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2711 lines
95 KiB
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2711 lines
95 KiB
Plaintext
@node Date and Time, Non-Local Exits, Arithmetic, Top
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@c %MENU% Functions for getting the date and time and formatting them nicely
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@chapter Date and Time
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This chapter describes functions for manipulating dates and times,
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including functions for determining what the current time is and
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conversion between different time representations.
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The time functions fall into three main categories:
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@itemize @bullet
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@item
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Functions for measuring elapsed CPU time are discussed in @ref{Processor
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Time}.
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@item
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Functions for measuring absolute clock or calendar time are discussed in
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@ref{Calendar Time}.
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@item
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Functions for setting alarms and timers are discussed in @ref{Setting
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an Alarm}.
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@end itemize
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@menu
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* Processor Time:: Measures processor time used by a program.
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* Calendar Time:: Manipulation of ``real'' dates and times.
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* Precision Time:: Manipulation and monitoring of high accuracy
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time.
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* Setting an Alarm:: Sending a signal after a specified time.
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* Sleeping:: Waiting for a period of time.
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* Resource Usage:: Measuring various resources used.
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* Limits on Resources:: Specifying limits on resource usage.
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* Priority:: Reading or setting process run priority.
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@end menu
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@node Processor Time
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@section Processor Time
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If you're trying to optimize your program or measure its efficiency, it's
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very useful to be able to know how much @dfn{processor time} or @dfn{CPU
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time} it has used at any given point. Processor time is different from
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actual wall clock time because it doesn't include any time spent waiting
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for I/O or when some other process is running. Processor time is
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represented by the data type @code{clock_t}, and is given as a number of
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@dfn{clock ticks} relative to an arbitrary base time marking the beginning
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of a single program invocation.
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@cindex CPU time
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@cindex processor time
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@cindex clock ticks
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@cindex ticks, clock
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@cindex time, elapsed CPU
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@menu
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* Basic CPU Time:: The @code{clock} function.
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* Detailed CPU Time:: The @code{times} function.
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@end menu
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@node Basic CPU Time
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@subsection Basic CPU Time Inquiry
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To get the elapsed CPU time used by a process, you can use the
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@code{clock} function. This facility is declared in the header file
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@file{time.h}.
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@pindex time.h
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In typical usage, you call the @code{clock} function at the beginning and
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end of the interval you want to time, subtract the values, and then divide
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by @code{CLOCKS_PER_SEC} (the number of clock ticks per second), like this:
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@smallexample
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@group
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#include <time.h>
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clock_t start, end;
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double elapsed;
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start = clock();
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@dots{} /* @r{Do the work.} */
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end = clock();
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elapsed = ((double) (end - start)) / CLOCKS_PER_SEC;
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@end group
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@end smallexample
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Different computers and operating systems vary wildly in how they keep
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track of processor time. It's common for the internal processor clock
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to have a resolution somewhere between hundredth and millionth of a
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second.
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In the GNU system, @code{clock_t} is equivalent to @code{long int} and
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@code{CLOCKS_PER_SEC} is an integer value. But in other systems, both
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@code{clock_t} and the type of the macro @code{CLOCKS_PER_SEC} can be
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either integer or floating-point types. Casting processor time values
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to @code{double}, as in the example above, makes sure that operations
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such as arithmetic and printing work properly and consistently no matter
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what the underlying representation is.
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Note that the clock can wrap around. On a 32bit system with
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@code{CLOCKS_PER_SEC} set to one million a wrap around happens after
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around 36 minutes.
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@comment time.h
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@comment ISO
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@deftypevr Macro int CLOCKS_PER_SEC
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The value of this macro is the number of clock ticks per second measured
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by the @code{clock} function. POSIX requires that this value is one
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million independend of the actual resolution.
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@end deftypevr
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@comment time.h
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@comment POSIX.1
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@deftypevr Macro int CLK_TCK
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This is an obsolete name for @code{CLOCKS_PER_SEC}.
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@end deftypevr
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@comment time.h
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@comment ISO
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@deftp {Data Type} clock_t
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This is the type of the value returned by the @code{clock} function.
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Values of type @code{clock_t} are in units of clock ticks.
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@end deftp
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@comment time.h
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@comment ISO
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@deftypefun clock_t clock (void)
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This function returns the elapsed processor time. The base time is
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arbitrary but doesn't change within a single process. If the processor
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time is not available or cannot be represented, @code{clock} returns the
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value @code{(clock_t)(-1)}.
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@end deftypefun
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@node Detailed CPU Time
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@subsection Detailed Elapsed CPU Time Inquiry
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The @code{times} function returns more detailed information about
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elapsed processor time in a @w{@code{struct tms}} object. You should
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include the header file @file{sys/times.h} to use this facility.
