comment Is this really the intention? --drepper
+Several of the distinct formats of @code{strftime} do the same work in
+@code{strptime} since differences like case of the input do not matter.
+For reasons of symmetry all formats are supported, though.
+
+The modifiers @code{E} and @code{O} are also allowed everywhere the
+@code{strftime} function allows them.
+
+The formats are:
@table @code
@item %a
-The abbreviated weekday name according to the current locale.
-
-@item %A
-The full weekday name according to the current locale.
+@itemx %A
+The weekday name according to the current locale, in abbreviated form or
+the full name.
@item %b
-The abbreviated month name according to the current locale.
+@itemx %B
+@itemx %h
+A month name according to the current locale. All three specifiers
+will recognize both abbreviated and full month names. If the
+locale provides two different grammatical forms of month names,
+all three specifiers will recognize both forms.
-@item %B
-The full month name according to the current locale.
+As a GNU extension, the @code{O} modifier can be used with these
+specifiers; it has no effect, as both grammatical forms of month
+names are recognized.
@item %c
-The preferred date and time representation for the current locale.
+The date and time representation for the current locale.
+
+@item %Ec
+Like @code{%c} but the locale's alternative date and time format is used.
+
+@item %C
+The century of the year.
+
+It makes sense to use this format only if the format string also
+contains the @code{%y} format.
+
+@item %EC
+The locale's representation of the period.
+
+Unlike @code{%C} it sometimes makes sense to use this format since some
+cultures represent years relative to the beginning of eras instead of
+using the Gregorian years.
@item %d
-The day of the month as a decimal number (range @code{01} to @code{31}).
+@item %e
+The day of the month as a decimal number (range @code{1} through @code{31}).
+Leading zeroes are permitted but not required.
+
+@item %Od
+@itemx %Oe
+Same as @code{%d} but using the locale's alternative numeric symbols.
+
+Leading zeroes are permitted but not required.
+
+@item %D
+Equivalent to @code{%m/%d/%y}.
+
+@item %F
+Equivalent to @code{%Y-%m-%d}, which is the @w{ISO 8601} date
+format.
+
+This is a GNU extension following an @w{ISO C99} extension to
+@code{strftime}.
+
+@item %g
+The year corresponding to the ISO week number, but without the century
+(range @code{00} through @code{99}).
+
+@emph{Note:} Currently, this is not fully implemented. The format is
+recognized, input is consumed but no field in @var{tm} is set.
+
+This format is a GNU extension following a GNU extension of @code{strftime}.
+
+@item %G
+The year corresponding to the ISO week number.
+
+@emph{Note:} Currently, this is not fully implemented. The format is
+recognized, input is consumed but no field in @var{tm} is set.
+
+This format is a GNU extension following a GNU extension of @code{strftime}.
@item %H
-The hour as a decimal number, using a 24-hour clock (range @code{00} to
+@itemx %k
+The hour as a decimal number, using a 24-hour clock (range @code{00} through
@code{23}).
+@code{%k} is a GNU extension following a GNU extension of @code{strftime}.
+
+@item %OH
+Same as @code{%H} but using the locale's alternative numeric symbols.
+
@item %I
-The hour as a decimal number, using a 12-hour clock (range @code{01} to
+@itemx %l
+The hour as a decimal number, using a 12-hour clock (range @code{01} through
@code{12}).
+@code{%l} is a GNU extension following a GNU extension of @code{strftime}.
+
+@item %OI
+Same as @code{%I} but using the locale's alternative numeric symbols.
+
@item %j
-The day of the year as a decimal number (range @code{001} to @code{366}).
+The day of the year as a decimal number (range @code{1} through @code{366}).
+
+Leading zeroes are permitted but not required.
@item %m
-The month as a decimal number (range @code{01} to @code{12}).
+The month as a decimal number (range @code{1} through @code{12}).
+
+Leading zeroes are permitted but not required.
+
+@item %Om
+Same as @code{%m} but using the locale's alternative numeric symbols.
@item %M
-The minute as a decimal number.
+The minute as a decimal number (range @code{0} through @code{59}).
+
+Leading zeroes are permitted but not required.
+
+@item %OM
+Same as @code{%M} but using the locale's alternative numeric symbols.
+
+@item %n
+@itemx %t
+Matches any white space.
@item %p
-Either @samp{am} or @samp{pm}, according to the given time value; or the
-corresponding strings for the current locale.
+@item %P
+The locale-dependent equivalent to @samp{AM} or @samp{PM}.
+
+This format is not useful unless @code{%I} or @code{%l} is also used.
+Another complication is that the locale might not define these values at
+all and therefore the conversion fails.
+
+@code{%P} is a GNU extension following a GNU extension to @code{strftime}.
+
+@item %r
+The complete time using the AM/PM format of the current locale.
+
+A complication is that the locale might not define this format at all
+and therefore the conversion fails.
+
+@item %R
+The hour and minute in decimal numbers using the format @code{%H:%M}.
+
+@code{%R} is a GNU extension following a GNU extension to @code{strftime}.
+
+@item %s
+The number of seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
+Leap seconds are not counted unless leap second support is available.
+
+@code{%s} is a GNU extension following a GNU extension to @code{strftime}.
@item %S
-The second as a decimal number.
+The seconds as a decimal number (range @code{0} through @code{60}).
+
+Leading zeroes are permitted but not required.
+
+@strong{NB:} The Unix specification says the upper bound on this value
+is @code{61}, a result of a decision to allow double leap seconds. You
+will not see the value @code{61} because no minute has more than one
+leap second, but the myth persists.
+
+@item %OS
+Same as @code{%S} but using the locale's alternative numeric symbols.
+
+@item %T
+Equivalent to the use of @code{%H:%M:%S} in this place.
+
+@item %u
+The day of the week as a decimal number (range @code{1} through
+@code{7}), Monday being @code{1}.
+
+Leading zeroes are permitted but not required.
+
+@emph{Note:} Currently, this is not fully implemented. The format is
+recognized, input is consumed but no field in @var{tm} is set.
@item %U
-The week number of the current year as a decimal number, starting with
-the first Sunday as the first day of the first week.
+The week number of the current year as a decimal number (range @code{0}
+through @code{53}).
-@item %W
-The week number of the current year as a decimal number, starting with
-the first Monday as the first day of the first week.
+Leading zeroes are permitted but not required.
+
+@item %OU
+Same as @code{%U} but using the locale's alternative numeric symbols.
+
+@item %V
+The @w{ISO 8601:1988} week number as a decimal number (range @code{1}
+through @code{53}).
+
+Leading zeroes are permitted but not required.
+
+@emph{Note:} Currently, this is not fully implemented. The format is
+recognized, input is consumed but no field in @var{tm} is set.
@item %w
-The day of the week as a decimal number, Sunday being @code{0}.
+The day of the week as a decimal number (range @code{0} through
+@code{6}), Sunday being @code{0}.
+
+Leading zeroes are permitted but not required.
+
+@emph{Note:} Currently, this is not fully implemented. The format is
+recognized, input is consumed but no field in @var{tm} is set.