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@pindex sys/times.h
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@comment sys/times.h
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@comment POSIX.1
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@deftp {Data Type} {struct tms}
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The @code{tms} structure is used to return information about process
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times. It contains at least the following members:
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@table @code
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@item clock_t tms_utime
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This is the CPU time used in executing the instructions of the calling
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process.
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@item clock_t tms_stime
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This is the CPU time used by the system on behalf of the calling process.
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@item clock_t tms_cutime
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This is the sum of the @code{tms_utime} values and the @code{tms_cutime}
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values of all terminated child processes of the calling process, whose
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status has been reported to the parent process by @code{wait} or
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@code{waitpid}; see @ref{Process Completion}. In other words, it
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represents the total CPU time used in executing the instructions of all
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the terminated child processes of the calling process, excluding child
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processes which have not yet been reported by @code{wait} or
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@code{waitpid}.
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@item clock_t tms_cstime
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This is similar to @code{tms_cutime}, but represents the total CPU time
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used by the system on behalf of all the terminated child processes of the
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calling process.
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@end table
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All of the times are given in clock ticks. These are absolute values; in a
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newly created process, they are all zero. @xref{Creating a Process}.
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@end deftp
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@comment sys/times.h
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@comment POSIX.1
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@deftypefun clock_t times (struct tms *@var{buffer})
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The @code{times} function stores the processor time information for
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the calling process in @var{buffer}.
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The return value is the same as the value of @code{clock()}: the elapsed
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real time relative to an arbitrary base. The base is a constant within a
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particular process, and typically represents the time since system
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start-up. A value of @code{(clock_t)(-1)} is returned to indicate failure.
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@end deftypefun
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@strong{Portability Note:} The @code{clock} function described in
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@ref{Basic CPU Time}, is specified by the @w{ISO C} standard. The
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@code{times} function is a feature of POSIX.1. In the GNU system, the
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value returned by the @code{clock} function is equivalent to the sum of
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the @code{tms_utime} and @code{tms_stime} fields returned by
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@code{times}.
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@node Calendar Time
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@section Calendar Time
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This section describes facilities for keeping track of dates and times
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according to the Gregorian calendar.
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@cindex Gregorian calendar
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@cindex time, calendar
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@cindex date and time
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There are three representations for date and time information:
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@itemize @bullet
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@item
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@dfn{Calendar time} (the @code{time_t} data type) is a compact
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representation, typically giving the number of seconds elapsed since
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some implementation-specific base time.
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@cindex calendar time
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@item
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There is also a @dfn{high-resolution time} representation (the @code{struct
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timeval} data type) that includes fractions of a second. Use this time
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representation instead of ordinary calendar time when you need greater
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precision.
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@cindex high-resolution time
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@item
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@dfn{Local time} or @dfn{broken-down time} (the @code{struct
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tm} data type) represents the date and time as a set of components
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specifying the year, month, and so on, for a specific time zone.
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This time representation is usually used in conjunction with formatting
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date and time values.
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@cindex local time
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@cindex broken-down time
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@end itemize
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@menu
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* Simple Calendar Time:: Facilities for manipulating calendar time.
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* High-Resolution Calendar:: A time representation with greater precision.
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* Broken-down Time:: Facilities for manipulating local time.
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* Formatting Date and Time:: Converting times to strings.
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* Parsing Date and Time:: Convert textual time and date information back
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into broken-down time values.
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* TZ Variable:: How users specify the time zone.
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* Time Zone Functions:: Functions to examine or specify the time zone.
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* Time Functions Example:: An example program showing use of some of
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the time functions.
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@end menu
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@node Simple Calendar Time
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@subsection Simple Calendar Time
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This section describes the @code{time_t} data type for representing
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calendar time, and the functions which operate on calendar time objects.
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These facilities are declared in the header file @file{time.h}.
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@pindex time.h
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@cindex epoch
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@comment time.h
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@comment ISO
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@deftp {Data Type} time_t
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This is the data type used to represent calendar time.
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When interpreted as an absolute time
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value, it represents the number of seconds elapsed since 00:00:00 on
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January 1, 1970, Coordinated Universal Time. (This date is sometimes
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referred to as the @dfn{epoch}.) POSIX requires that this count
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ignore leap seconds, but on some hosts this count includes leap seconds
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if you set @code{TZ} to certain values (@pxref{TZ Variable}).
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In the GNU C library, @code{time_t} is equivalent to @code{long int}.
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In other systems, @code{time_t} might be either an integer or
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floating-point type.
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@end deftp
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@comment time.h
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@comment ISO
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@deftypefun double difftime (time_t @var{time1}, time_t @var{time0})
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The @code{difftime} function returns the number of seconds elapsed
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between time @var{time1} and time @var{time0}, as a value of type
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@code{double}. The difference ignores leap seconds unless leap
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second support is enabled.
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In the GNU system, you can simply subtract @code{time_t} values. But on
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other systems, the @code{time_t} data type might use some other encoding
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where subtraction doesn't work directly.
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@end deftypefun
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@comment time.h
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@comment ISO
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@deftypefun time_t time (time_t *@var{result})
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The @code{time} function returns the current time as a value of type
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@code{time_t}. If the argument @var{result} is not a null pointer, the
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time value is also stored in @code{*@var{result}}. If the calendar
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time is not available, the value @w{@code{(time_t)(-1)}} is returned.
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@end deftypefun
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@node High-Resolution Calendar
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@subsection High-Resolution Calendar
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The @code{time_t} data type used to represent calendar times has a
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resolution of only one second. Some applications need more precision.
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So, the GNU C library also contains functions which are capable of
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representing calendar times to a higher resolution than one second. The
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functions and the associated data types described in this section are
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declared in @file{sys/time.h}.
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@pindex sys/time.h
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@comment sys/time.h
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@comment BSD
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@deftp {Data Type} {struct timeval}
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The @code{struct timeval} structure represents a calendar time. It
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has the following members:
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@table @code
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@item long int tv_sec
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This represents the number of seconds since the epoch. It is equivalent
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to a normal @code{time_t} value.
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@item long int tv_usec
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This is the fractional second value, represented as the number of
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microseconds.
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Some times struct timeval values are used for time intervals. Then the
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@code{tv_sec} member is the number of seconds in the interval, and
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@code{tv_usec} is the number of additional microseconds.
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@end table
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@end deftp
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@comment sys/time.h
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@comment BSD
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@deftp {Data Type} {struct timezone}
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The @code{struct timezone} structure is used to hold minimal information
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about the local time zone. It has the following members:
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@table @code
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@item int tz_minuteswest
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This is the number of minutes west of UTC.
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@item int tz_dsttime
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If nonzero, daylight saving time applies during some part of the year.
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@end table
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The @code{struct timezone} type is obsolete and should never be used.
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Instead, use the facilities described in @ref{Time Zone Functions}.
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@end deftp
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It is often necessary to subtract two values of type @w{@code{struct
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timeval}}. Here is the best way to do this. It works even on some
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peculiar operating systems where the @code{tv_sec} member has an
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unsigned type.
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@smallexample
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/* @r{Subtract the `struct timeval' values X and Y,}
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@r{storing the result in RESULT.}
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@r{Return 1 if the difference is negative, otherwise 0.} */
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int
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timeval_subtract (result, x, y)
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struct timeval *result, *x, *y;
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@{
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/* @r{Perform the carry for the later subtraction by updating @var{y}.} */
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if (x->tv_usec < y->tv_usec) @{
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int nsec = (y->tv_usec - x->tv_usec) / 1000000 + 1;
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y->tv_usec -= 1000000 * nsec;
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y->tv_sec += nsec;
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@}
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if (x->tv_usec - y->tv_usec > 1000000) @{
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int nsec = (x->tv_usec - y->tv_usec) / 1000000;
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y->tv_usec += 1000000 * nsec;
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y->tv_sec -= nsec;
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@}
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/* @r{Compute the time remaining to wait.}
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@r{@code{tv_usec} is certainly positive.} */
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result->tv_sec = x->tv_sec - y->tv_sec;
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result->tv_usec = x->tv_usec - y->tv_usec;
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/* @r{Return 1 if result is negative.} */
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return x->tv_sec < y->tv_sec;
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@}
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@end smallexample
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@comment sys/time.h
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@comment BSD
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@deftypefun int gettimeofday (struct timeval *@var{tp}, struct timezone *@var{tzp})
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The @code{gettimeofday} function returns the current date and time in the
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@code{struct timeval} structure indicated by @var{tp}. Information about the
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time zone is returned in the structure pointed at @var{tzp}. If the @var{tzp}
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argument is a null pointer, time zone information is ignored.
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The return value is @code{0} on success and @code{-1} on failure. The
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following @code{errno} error condition is defined for this function:
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@table @code
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@item ENOSYS
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The operating system does not support getting time zone information, and
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@var{tzp} is not a null pointer. The GNU operating system does not
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support using @w{@code{struct timezone}} to represent time zone
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information; that is an obsolete feature of 4.3 BSD.
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Instead, use the facilities described in @ref{Time Zone Functions}.