+
+@item %Ow
+Same as @code{%w} but using the locale's alternative numeric symbols.
+
+@item %W
+The week number of the current year as a decimal number (range @code{0}
+through @code{53}).
+
+Leading zeroes are permitted but not required.
+
+@emph{Note:} Currently, this is not fully implemented. The format is
+recognized, input is consumed but no field in @var{tm} is set.
+
+@item %OW
+Same as @code{%W} but using the locale's alternative numeric symbols.
@item %x
-The preferred date representation for the current locale, but without the
-time.
+The date using the locale's date format.
+
+@item %Ex
+Like @code{%x} but the locale's alternative data representation is used.
@item %X
-The preferred time representation for the current locale, but with no date.
+The time using the locale's time format.
+
+@item %EX
+Like @code{%X} but the locale's alternative time representation is used.
@item %y
-The year as a decimal number, but without a century (range @code{00} to
+The year without a century as a decimal number (range @code{0} through
@code{99}).
+Leading zeroes are permitted but not required.
+
+Note that it is questionable to use this format without
+the @code{%C} format. The @code{strptime} function does regard input
+values in the range @math{68} to @math{99} as the years @math{1969} to
+@math{1999} and the values @math{0} to @math{68} as the years
+@math{2000} to @math{2068}. But maybe this heuristic fails for some
+input data.
+
+Therefore it is best to avoid @code{%y} completely and use @code{%Y}
+instead.
+
+@item %Ey
+The offset from @code{%EC} in the locale's alternative representation.
+
+@item %Oy
+The offset of the year (from @code{%C}) using the locale's alternative
+numeric symbols.
+
@item %Y
-The year as a decimal number, including the century.
+The year as a decimal number, using the Gregorian calendar.
+
+@item %EY
+The full alternative year representation.
+
+@item %z
+The offset from GMT in @w{ISO 8601}/RFC822 format.
@item %Z
-The time zone or name or abbreviation (empty if the time zone can't be
-determined).
+The timezone name.
+
+@emph{Note:} Currently, this is not fully implemented. The format is
+recognized, input is consumed but no field in @var{tm} is set.
@item %%
A literal @samp{%} character.
@end table
-The @var{size} parameter can be used to specify the maximum number of
-characters to be stored in the array @var{s}, including the terminating
-null character. If the formatted time requires more than @var{size}
-characters, the excess characters are discarded. The return value from
-@code{strftime} is the number of characters placed in the array @var{s},
-not including the terminating null character. If the value equals
-@var{size}, it means that the array @var{s} was too small; you should
-repeat the call, providing a bigger array.
+All other characters in the format string must have a matching character
+in the input string. Exceptions are white spaces in the input string
+which can match zero or more whitespace characters in the format string.
+
+@strong{Portability Note:} The XPG standard advises applications to use
+at least one whitespace character (as specified by @code{isspace}) or
+other non-alphanumeric characters between any two conversion
+specifications. @Theglibc{} does not have this limitation but
+other libraries might have trouble parsing formats like
+@code{"%d%m%Y%H%M%S"}.
+
+The @code{strptime} function processes the input string from right to
+left. Each of the three possible input elements (white space, literal,
+or format) are handled one after the other. If the input cannot be
+matched to the format string the function stops. The remainder of the
+format and input strings are not processed.
+
+The function returns a pointer to the first character it was unable to
+process. If the input string contains more characters than required by
+the format string the return value points right after the last consumed
+input character. If the whole input string is consumed the return value
+points to the @code{NULL} byte at the end of the string. If an error
+occurs, i.e., @code{strptime} fails to match all of the format string,
+the function returns @code{NULL}.
+@end deftypefun
-If @var{s} is a null pointer, @code{strftime} does not actually write
-anything, but instead returns the number of characters it would have written.
+The specification of the function in the XPG standard is rather vague,
+leaving out a few important pieces of information. Most importantly, it
+does not specify what happens to those elements of @var{tm} which are
+not directly initialized by the different formats. The
+implementations on different Unix systems vary here.
-For an example of @code{strftime}, see @ref{Time Functions Example}.
+The @glibcadj{} implementation does not touch those fields which are not
+directly initialized. Exceptions are the @code{tm_wday} and
+@code{tm_yday} elements, which are recomputed if any of the year, month,
+or date elements changed. This has two implications:
+
+@itemize @bullet
+@item
+Before calling the @code{strptime} function for a new input string, you
+should prepare the @var{tm} structure you pass. Normally this will mean
+initializing all values to zero. Alternatively, you can set all
+fields to values like @code{INT_MAX}, allowing you to determine which
+elements were set by the function call. Zero does not work here since
+it is a valid value for many of the fields.
+
+Careful initialization is necessary if you want to find out whether a
+certain field in @var{tm} was initialized by the function call.
+
+@item
+You can construct a @code{struct tm} value with several consecutive
+@code{strptime} calls. A useful application of this is e.g. the parsing
+of two separate strings, one containing date information and the other
+time information. By parsing one after the other without clearing the
+structure in-between, you can construct a complete broken-down time.
+@end itemize
+
+The following example shows a function which parses a string which
+contains the date information in either US style or @w{ISO 8601} form:
+
+@smallexample
+const char *
+parse_date (const char *input, struct tm *tm)
+@{
+ const char *cp;
+
+ /* @r{First clear the result structure.} */
+ memset (tm, '\0', sizeof (*tm));
+
+ /* @r{Try the ISO format first.} */
+ cp = strptime (input, "%F", tm);
+ if (cp == NULL)
+ @{
+ /* @r{Does not match. Try the US form.} */
+ cp = strptime (input, "%D", tm);
+ @}
+
+ return cp;
+@}
+@end smallexample
+
+@node General Time String Parsing
+@subsubsection A More User-friendly Way to Parse Times and Dates
+
+The Unix standard defines another function for parsing date strings.
+The interface is weird, but if the function happens to suit your
+application it is just fine. It is problematic to use this function
+in multi-threaded programs or libraries, since it returns a pointer to
+a static variable, and uses a global variable and global state (an
+environment variable).
+
+@defvar getdate_err
+@standards{Unix98, time.h}
+This variable of type @code{int} contains the error code of the last
+unsuccessful call to @code{getdate}. Defined values are:
+
+@table @math
+@item 1
+The environment variable @code{DATEMSK} is not defined or null.
+@item 2
+The template file denoted by the @code{DATEMSK} environment variable
+cannot be opened.
+@item 3
+Information about the template file cannot retrieved.
+@item 4
+The template file is not a regular file.
+@item 5
+An I/O error occurred while reading the template file.
+@item 6
+Not enough memory available to execute the function.
+@item 7
+The template file contains no matching template.
+@item 8
+The input date is invalid, but would match a template otherwise. This
+includes dates like February 31st, and dates which cannot be represented
+in a @code{time_t} variable.