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@end table
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@end deftypefun
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@comment sys/time.h
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@comment BSD
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@deftypefun int settimeofday (const struct timeval *@var{tp}, const struct timezone *@var{tzp})
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The @code{settimeofday} function sets the current date and time
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according to the arguments. As for @code{gettimeofday}, time zone
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information is ignored if @var{tzp} is a null pointer.
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You must be a privileged user in order to use @code{settimeofday}.
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The return value is @code{0} on success and @code{-1} on failure. The
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following @code{errno} error conditions are defined for this function:
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@table @code
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@item EPERM
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This process cannot set the time because it is not privileged.
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@item ENOSYS
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The operating system does not support setting time zone information, and
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@var{tzp} is not a null pointer.
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@end table
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@end deftypefun
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@comment sys/time.h
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@comment BSD
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@deftypefun int adjtime (const struct timeval *@var{delta}, struct timeval *@var{olddelta})
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This function speeds up or slows down the system clock in order to make
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gradual adjustments in the current time. This ensures that the time
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reported by the system clock is always monotonically increasing, which
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might not happen if you simply set the current time.
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The @var{delta} argument specifies a relative adjustment to be made to
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the current time. If negative, the system clock is slowed down for a
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while until it has lost this much time. If positive, the system clock
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is speeded up for a while.
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If the @var{olddelta} argument is not a null pointer, the @code{adjtime}
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function returns information about any previous time adjustment that
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has not yet completed.
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This function is typically used to synchronize the clocks of computers
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in a local network. You must be a privileged user to use it.
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The return value is @code{0} on success and @code{-1} on failure. The
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following @code{errno} error condition is defined for this function:
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@table @code
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@item EPERM
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You do not have privilege to set the time.
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@end table
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@end deftypefun
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@strong{Portability Note:} The @code{gettimeofday}, @code{settimeofday},
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and @code{adjtime} functions are derived from BSD.
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@node Broken-down Time
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@subsection Broken-down Time
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@cindex broken-down time
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@cindex calendar time and broken-down time
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Calendar time is represented as a number of seconds. This is convenient
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for calculation, but has no resemblance to the way people normally
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represent dates and times. By contrast, @dfn{broken-down time} is a binary
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representation separated into year, month, day, and so on. Broken down
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time values are not useful for calculations, but they are useful for
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printing human readable time.
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A broken-down time value is always relative to a choice of local time
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zone, and it also indicates which time zone was used.
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The symbols in this section are declared in the header file @file{time.h}.
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@comment time.h
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@comment ISO
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@deftp {Data Type} {struct tm}
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This is the data type used to represent a broken-down time. The structure
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contains at least the following members, which can appear in any order:
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@table @code
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@item int tm_sec
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This is the number of seconds after the minute, normally in the range
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@code{0} through @code{59}. (The actual upper limit is @code{60}, to allow
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for leap seconds if leap second support is available.)
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@cindex leap second
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@item int tm_min
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This is the number of minutes after the hour, in the range @code{0} through
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@code{59}.
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@item int tm_hour
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This is the number of hours past midnight, in the range @code{0} through
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@code{23}.
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@item int tm_mday
|
|
This is the day of the month, in the range @code{1} through @code{31}.
|
|
|
|
@item int tm_mon
|
|
This is the number of months since January, in the range @code{0} through
|
|
@code{11}.
|
|
|
|
@item int tm_year
|
|
This is the number of years since @code{1900}.
|
|
|
|
@item int tm_wday
|
|
This is the number of 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} through
|
|
@code{365}.
|
|
|
|
@item int tm_isdst
|
|
@cindex Daylight Saving Time
|
|
@cindex summer time
|
|
This is a flag that indicates whether Daylight Saving Time is (or was, or
|
|
will be) in effect at the time described. The value is positive if
|
|
Daylight Saving Time is in effect, zero if it is not, and negative if the
|
|
information is not available.
|
|
|
|
@item long int tm_gmtoff
|
|
This field describes the time zone that was used to compute this
|
|
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. 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 ISO
|
|
@deftypefun {struct tm *} localtime (const time_t *@var{time})
|
|
The @code{localtime} function converts the calendar time pointed to by
|
|
@var{time} to broken-down time representation, expressed relative to the
|
|
user's specified time zone.
|
|
|
|
The return value is a pointer to a static broken-down time structure, which
|
|
might be overwritten by subsequent calls to @code{ctime}, @code{gmtime},
|
|
or @code{localtime}. (But no other library function overwrites the contents
|
|
of this object.)
|
|
|
|
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} has one other effect: it sets the variable
|
|
@code{tzname} with information about the current time zone. @xref{Time
|
|
Zone Functions}.
|
|
@end deftypefun
|
|
|
|
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 varient of this function.