+@end table
+@end defvar
+
+@deftypefun {struct tm *} getdate (const char *@var{string})
+@standards{Unix98, time.h}
+@safety{@prelim{}@mtunsafe{@mtasurace{:getdate} @mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c getdate @mtasurace:getdate @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c getdate_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+The interface to @code{getdate} is the simplest possible for a function
+to parse a string and return the value. @var{string} is the input
+string and the result is returned in a statically-allocated variable.
+
+The details about how the string is processed are hidden from the user.
+In fact, they can be outside the control of the program. Which formats
+are recognized is controlled by the file named by the environment
+variable @code{DATEMSK}. This file should contain
+lines of valid format strings which could be passed to @code{strptime}.
+
+The @code{getdate} function reads these format strings one after the
+other and tries to match the input string. The first line which
+completely matches the input string is used.
+
+Elements not initialized through the format string retain the values
+present at the time of the @code{getdate} function call.
+
+The formats recognized by @code{getdate} are the same as for
+@code{strptime}. See above for an explanation. There are only a few
+extensions to the @code{strptime} behavior:
+
+@itemize @bullet
+@item
+If the @code{%Z} format is given the broken-down time is based on the
+current time of the timezone matched, not of the current timezone of the
+runtime environment.
+
+@emph{Note}: This is not implemented (currently). The problem is that
+timezone names are not unique. If a fixed timezone is assumed for a
+given string (say @code{EST} meaning US East Coast time), then uses for
+countries other than the USA will fail. So far we have found no good
+solution to this.
+
+@item
+If only the weekday is specified the selected day depends on the current
+date. If the current weekday is greater than or equal to the @code{tm_wday}
+value the current week's day is chosen, otherwise the day next week is chosen.
+
+@item
+A similar heuristic is used when only the month is given and not the
+year. If the month is greater than or equal to the current month, then
+the current year is used. Otherwise it wraps to next year. The first
+day of the month is assumed if one is not explicitly specified.
+
+@item
+The current hour, minute, and second are used if the appropriate value is
+not set through the format.
+
+@item
+If no date is given tomorrow's date is used if the time is
+smaller than the current time. Otherwise today's date is taken.
+@end itemize
+
+It should be noted that the format in the template file need not only
+contain format elements. The following is a list of possible format
+strings (taken from the Unix standard):
+
+@smallexample
+%m
+%A %B %d, %Y %H:%M:%S
+%A
+%B
+%m/%d/%y %I %p
+%d,%m,%Y %H:%M
+at %A the %dst of %B in %Y
+run job at %I %p,%B %dnd
+%A den %d. %B %Y %H.%M Uhr
+@end smallexample
+
+As you can see, the template list can contain very specific strings like
+@code{run job at %I %p,%B %dnd}. Using the above list of templates and
+assuming the current time is Mon Sep 22 12:19:47 EDT 1986, we can obtain the
+following results for the given input.
+
+@multitable {xxxxxxxxxxxx} {xxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx}
+@item Input @tab Match @tab Result
+@item Mon @tab %a @tab Mon Sep 22 12:19:47 EDT 1986
+@item Sun @tab %a @tab Sun Sep 28 12:19:47 EDT 1986
+@item Fri @tab %a @tab Fri Sep 26 12:19:47 EDT 1986
+@item September @tab %B @tab Mon Sep 1 12:19:47 EDT 1986
+@item January @tab %B @tab Thu Jan 1 12:19:47 EST 1987
+@item December @tab %B @tab Mon Dec 1 12:19:47 EST 1986
+@item Sep Mon @tab %b %a @tab Mon Sep 1 12:19:47 EDT 1986
+@item Jan Fri @tab %b %a @tab Fri Jan 2 12:19:47 EST 1987
+@item Dec Mon @tab %b %a @tab Mon Dec 1 12:19:47 EST 1986
+@item Jan Wed 1989 @tab %b %a %Y @tab Wed Jan 4 12:19:47 EST 1989
+@item Fri 9 @tab %a %H @tab Fri Sep 26 09:00:00 EDT 1986
+@item Feb 10:30 @tab %b %H:%S @tab Sun Feb 1 10:00:30 EST 1987
+@item 10:30 @tab %H:%M @tab Tue Sep 23 10:30:00 EDT 1986
+@item 13:30 @tab %H:%M @tab Mon Sep 22 13:30:00 EDT 1986
+@end multitable
+
+The return value of the function is a pointer to a static variable of
+type @w{@code{struct tm}}, or a null pointer if an error occurred. The
+result is only valid until the next @code{getdate} call, making this
+function unusable in multi-threaded applications.
+
+The @code{errno} variable is @emph{not} changed. Error conditions are
+stored in the global variable @code{getdate_err}. See the
+description above for a list of the possible error values.
+
+@emph{Warning:} The @code{getdate} function should @emph{never} be
+used in SUID-programs. The reason is obvious: using the
+@code{DATEMSK} environment variable you can get the function to open
+any arbitrary file and chances are high that with some bogus input
+(such as a binary file) the program will crash.
+@end deftypefun
+
+@deftypefun int getdate_r (const char *@var{string}, struct tm *@var{tp})
+@standards{GNU, time.h}
+@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c getdate_r @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c getenv dup @mtsenv
+@c stat64 dup ok
+@c access dup ok
+@c fopen dup @ascuheap @asulock @acsmem @acsfd @aculock
+@c fsetlocking dup ok [no @mtasurace:stream @asulock, exclusive]
+@c isspace dup @mtslocale
+@c strlen dup ok
+@c malloc dup @ascuheap @acsmem
+@c fclose dup @ascuheap @asulock @aculock @acsmem @acsfd
+@c memcpy dup ok
+@c getline dup @ascuheap @acsmem [no @asucorrupt @aculock @acucorrupt, exclusive]
+@c strptime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c feof_unlocked dup ok
+@c free dup @ascuheap @acsmem
+@c ferror_unlocked dup dup ok
+@c time dup ok
+@c localtime_r dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c first_wday @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c memset dup ok
+@c mktime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c check_mday ok
+@c mktime dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+The @code{getdate_r} function is the reentrant counterpart of
+@code{getdate}. It does not use the global variable @code{getdate_err}
+to signal an error, but instead returns an error code. The same error
+codes as described in the @code{getdate_err} documentation above are
+used, with 0 meaning success.
+
+Moreover, @code{getdate_r} stores the broken-down time in the variable
+of type @code{struct tm} pointed to by the second argument, rather than
+in a static variable.
+
+This function is not defined in the Unix standard. Nevertheless it is
+available on some other Unix systems as well.
+
+The warning against using @code{getdate} in SUID-programs applies to
+@code{getdate_r} as well.
@end deftypefun
@node TZ Variable
@cindex time zone
You should not normally need to set @code{TZ}. If the system is
-configured properly, the default timezone will be correct. You might
-set @code{TZ} if you are using a computer over the network from a
-different timezone, and would like times reported to you in the timezone
-that local for you, rather than what is local for the computer.
+configured properly, the default time zone will be correct. You might
+set @code{TZ} if you are using a computer over a network from a
+different time zone, and would like times reported to you in the time
+zone local to you, rather than what is local to the computer.
-In POSIX.1 systems the value of the @code{TZ} variable can be of one of
-three formats. With the GNU C library, the most common format is the
+In POSIX.1 systems the value of the @code{TZ} variable can be in one of
+three formats. With @theglibc{}, the most common format is the
last one, which can specify a selection from a large database of time
zone information for many regions of the world. The first two formats
are used to describe the time zone information directly, which is both
@end smallexample
The @var{std} string specifies the name of the time zone. It must be
-three or more characters long and must not contain a leading colon or
-embedded digits, commas, or plus or minus signs. There is no space
+three or more characters long and must not contain a leading colon,
+embedded digits, commas, nor plus and minus signs. There is no space
character separating the time zone name from the @var{offset}, so these
restrictions are necessary to parse the specification correctly.
-The @var{offset} specifies the time value one must add to the local time
+The @var{offset} specifies the time value you must add to the local time
to get a Coordinated Universal Time value. It has syntax like
[@code{+}|@code{-}]@var{hh}[@code{:}@var{mm}[@code{:}@var{ss}]]. This
is positive if the local time zone is west of the Prime Meridian and
@code{24}, and the minute and seconds between @code{0} and @code{59}.
For example, here is how we would specify Eastern Standard Time, but
-without any daylight savings time alternative:
+without any Daylight Saving Time alternative:
@smallexample
EST+5
The initial @var{std} and @var{offset} specify the standard time zone, as
described above. The @var{dst} string and @var{offset} specify the name
-and offset for the corresponding daylight savings time time zone; if the
+and offset for the corresponding Daylight Saving Time zone; if the
@var{offset} is omitted, it defaults to one hour ahead of standard time.
-The remainder of the specification describes when daylight savings time is
-in effect. The @var{start} field is when daylight savings time goes into
+The remainder of the specification describes when Daylight Saving Time is
+in effect. The @var{start} field is when Daylight Saving Time goes into
effect and the @var{end} field is when the change is made back to standard
time. The following formats are recognized for these fields:
The @var{time} fields specify when, in the local time currently in
effect, the change to the other time occurs. If omitted, the default is
-@code{02:00:00}.
-
-For example, here is how one would specify the Eastern time zone in the
-United States, including the appropriate daylight saving time and its dates
-of applicability. The normal offset from GMT is 5 hours; since this is
+@code{02:00:00}. The hours part of the time fields can range from
+@minus{}167 through 167; this is an extension to POSIX.1, which allows
+only the range 0 through 24.
+
+Here are some example @code{TZ} values, including the appropriate
+Daylight Saving Time and its dates of applicability. In North
+American Eastern Standard Time (EST) and Eastern Daylight Time (EDT),
+the normal offset from UTC is 5 hours; since this is
west of the prime meridian, the sign is positive. Summer time begins on
-the first Sunday in April at 2:00am, and ends on the last Sunday in October
+March's second Sunday at 2:00am, and ends on November's first Sunday
at 2:00am.
@smallexample
-EST+5EDT,M4.1.0/M10.5.0
+EST+5EDT,M3.2.0/2,M11.1.0/2
+@end smallexample
+
+Israel Standard Time (IST) and Israel Daylight Time (IDT) are 2 hours
+ahead of the prime meridian in winter, springing forward an hour on
+March's fourth Thursday at 26:00 (i.e., 02:00 on the first Friday on or
+after March 23), and falling back on October's last Sunday at 02:00.
+
+@smallexample
+IST-2IDT,M3.4.4/26,M10.5.0
+@end smallexample
+
+Western Argentina Summer Time (WARST) is 3 hours behind the prime
+meridian all year. There is a dummy fall-back transition on December
+31 at 25:00 daylight saving time (i.e., 24:00 standard time,
+equivalent to January 1 at 00:00 standard time), and a simultaneous
+spring-forward transition on January 1 at 00:00 standard time, so
+daylight saving time is in effect all year and the initial @code{WART}
+is a placeholder.
+
+@smallexample
+WART4WARST,J1/0,J365/25
+@end smallexample
+
+Western Greenland Time (WGT) and Western Greenland Summer Time (WGST)
+are 3 hours behind UTC in the winter. Its clocks follow the European
+Union rules of springing forward by one hour on March's last Sunday at
+01:00 UTC (@minus{}02:00 local time) and falling back on October's
+last Sunday at 01:00 UTC (@minus{}01:00 local time).
+
+@smallexample
+WGT3WGST,M3.5.0/-2,M10.5.0/-1
@end smallexample
-The schedule of daylight savings time in any particular jurisdiction has
+The schedule of Daylight Saving Time in any particular jurisdiction has
changed over the years. To be strictly correct, the conversion of dates
and times in the past should be based on the schedule that was in effect
then. However, this format has no facilities to let you specify how the
:@var{characters}
@end smallexample
-Each operating system interprets this format differently; in the GNU C
-library, @var{characters} is the name of a file which describes the time
+Each operating system interprets this format differently; in
+@theglibc{}, @var{characters} is the name of a file which describes the time
zone.
@pindex /etc/localtime
@pindex localtime
If the @code{TZ} environment variable does not have a value, the
-operation chooses a time zone by default. In the GNU C library, the
+operation chooses a time zone by default. In @theglibc{}, the
default time zone is like the specification @samp{TZ=:/etc/localtime}
-(or @samp{TZ=:/usr/local/etc/localtime}, depending on how GNU C library
+(or @samp{TZ=:/usr/local/etc/localtime}, depending on how @theglibc{}
was configured; @pxref{Installation}). Other C libraries use their own
rule for choosing the default time zone, so there is little we can say
about them.
@cindex time zone database
-@pindex /share/lib/zoneinfo
+@pindex /usr/share/zoneinfo
@pindex zoneinfo
If @var{characters} begins with a slash, it is an absolute file name;
otherwise the library looks for the file
-@w{@file{/share/lib/zoneinfo/@var{characters}}}. The @file{zoneinfo}
+@w{@file{/usr/share/zoneinfo/@var{characters}}}. The @file{zoneinfo}
directory contains data files describing local time zones in many
different parts of the world. The names represent major cities, with
subdirectories for geographical areas; for example,
@file{America/New_York}, @file{Europe/London}, @file{Asia/Hong_Kong}.
These data files are installed by the system administrator, who also
sets @file{/etc/localtime} to point to the data file for the local time
-zone. The GNU C library comes with a large database of time zone
+zone. The files typically come from the @url{http://www.iana.org/time-zones,
+Time Zone Database} of time zone and daylight saving time
information for most regions of the world, which is maintained by a
community of volunteers and put in the public domain.
@node Time Zone Functions
@subsection Functions and Variables for Time Zones
-@comment time.h
-@comment POSIX.1
-@deftypevar char * tzname [2]
+@deftypevar {char *} tzname [2]
+@standards{POSIX.1, time.h}
The array @code{tzname} contains two strings, which are the standard
-names of the pair of time zones (standard and daylight
-savings) that the user has selected. @code{tzname[0]} is the name of
+names of the pair of time zones (standard and Daylight
+Saving) that the user has selected. @code{tzname[0]} is the name of
the standard time zone (for example, @code{"EST"}), and @code{tzname[1]}
-is the name for the time zone when daylight savings time is in use (for
+is the name for the time zone when Daylight Saving Time is in use (for
example, @code{"EDT"}). These correspond to the @var{std} and @var{dst}
-strings (respectively) from the @code{TZ} environment variable.