|
|
|
|
@comment time.h
|
|
@comment POSIX.1c
|
|
@deftypefun {struct tm *} localtime_r (const time_t *@var{time}, struct tm *@var{resultp})
|
|
The @code{localtime_r} function works just like the @code{localtime}
|
|
function. It takes a pointer to a variable containing the calendar 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
|
|
|
|
|
|
@comment time.h
|
|
@comment ISO
|
|
@deftypefun {struct tm *} gmtime (const time_t *@var{time})
|
|
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.
|
|
|
|
Recall that calendar times are @emph{always} expressed in coordinated
|
|
universal time.
|
|
@end deftypefun
|
|
|
|
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}.
|
|
|
|
@comment time.h
|
|
@comment POSIX.1c
|
|
@deftypefun {struct tm *} gmtime_r (const time_t *@var{time}, struct tm *@var{resultp})
|
|
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
|
|
|
|
|
|
@comment time.h
|
|
@comment ISO
|
|
@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.
|
|
|
|
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
|
|
calendar time; it's permissible for these components to have
|
|
unnormalized values outside of 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}).
|
|
|
|
If the specified broken-down time cannot be represented as a calendar 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}.
|
|
@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}.
|
|
@pindex time.h
|
|
|
|
@comment time.h
|
|
@comment ISO
|
|
@deftypefun {char *} asctime (const struct tm *@var{brokentime})
|
|
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"
|
|
@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
|
|
|
|
@comment time.h
|
|
@comment POSIX.1c
|
|
@deftypefun {char *} asctime_r (const struct tm *@var{brokentime}, char *@var{buffer})
|
|
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 at least room
|
|
for 16 bytes.
|
|
|
|
If no error occurred the function returns a pointer to the string the
|
|
result was written into, i.e., it returns @var{buffer}. Otherwise
|
|
return @code{NULL}.
|
|
@end deftypefun
|
|
|
|
|
|
@comment time.h
|
|
@comment ISO
|
|
@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
|
|
|
|
@smallexample
|
|
asctime (localtime (@var{time}))
|
|
@end smallexample
|
|
|
|
@code{ctime} sets the variable @code{tzname}, because @code{localtime}
|
|
does so. @xref{Time Zone Functions}.
|
|
@end deftypefun
|
|
|
|
@comment time.h
|
|
@comment POSIX.1c
|
|
@deftypefun {char *} ctime_r (const time_t *@var{time}, char *@var{buffer})
|
|
This function is similar to @code{ctime}, only that it 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
|
|
return @code{NULL}.
|
|
@end deftypefun
|
|
|
|
|
|
@comment time.h
|
|
@comment ISO
|
|
@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}).
|
|
|
|
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 is 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 are POSIX.2 extensions, are:
|
|
|
|
@table @code
|
|
@item E
|
|
Use the locale's alternate 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
|
|
Use the locale's alternate numeric symbols for numbers. This modifier
|
|
applies only to numeric format specifiers.
|
|
@end table
|
|
|
|
If the format supports the modifier but no alternate 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.
|
|
|
|
@item %B
|
|
The full month name according to the current locale.
|
|
|
|
@item %c
|
|
The preferred date and 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.
|
|
|
|
This format is a POSIX.2 extension.
|
|
|
|
@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 is a POSIX.2 extension.
|
|
|
|
@item %e
|
|
The day of the month like with @code{%d}, but padded with blank (range
|
|
@code{ 1} through @code{31}).
|
|
|
|
This format is a POSIX.2 extension.
|
|
|
|
@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 is a @w{ISO C 9X} extension.
|
|
|
|
@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 is a GNU extension.
|
|
|
|
@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 is 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 is a POSIX.2 extension.
|
|
|
|
@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 blank (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 blank (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 is a POSIX.2 extension.
|
|
|
|
@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}.
|
|
|
|
@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}.
|
|
|
|
This format is a GNU extension.
|
|
|
|
@item %r
|
|
The complete time using the AM/PM format of the current locale.
|
|
|
|
This format is a POSIX.2 extension.
|
|
|
|
@item %R
|
|
The hour and minute in decimal numbers using the format @code{%H:%M}.
|
|
|
|
This format is 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 is a POSIX.2 extension.
|
|
|
|
@item %T
|
|
The time using decimal numbers using the format @code{%H:%M:%S}.
|
|
|
|
This format is a POSIX.2 extension.
|
|
|
|
@item %u
|
|
The day of the week as a decimal number (range @code{1} through
|
|
@code{7}), Monday being @code{1}.
|
|
|
|
This format is a POSIX.2 extension.
|
|
|
|
@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 is a POSIX.2 extension.
|
|
|
|
@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, but without the
|
|
time.
|
|
|
|
@item %X
|
|
The preferred time representation for the current locale, but with no date.
|
|
|
|
@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.
|
|
|
|
@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.