+strings (respectively) from the @code{TZ} environment variable. If
+Daylight Saving Time is never used, @code{tzname[1]} is the empty string.
The @code{tzname} array is initialized from the @code{TZ} environment
variable whenever @code{tzset}, @code{ctime}, @code{strftime},
-@code{mktime}, or @code{localtime} is called.
+@code{mktime}, or @code{localtime} is called. If multiple abbreviations
+have been used (e.g. @code{"EWT"} and @code{"EDT"} for U.S. Eastern War
+Time and Eastern Daylight Time), the array contains the most recent
+abbreviation.
+
+The @code{tzname} array is required for POSIX.1 compatibility, but in
+GNU programs it is better to use the @code{tm_zone} member of the
+broken-down time structure, since @code{tm_zone} reports the correct
+abbreviation even when it is not the latest one.
+
+Though the strings are declared as @code{char *} the user must refrain
+from modifying these strings. Modifying the strings will almost certainly
+lead to trouble.
+
@end deftypevar
-@comment time.h
-@comment POSIX.1
@deftypefun void tzset (void)
+@standards{POSIX.1, time.h}
+@safety{@prelim{}@mtsafe{@mtsenv{} @mtslocale{}}@asunsafe{@ascuheap{} @asulock{}}@acunsafe{@aculock{} @acsmem{} @acsfd{}}}
+@c tzset @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c libc_lock_lock dup @asulock @aculock
+@c tzset_internal dup @mtsenv @mtslocale @ascuheap @asulock @aculock @acsmem @acsfd
+@c libc_lock_unlock dup @aculock
The @code{tzset} function initializes the @code{tzname} variable from
the value of the @code{TZ} environment variable. It is not usually
necessary for your program to call this function, because it is called
@end deftypefun
The following variables are defined for compatibility with System V
-Unix. These variables are set by calling @code{tzset}.
+Unix. Like @code{tzname}, these variables are set by calling
+@code{tzset} or the other time conversion functions.
-@comment time.h
-@comment SVID
@deftypevar {long int} timezone
-This contains the difference between GMT and local standard time, in
-seconds. For example, in the U.S. Eastern time zone, the value is
-@code{5*60*60}.
+@standards{SVID, time.h}
+This contains the difference between UTC and the latest local standard
+time, in seconds west of UTC. For example, in the U.S. Eastern time
+zone, the value is @code{5*60*60}. Unlike the @code{tm_gmtoff} member
+of the broken-down time structure, this value is not adjusted for
+daylight saving, and its sign is reversed. In GNU programs it is better
+to use @code{tm_gmtoff}, since it contains the correct offset even when
+it is not the latest one.
@end deftypevar
-@comment time.h
-@comment SVID
@deftypevar int daylight
-This variable has a nonzero value if daylight savings time rules apply.
-A nonzero value does not necessarily mean that daylight savings time is
-now in effect; it means only that daylight savings time is sometimes in
+@standards{SVID, time.h}
+This variable has a nonzero value if Daylight Saving Time rules apply.
+A nonzero value does not necessarily mean that Daylight Saving Time is
+now in effect; it means only that Daylight Saving Time is sometimes in
effect.
@end deftypevar
@node Time Functions Example
@subsection Time Functions Example
-Here is an example program showing the use of some of the local time and
-calendar time functions.
+Here is an example program showing the use of some of the calendar time
+functions.
@smallexample
@include strftim.c.texi
@section Setting an Alarm
The @code{alarm} and @code{setitimer} functions provide a mechanism for a
-process to interrupt itself at some future time. They do this by setting a
+process to interrupt itself in the future. They do this by setting a
timer; when the timer expires, the process receives a signal.
@cindex setting an alarm
Each process has three independent interval timers available:
@itemize @bullet
-@item
-A real-time timer that counts clock time. This timer sends a
+@item
+A real-time timer that counts elapsed time. This timer sends a
@code{SIGALRM} signal to the process when it expires.
@cindex real-time timer
@cindex timer, real-time
-@item
-A virtual timer that counts CPU time used by the process. This timer
+@item
+A virtual timer that counts processor time used by the process. This timer
sends a @code{SIGVTALRM} signal to the process when it expires.
@cindex virtual timer
@cindex timer, virtual
-@item
-A profiling timer that counts both CPU time used by the process, and CPU
-time spent in system calls on behalf of the process. This timer sends a
-@code{SIGPROF} signal to the process when it expires.
+@item
+A profiling timer that counts both processor time used by the process,
+and processor time spent in system calls on behalf of the process. This
+timer sends a @code{SIGPROF} signal to the process when it expires.
@cindex profiling timer
@cindex timer, profiling
new value.
You should establish a handler for the appropriate alarm signal using
-@code{signal} or @code{sigaction} before issuing a call to @code{setitimer}
-or @code{alarm}. Otherwise, an unusual chain of events could cause the
-timer to expire before your program establishes the handler, and in that
-case it would be terminated, since that is the default action for the alarm
-signals. @xref{Signal Handling}.
+@code{signal} or @code{sigaction} before issuing a call to
+@code{setitimer} or @code{alarm}. Otherwise, an unusual chain of events
+could cause the timer to expire before your program establishes the
+handler. In this case it would be terminated, since termination is the
+default action for the alarm signals. @xref{Signal Handling}.
+
+To be able to use the alarm function to interrupt a system call which
+might block otherwise indefinitely it is important to @emph{not} set the
+@code{SA_RESTART} flag when registering the signal handler using
+@code{sigaction}. When not using @code{sigaction} things get even
+uglier: the @code{signal} function has fixed semantics with respect
+to restarts. The BSD semantics for this function is to set the flag.
+Therefore, if @code{sigaction} for whatever reason cannot be used, it is
+necessary to use @code{sysv_signal} and not @code{signal}.
The @code{setitimer} function is the primary means for setting an alarm.
This facility is declared in the header file @file{sys/time.h}. The
@pindex unistd.h
@pindex sys/time.h
-@comment sys/time.h
-@comment BSD
@deftp {Data Type} {struct itimerval}
+@standards{BSD, sys/time.h}
This structure is used to specify when a timer should expire. It contains
the following members:
@table @code
@item struct timeval it_interval
-This is the interval between successive timer interrupts. If zero, the
+This is the period between successive timer interrupts. If zero, the
alarm will only be sent once.
@item struct timeval it_value
-This is the interval to the first timer interrupt. If zero, the alarm is
-disabled.
+This is the period between now and the first timer interrupt. If zero,
+the alarm is disabled.
@end table
-The @code{struct timeval} data type is described in @ref{High-Resolution
-Calendar}.
+The @code{struct timeval} data type is described in @ref{Elapsed Time}.
@end deftp
-@comment sys/time.h
-@comment BSD
-@deftypefun int setitimer (int @var{which}, struct itimerval *@var{new}, struct itimerval *@var{old})
-The @code{setitimer} function sets the timer specified by @var{which}
+@deftypefun int setitimer (int @var{which}, const struct itimerval *@var{new}, struct itimerval *@var{old})
+@standards{BSD, sys/time.h}
+@safety{@prelim{}@mtsafe{@mtstimer{}}@assafe{}@acsafe{}}
+@c This function is marked with @mtstimer because the same set of timers
+@c is shared by all threads of a process, so calling it in one thread
+@c may interfere with timers set by another thread. This interference
+@c is not regarded as destructive, because the interface specification
+@c makes this overriding while returning the previous value the expected
+@c behavior, and the kernel will serialize concurrent calls so that the
+@c last one prevails, with each call getting the timer information from
+@c the timer installed by the previous call in that serialization.
+The @code{setitimer} function sets the timer specified by @var{which}
according to @var{new}. The @var{which} argument can have a value of
@code{ITIMER_REAL}, @code{ITIMER_VIRTUAL}, or @code{ITIMER_PROF}.
@table @code
@item EINVAL
-The timer interval was too large.
+The timer period is too large.
@end table
@end deftypefun
-@comment sys/time.h
-@comment BSD
@deftypefun int getitimer (int @var{which}, struct itimerval *@var{old})
+@standards{BSD, sys/time.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
The @code{getitimer} function stores information about the timer specified
by @var{which} in the structure pointed at by @var{old}.
The return value and error conditions are the same as for @code{setitimer}.
@end deftypefun
-@comment sys/time.h
-@comment BSD
-@table @code
+@vtable @code
@item ITIMER_REAL
-@findex ITIMER_REAL
+@standards{BSD, sys/time.h}
This constant can be used as the @var{which} argument to the
@code{setitimer} and @code{getitimer} functions to specify the real-time
timer.
-@comment sys/time.h
-@comment BSD
@item ITIMER_VIRTUAL
-@findex ITIMER_VIRTUAL
+@standards{BSD, sys/time.h}
This constant can be used as the @var{which} argument to the
@code{setitimer} and @code{getitimer} functions to specify the virtual
timer.
-@comment sys/time.h
-@comment BSD
@item ITIMER_PROF
-@findex ITIMER_PROF
+@standards{BSD, sys/time.h}
This constant can be used as the @var{which} argument to the
@code{setitimer} and @code{getitimer} functions to specify the profiling
timer.
-@end table
+@end vtable
-@comment unistd.h
-@comment POSIX.1
@deftypefun {unsigned int} alarm (unsigned int @var{seconds})
+@standards{POSIX.1, unistd.h}
+@safety{@prelim{}@mtsafe{@mtstimer{}}@assafe{}@acsafe{}}
+@c Wrapper for setitimer.
The @code{alarm} function sets the real-time timer to expire in
@var{seconds} seconds. If you want to cancel any existing alarm, you
can do this by calling @code{alarm} with a @var{seconds} argument of
zero.
The return value indicates how many seconds remain before the previous
-alarm would have been sent. If there is no previous alarm, @code{alarm}
+alarm would have been sent. If there was no previous alarm, @code{alarm}
returns zero.
@end deftypefun
@section Sleeping
The function @code{sleep} gives a simple way to make the program wait
-for short periods of time. If your program doesn't use signals (except
-to terminate), then you can expect @code{sleep} to wait reliably for
-the specified amount of time. Otherwise, @code{sleep} can return sooner
-if a signal arrives; if you want to wait for a given period regardless
-of signals, use @code{select} (@pxref{Waiting for I/O}) and don't
-specify any descriptors to wait for.
+for a short interval. If your program doesn't use signals (except to
+terminate), then you can expect @code{sleep} to wait reliably throughout
+the specified interval. Otherwise, @code{sleep} can return sooner if a
+signal arrives; if you want to wait for a given interval regardless of
+signals, use @code{select} (@pxref{Waiting for I/O}) and don't specify
+any descriptors to wait for.
@c !!! select can get EINTR; using SA_RESTART makes sleep win too.
-@comment unistd.h
-@comment POSIX.1
@deftypefun {unsigned int} sleep (unsigned int @var{seconds})
-The @code{sleep} function waits for @var{seconds} or until a signal
-is delivered, whichever happens first.
-
-If @code{sleep} function returns because the requested time has
-elapsed, it returns a value of zero. If it returns because of delivery
-of a signal, its return value is the remaining time in the sleep period.
+@standards{POSIX.1, unistd.h}
+@safety{@prelim{}@mtunsafe{@mtascusig{:SIGCHLD/linux}}@asunsafe{}@acunsafe{}}
+@c On Mach, it uses ports and calls time. On generic posix, it calls
+@c nanosleep. On Linux, it temporarily blocks SIGCHLD, which is MT- and
+@c AS-Unsafe, and in a way that makes it AC-Unsafe (C-unsafe, even!).
+The @code{sleep} function waits for @var{seconds} seconds or until a signal
+is delivered, whichever happens first.
+
+If @code{sleep} returns because the requested interval is over,
+it returns a value of zero. If it returns because of delivery of a
+signal, its return value is the remaining time in the sleep interval.
The @code{sleep} function is declared in @file{unistd.h}.
@end deftypefun
few signals happen to arrive in rapid succession by bad luck---there is
no limit on how much this could shorten or lengthen the wait.
-Instead, compute the time at which the program should stop waiting, and
-keep trying to wait until that time. This won't be off by more than a
-second. With just a little more work, you can use @code{select} and
-make the waiting period quite accurate. (Of course, heavy system load
-can cause unavoidable additional delays---unless the machine is
-dedicated to one application, there is no way you can avoid this.)
+Instead, compute the calendar time at which the program should stop
+waiting, and keep trying to wait until that calendar time. This won't
+be off by more than a second. With just a little more work, you can use
+@code{select} and make the waiting period quite accurate. (Of course,
+heavy system load can cause additional unavoidable delays---unless the
+machine is dedicated to one application, there is no way you can avoid
+this.)
On some systems, @code{sleep} can do strange things if your program uses
@code{SIGALRM} explicitly. Even if @code{SIGALRM} signals are being
whose handler requests an alarm or alters the handling of @code{SIGALRM},
this handler and @code{sleep} will interfere.
-On the GNU system, it is safe to use @code{sleep} and @code{SIGALRM} in
+On @gnusystems{}, it is safe to use @code{sleep} and @code{SIGALRM} in
the same program, because @code{sleep} does not work by means of
@code{SIGALRM}.
-@node Resource Usage
-@section Resource Usage
-
-@pindex sys/resource.h
-The function @code{getrusage} and the data type @code{struct rusage}
-are used for examining the usage figures of a process. They are declared
-in @file{sys/resource.h}.
-
-@comment sys/resource.h
-@comment BSD
-@deftypefun int getrusage (int @var{processes}, struct rusage *@var{rusage})
-This function reports the usage totals for processes specified by
-@var{processes}, storing the information in @code{*@var{rusage}}.