|
|
|
|
@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 is a GNU extension.
|
|
|
|
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 content of the array
|
|
@var{s} is indetermined. 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
|
|
|
|
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.
|
|
|
|
According to POSIX.1 every call to @code{strftime} implies a call to
|
|
@code{tzset}. So the contents of the environment variable @code{TZ}
|
|
is examined before any output is produced.
|
|
|
|
For an example of @code{strftime}, see @ref{Time Functions Example}.
|
|
@end deftypefun
|
|
|
|
@node Parsing Date and Time
|
|
@subsection Convert textual time and date information back
|
|
|
|
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 lead to variety of more or less successful implementations with
|
|
different interfaces over the years. Then the Unix standard got
|
|
extended by two functions: @code{strptime} and @code{getdate}. Both
|
|
have kind of strange interfaces but at least they are widely available.
|
|
|
|
@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
|
|
|
|
@node Low-Level Time String Parsing
|
|
@subsubsection Interpret string according to given format
|
|
|
|
The first function is a rather low-level interface. It is nevertheless
|
|
frequently used in user programs since it is better known. Its
|
|
implementation and the interface though is heavily influenced by the
|
|
@code{getdate} function which is defined and implemented in terms of
|
|
calls to @code{strptime}.
|
|
|
|
@comment time.h
|
|
@comment XPG4
|
|
@deftypefun {char *} strptime (const char *@var{s}, const char *@var{fmt}, struct tm *@var{tp})
|
|
The @code{strptime} function parses the input string @var{s} according
|
|
to the format string @var{fmt} and stores the found values in the
|
|
structure @var{tp}.
|
|
|
|
The input string can be retrieved in any way. It does not matter
|
|
whether it was generated by a @code{strftime} call or made up directly
|
|
by a program. It is also not necessary that the content is in any
|
|
human-recognizable format. I.e., it is OK if a date is written like
|
|
@code{"02:1999:9"} which is not understandable without context. As long
|
|
the format string @var{fmt} matches the format of the input string
|
|
everything goes.
|
|
|
|
The format string consists of the same components as the format string
|
|
for 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 formats which @code{strftime} handled differently do the
|
|
same work in @code{strptime} since differences like case of the output
|
|
do not matter. For symmetry reasons 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
|
|
@itemx %A
|
|
The weekday name according to the current locale, in abbreviated form or
|
|
the full name.
|
|
|
|
@item %b
|
|
@itemx %B
|
|
@itemx %h
|
|
The month name according to the current locale, in abbreviated form or
|
|
the full name.
|
|
|
|
@item %c
|
|
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 makes sometimes sense to use this format since in
|
|
some cultures it is required to specify years relative to periods
|
|
instead of using the Gregorian years.
|
|
|
|
@item %d
|
|
@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 the locale's alternative numeric symbols are used.
|
|
|
|
Leading zeroes are permitted but not required.
|
|
|
|
@item %D
|
|
Equivalent to the use of @code{%m/%d/%y} in this place.
|
|
|
|
@item %F
|
|
Equivalent to the use of @code{%Y-%m-%d} which is the @w{ISO 8601} date
|
|
format.
|
|
|
|
This is a GNU extension following an @w{ISO C 9X} 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:} This is not really implemented currently. 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:} This is not really implemented currently. 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
|
|
@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 are used.
|
|
|
|
@item %I
|
|
@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 are used.
|
|
|
|
@item %j
|
|
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{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 are used.
|
|
|
|
@item %M
|
|
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 are used.
|
|
|
|
@item %n
|
|
@itemx %t
|
|
Matches any white space.
|
|
|
|
@item %p
|
|
@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 seconds as a decimal number (range @code{0} through @code{61}).
|
|
|
|
Leading zeroes are permitted but not required.
|
|
|
|
Please note the nonsense with @code{61} being allowed. This is what the
|
|
Unix specification says. They followed the stupid decision once made to
|
|
allow double leap seconds. These do not exist but the myth persists.
|
|
|
|
@item %OS
|
|
Same as @code{%S} but using the locale's alternative numeric symbols are used.
|
|
|
|
@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:} This is not really implemented currently. 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 (range @code{0}
|
|
through @code{53}).
|
|
|
|
Leading zeroes are permitted but not required.
|
|
|
|
@item %OU
|
|
Same as @code{%U} but using the locale's alternative numeric symbols are used.
|
|
|
|
@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:} This is not really implemented currently. 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 (range @code{0} through
|
|
@code{6}), Sunday being @code{0}.
|
|
|
|
Leading zeroes are permitted but not required.
|
|
|
|
@emph{Note:} This is not really implemented currently. 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 are used.
|
|
|
|
@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:} This is not really implemented currently. 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 are used.