-
-In most systems, @var{processes} has only two valid values:
-
-@table @code
-@comment sys/resource.h
-@comment BSD
-@item RUSAGE_SELF
-Just the current process.
-
-@comment sys/resource.h
-@comment BSD
-@item RUSAGE_CHILDREN
-All child processes (direct and indirect) that have terminated already.
-@end table
-
-In the GNU system, you can also inquire about a particular child process
-by specifying its process ID.
-
-The return value of @code{getrusage} is zero for success, and @code{-1}
-for failure.
-
-@table @code
-@item EINVAL
-The argument @var{processes} is not valid.
-@end table
-@end deftypefun
-
-One way of getting usage figures for a particular child process is with
-the function @code{wait4}, which returns totals for a child when it
-terminates. @xref{BSD Wait Functions}.
-
-@comment sys/resource.h
-@comment BSD
-@deftp {Data Type} {struct rusage}
-This data type records a collection usage amounts for various sorts of
-resources. It has the following members, and possibly others:
-
-@table @code
-@item struct timeval ru_utime
-Time spent executing user instructions.
-
-@item struct timeval ru_stime
-Time spent in operating system code on behalf of @var{processes}.
-
-@item long int ru_maxrss
-The maximum resident set size used, in kilobytes. That is, the maximum
-number of kilobytes that @var{processes} used in real memory simultaneously.
-
-@item long int ru_ixrss
-An integral value expressed in kilobytes times ticks of execution, which
-indicates the amount of memory used by text that was shared with other
-processes.
-
-@item long int ru_idrss
-An integral value expressed the same way, which is the amount of
-unshared memory used in data.
-
-@item long int ru_isrss
-An integral value expressed the same way, which is the amount of
-unshared memory used in stack space.
-
-@item long int ru_minflt
-The number of page faults which were serviced without requiring any I/O.
-
-@item long int ru_majflt
-The number of page faults which were serviced by doing I/O.
+@deftypefun int nanosleep (const struct timespec *@var{requested_time}, struct timespec *@var{remaining})
+@standards{POSIX.1, time.h}
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+@c On Linux, it's a syscall. On Mach, it calls gettimeofday and uses
+@c ports.
+If resolution to seconds is not enough the @code{nanosleep} function can
+be used. As the name suggests the sleep interval can be specified in
+nanoseconds. The actual elapsed time of the sleep interval might be
+longer since the system rounds the elapsed time you request up to the
+next integer multiple of the actual resolution the system can deliver.
-@item long int ru_nswap
-The number of times @var{processes} was swapped entirely out of main memory.
+*@code{requested_time} is the elapsed time of the interval you want to
+sleep.
-@item long int ru_inblock
-The number of times the file system had to read from the disk on behalf
-of @var{processes}.
+The function returns as *@code{remaining} the elapsed time left in the
+interval for which you requested to sleep. If the interval completed
+without getting interrupted by a signal, this is zero.
-@item long int ru_oublock
-The number of times the file system had to write to the disk on behalf
-of @var{processes}.
+@code{struct timespec} is described in @xref{Elapsed Time}.
-@item long int ru_msgsnd
-Number of IPC messages sent.
-
-@item long ru_msgrcv
-Number of IPC messages received.
-
-@item long int ru_nsignals
-Number of signals received.
-
-@item long int ru_nvcsw
-The number of times @var{processes} voluntarily invoked a context switch
-(usually to wait for some service).
-
-@item long int ru_nivcsw
-The number of times an involuntary context switch took place (because
-the time slice expired, or another process of higher priority became
-runnable).
-@end table
-@end deftp
-
-An additional historical function for examining usage figures,
-@code{vtimes}, is supported but not documented here. It is declared in
-@file{sys/vtimes.h}.
-
-@node Limits on Resources
-@section Limiting Resource Usage
-@cindex resource limits
-@cindex limits on resource usage
-@cindex usage limits
-
-You can specify limits for the resource usage of a process. When the
-process tries to exceed a limit, it may get a signal, or the system call
-by which it tried to do so may fail, depending on the limit. Each
-process initially inherits its limit values from its parent, but it can
-subsequently change them.
-
-@pindex sys/resource.h
-The symbols in this section are defined in @file{sys/resource.h}.
-
-@comment sys/resource.h
-@comment BSD
-@deftypefun int getrlimit (int @var{resource}, struct rlimit *@var{rlp})
-Read the current value and the maximum value of resource @var{resource}
-and store them in @code{*@var{rlp}}.
-
-The return value is @code{0} on success and @code{-1} on failure. The
-only possible @code{errno} error condition is @code{EFAULT}.
-@end deftypefun
-
-@comment sys/resource.h
-@comment BSD
-@deftypefun int setrlimit (int @var{resource}, struct rlimit *@var{rlp})
-Store the current value and the maximum value of resource @var{resource}
-in @code{*@var{rlp}}.
-
-The return value is @code{0} on success and @code{-1} on failure. The
-following @code{errno} error condition is possible:
-
-@table @code
-@item EPERM
-You tried to change the maximum permissible limit value,
-but you don't have privileges to do so.
-@end table
-@end deftypefun
-
-@comment sys/resource.h
-@comment BSD
-@deftp {Data Type} {struct rlimit}
-This structure is used with @code{getrlimit} to receive limit values,
-and with @code{setrlimit} to specify limit values. It has two fields:
-
-@table @code
-@item rlim_cur
-The current value of the limit in question.
-This is also called the ``soft limit''.
-@cindex soft limit
-
-@item rlim_max
-The maximum permissible value of the limit in question. You cannot set
-the current value of the limit to a larger number than this maximum.
-Only the super user can change the maximum permissible value.
-This is also called the ``hard limit''.
-@cindex hard limit
-@end table
-
-In @code{getrlimit}, the structure is an output; it receives the current
-values. In @code{setrlimit}, it specifies the new values.
-@end deftp
-
-Here is a list of resources that you can specify a limit for.
-Those that are sizes are measured in bytes.
-
-@table @code
-@comment sys/resource.h
-@comment BSD
-@item RLIMIT_CPU
-@vindex RLIMIT_CPU
-The maximum amount of cpu time the process can use. If it runs for
-longer than this, it gets a signal: @code{SIGXCPU}. The value is
-measured in seconds. @xref{Operation Error Signals}.
-
-@comment sys/resource.h
-@comment BSD
-@item RLIMIT_FSIZE
-@vindex RLIMIT_FSIZE
-The maximum size of file the process can create. Trying to write a
-larger file causes a signal: @code{SIGXFSZ}. @xref{Operation Error
-Signals}.
-
-@comment sys/resource.h
-@comment BSD
-@item RLIMIT_DATA
-@vindex RLIMIT_DATA
-The maximum size of data memory for the process. If the process tries
-to allocate data memory beyond this amount, the allocation function
-fails.
-
-@comment sys/resource.h
-@comment BSD
-@item RLIMIT_STACK
-@vindex RLIMIT_STACK
-The maximum stack size for the process. If the process tries to extend
-its stack past this size, it gets a @code{SIGSEGV} signal.