|
|
|
|
@item %x
|
|
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 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 without a century as a decimal number (range @code{0} through
|
|
@code{99}).
|
|
|
|
Leading zeroes are permitted but not required.
|
|
|
|
Please note that it is at least 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, using the Gregorian calendar.
|
|
|
|
@item %EY
|
|
The full alternative year representation.
|
|
|
|
@item %z
|
|
Equivalent to the use of @code{%a, %d %b %Y %H:%M:%S %z} in this place.
|
|
This is the full @w{ISO 8601} date and time format.
|
|
|
|
@item %Z
|
|
The timezone name.
|
|
|
|
@emph{Note:} This is not really implemented currently. The format is
|
|
recognized, input is consumed but no field in @var{tm} is set.
|
|
|
|
@item %%
|
|
A literal @samp{%} character.
|
|
@end table
|
|
|
|
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 white space characters in the input string.
|
|
|
|
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 return value of the function is a pointer to the first character not
|
|
processed in this function call. In case the input string contains more
|
|
characters than required by the format string the return value points
|
|
right after the last consumed input character. In case the whole input
|
|
string is consumed the return value points to the NUL byte at the end of
|
|
the string. If @code{strptime} fails to match all of the format string
|
|
and therefore an error occurred the function returns @code{NULL}.
|
|
@end deftypefun
|
|
|
|
The specification of the function in the XPG standard is rather vague.
|
|
It leaves out a few important pieces of information. Most important it
|
|
does not specify what happens to those elements of @var{tm} which are
|
|
not directly initialized by the different formats. Various
|
|
implementations on different Unix systems vary here.
|
|
|
|
The GNU libc 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 one
|
|
has to prepare the structure passed in as the @var{tm}. Normally this
|
|
will mean that all values are initialized to zero. Alternatively one
|
|
can use all fields to values like @code{INT_MAX} which allows 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 one wants to find out whether a
|
|
certain field in @var{tm} was initialized by the function call.
|
|
|
|
@item
|
|
One can construct a @code{struct tm} value in several @code{strptime}
|
|
calls in a row. A useful application of this is for example the parsing
|
|
of two separate strings, one containing the date information, the other
|
|
the time information. By parsing both one after the other without
|
|
clearing the structure in between one can construct a complete
|
|
broken-down time.
|
|
@end itemize
|
|
|
|
The following example shows a function which parses a string which is
|
|
supposed to contain 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 user-friendlier way to parse times and dates
|
|
|
|
The Unix standard defines another function to parse date strings. The
|
|
interface is, mildly said, weird. But if this function fits into the
|
|
application to be written it is just fine. It is a problem when using
|
|
this function in multi-threaded programs or in libraries since it
|
|
returns a pointer to a static variable, uses a global variable, and a
|
|
global state (an environment variable).
|
|
|
|
@comment time.h
|
|
@comment Unix98
|
|
@defvar getdate_err
|
|
This variable of type @code{int} will contain the error code of the last
|
|
unsuccessful call of the @code{getdate} function. 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 no 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 string is invalid for a template which would match otherwise.
|
|
This includes error like February 31st, or return values which can be
|
|
represented using @code{time_t}.
|
|
@end table
|
|
@end defvar
|
|
|
|
@comment time.h
|
|
@comment Unix98
|
|
@deftypefun {struct tm *} getdate (const char *@var{string})
|
|
The interface of the @code{getdate} function 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 passed to the user in a statically
|
|
allocated variable.
|
|
|
|
The details about how the string is processed is hidden from the user.
|
|
In fact, it can be outside the control of the program. Which formats
|
|
are recognized is controlled by the file named by the environment
|
|
variable @code{DATEMSK}. The content of the named 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 which were not initialized through the format string get
|
|
assigned the values of the time the @code{getdate} function is called.
|
|
|
|
The format elements recognized by @code{getdate} are the same as for
|
|
@code{strptime}. See above for an explanation. There are only a few
|
|
extension 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 in the timezone matched, not in 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) uses for
|
|
countries other than the USA will fail. So far we have found no good
|
|
solution for this.
|
|
|
|
@item
|
|
If only the weekday is specified the selected day depends on the current
|
|
date. If the current weekday is greater or equal to the @code{tm_wday}
|
|
value this weeks day is selected. Otherwise next weeks day.
|
|
|
|
@item
|
|
A similar heuristic is used if only the month is given, not the year.
|
|
For value corresponding to the current or a later month the current year
|
|
s used. Otherwise the next year. The first day of the month is assumed
|
|
if it is not explicitly specified.
|
|
|
|
@item
|
|
The current hour, minute, and second is used if the appropriate value is
|
|
not set through the format.