-@xref{Program Error Signals}.
-
-@comment sys/resource.h
-@comment BSD
-@item RLIMIT_CORE
-@vindex RLIMIT_CORE
-The maximum size core file that this process can create. If the process
-terminates and would dump a core file larger than this maximum size,
-then no core file is created. So setting this limit to zero prevents
-core files from ever being created.
-
-@comment sys/resource.h
-@comment BSD
-@item RLIMIT_RSS
-@vindex RLIMIT_RSS
-The maximum amount of physical memory that this process should get.
-This parameter is a guide for the system's scheduler and memory
-allocator; the system may give the process more memory when there is a
-surplus.
-
-@comment sys/resource.h
-@comment BSD
-@item RLIMIT_MEMLOCK
-The maximum amount of memory that can be locked into physical memory (so
-it will never be paged out).
-
-@comment sys/resource.h
-@comment BSD
-@item RLIMIT_NPROC
-The maximum number of processes that can be created with the same user ID.
-If you have reached the limit for your user ID, @code{fork} will fail
-with @code{EAGAIN}. @xref{Creating a Process}.
-
-@comment sys/resource.h
-@comment BSD
-@item RLIMIT_NOFILE
-@vindex RLIMIT_NOFILE
-@itemx RLIMIT_OFILE
-@vindex RLIMIT_OFILE
-The maximum number of files that the process can open. If it tries to
-open more files than this, it gets error code @code{EMFILE}.
-@xref{Error Codes}. Not all systems support this limit; GNU does, and
-4.4 BSD does.
-
-@comment sys/resource.h
-@comment BSD
-@item RLIM_NLIMITS
-@vindex RLIM_NLIMITS
-The number of different resource limits. Any valid @var{resource}
-operand must be less than @code{RLIM_NLIMITS}.
-@end table
-
-@comment sys/resource.h
-@comment BSD
-@defvr Constant int RLIM_INFINITY
-This constant stands for a value of ``infinity'' when supplied as
-the limit value in @code{setrlimit}.
-@end defvr
-
-@c ??? Someone want to finish these?
-Two historical functions for setting resource limits, @code{ulimit} and
-@code{vlimit}, are not documented here. The latter is declared in
-@file{sys/vlimit.h} and comes from BSD.
-
-@node Priority
-@section Process Priority
-@cindex process priority
-@cindex priority of a process
-
-@pindex sys/resource.h
-When several processes try to run, their respective priorities determine
-what share of the CPU each process gets. This section describes how you
-can read and set the priority of a process. All these functions and
-macros are declared in @file{sys/resource.h}.
-
-The range of valid priority values depends on the operating system, but
-typically it runs from @code{-20} to @code{20}. A lower priority value
-means the process runs more often. These constants describe the range of
-priority values:
-
-@table @code
-@comment sys/resource.h
-@comment BSD
-@item PRIO_MIN
-@vindex PRIO_MIN
-The smallest valid priority value.
-
-@comment sys/resource.h
-@comment BSD
-@item PRIO_MAX
-@vindex PRIO_MAX
-The smallest valid priority value.
-@end table
-
-@comment sys/resource.h
-@comment BSD
-@deftypefun int getpriority (int @var{class}, int @var{id})
-Read the priority of a class of processes; @var{class} and @var{id}
-specify which ones (see below). If the processes specified do not all
-have the same priority, this returns the smallest value that any of them
-has.
-
-The return value is the priority value on success, and @code{-1} on
-failure. The following @code{errno} error condition are possible for
-this function:
-
-@table @code
-@item ESRCH
-The combination of @var{class} and @var{id} does not match any existing
-process.
-
-@item EINVAL
-The value of @var{class} is not valid.
-@end table
-
-When the return value is @code{-1}, it could indicate failure, or it
-could be the priority value. The only way to make certain is to set
-@code{errno = 0} before calling @code{getpriority}, then use @code{errno
-!= 0} afterward as the criterion for failure.
-@end deftypefun
-
-@comment sys/resource.h
-@comment BSD
-@deftypefun int setpriority (int @var{class}, int @var{id}, int @var{priority})
-Set the priority of a class of processes to @var{priority}; @var{class}
-and @var{id} specify which ones (see below).
-
-The return value is @code{0} on success and @code{-1} on failure. The
-following @code{errno} error condition are defined for this function:
+If the function returns because the interval is over the return value is
+zero. If the function returns @math{-1} the global variable @code{errno}
+is set to the following values:
@table @code
-@item ESRCH
-The combination of @var{class} and @var{id} does not match any existing
-process.
+@item EINTR
+The call was interrupted because a signal was delivered to the thread.
+If the @var{remaining} parameter is not the null pointer the structure
+pointed to by @var{remaining} is updated to contain the remaining
+elapsed time.
@item EINVAL
-The value of @var{class} is not valid.
-
-@item EPERM
-You tried to set the priority of some other user's process, and you
-don't have privileges for that.
-
-@item EACCES
-You tried to lower the priority of a process, and you don't have
-privileges for that.
-@end table
-@end deftypefun
-
-The arguments @var{class} and @var{id} together specify a set of
-processes you are interested in. These are the possible values for
-@var{class}:
-
-@table @code
-@comment sys/resource.h
-@comment BSD
-@item PRIO_PROCESS
-@vindex PRIO_PROCESS
-Read or set the priority of one process. The argument @var{id} is a
-process ID.
-
-@comment sys/resource.h
-@comment BSD
-@item PRIO_PGRP
-@vindex PRIO_PGRP
-Read or set the priority of one process group. The argument @var{id} is
-a process group ID.
-
-@comment sys/resource.h
-@comment BSD
-@item PRIO_USER
-@vindex PRIO_USER
-Read or set the priority of one user's processes. The argument @var{id}
-is a user ID.
+The nanosecond value in the @var{requested_time} parameter contains an
+illegal value. Either the value is negative or greater than or equal to
+1000 million.
@end table
-If the argument @var{id} is 0, it stands for the current process,
-current process group, or the current user, according to @var{class}.
-
-@c ??? I don't know where we should say this comes from.
-@comment Unix
-@comment dunno.h
-@deftypefun int nice (int @var{increment})
-Increment the priority of the current process by @var{increment}.
-The return value is the same as for @code{setpriority}.
-
-Here is an equivalent definition for @code{nice}:
+This function is a cancellation point in multi-threaded programs. This
+is a problem if the thread allocates some resources (like memory, file
+descriptors, semaphores or whatever) at the time @code{nanosleep} is
+called. If the thread gets canceled these resources stay allocated
+until the program ends. To avoid this calls to @code{nanosleep} should
+be protected using cancellation handlers.
+@c ref pthread_cleanup_push / pthread_cleanup_pop
-@smallexample
-int
-nice (int increment)
-@{
- int old = getpriority (PRIO_PROCESS, 0);
- return setpriority (PRIO_PROCESS, 0, old + increment);
-@}
-@end smallexample
+The @code{nanosleep} function is declared in @file{time.h}.
@end deftypefun
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