|
|
|
|
@item
|
|
If no date is given the date for the next day is used if the time is
|
|
smaller than the current time. Otherwise it is the same day.
|
|
@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 one 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 get the
|
|
following results for the given input.
|
|
|
|
@multitable {xxxxxxxxxxxx} {xxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx}
|
|
@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 in the variable pointed to by the return value is only valid
|
|
until the next @code{getdate} call which makes this function unusable in
|
|
multi-threaded applications.
|
|
|
|
The @code{errno} variable is @emph{not} changed. Error conditions are
|
|
signalled using 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 one 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
|
|
|
|
@comment time.h
|
|
@comment GNU
|
|
@deftypefun int getdate_r (const char *@var{string}, struct tm *@var{tp})
|
|
The @code{getdate_r} function is the reentrant counterpart of
|
|
@code{getdate}. It does not use the global variable @code{getdate_err}
|
|
to signal the error but instead the return value now is this error code.
|
|
The same error codes as described in the @code{getdate_err}
|
|
documentation above are used.
|
|
|
|
@code{getdate_r} also does not store the broken-down time in a static
|
|
variable. Instead it takes an second argument which must be a pointer
|
|
to a variable of type @code{struct tm} where the broken-down can be
|
|
stored.
|
|
|
|
This function is not defined in the Unix standard. Nevertheless it is
|
|
available on some other Unix systems as well.
|
|
|
|
As for @code{getdate} the warning for using this function in
|
|
SUID-programs applies to @code{getdate_r} as well.
|
|
@end deftypefun
|
|
|
|
@node TZ Variable
|
|
@subsection Specifying the Time Zone with @code{TZ}
|
|
|
|
In POSIX systems, a user can specify the time zone by means of the
|
|
@code{TZ} environment variable. For information about how to set
|
|
environment variables, see @ref{Environment Variables}. The functions
|
|
for accessing the time zone are declared in @file{time.h}.
|
|
@pindex time.h
|
|
@cindex time zone
|
|
|
|
You should not normally need to set @code{TZ}. If the system is
|
|
configured properly, the default time zone will be correct. You might
|
|
set @code{TZ} if you are using a computer over the network from a
|
|
different time zone, and would like times reported to you in the time zone
|
|
that local for you, rather than what is local for 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
|
|
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
|
|
more cumbersome and less precise. But the POSIX.1 standard only
|
|
specifies the details of the first two formats, so it is good to be
|
|
familiar with them in case you come across a POSIX.1 system that doesn't
|
|
support a time zone information database.
|
|
|
|
The first format is used when there is no Daylight Saving Time (or
|
|
summer time) in the local time zone:
|
|
|
|
@smallexample
|
|
@r{@var{std} @var{offset}}
|
|
@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
|
|
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
|
|
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
|
|
negative if it is east. The hour must be between @code{0} and
|
|
@code{23}, 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 saving time alternative:
|
|
|
|
@smallexample
|
|
EST+5
|
|
@end smallexample
|
|
|
|
The second format is used when there is Daylight Saving Time:
|
|
|
|
@smallexample
|
|
@r{@var{std} @var{offset} @var{dst} [@var{offset}]@code{,}@var{start}[@code{/}@var{time}]@code{,}@var{end}[@code{/}@var{time}]}
|
|
@end smallexample
|
|
|
|
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 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 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:
|
|
|
|
@table @code
|
|
@item J@var{n}
|
|
This specifies the Julian day, with @var{n} between @code{1} and @code{365}.
|
|
February 29 is never counted, even in leap years.
|
|
|
|
@item @var{n}
|
|
This specifies the Julian day, with @var{n} between @code{0} and @code{365}.
|
|
February 29 is counted in leap years.
|
|
|
|
@item M@var{m}.@var{w}.@var{d}
|
|
This specifies day @var{d} of week @var{w} of month @var{m}. The day
|
|
@var{d} must be between @code{0} (Sunday) and @code{6}. The week
|
|
@var{w} must be between @code{1} and @code{5}; week @code{1} is the
|
|
first week in which day @var{d} occurs, and week @code{5} specifies the
|
|
@emph{last} @var{d} day in the month. The month @var{m} should be
|
|
between @code{1} and @code{12}.
|
|
@end table
|
|
|
|
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 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
|
|
at 2:00am.
|
|
|
|
@smallexample
|
|
EST+5EDT,M4.1.0/2,M10.5.0/2
|
|
@end smallexample
|
|
|
|
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
|
|
schedule has changed from year to year. The most you can do is specify
|
|
one particular schedule---usually the present day schedule---and this is
|
|
used to convert any date, no matter when. For precise time zone
|
|
specifications, it is best to use the time zone information database
|
|
(see below).
|
|
|
|
The third format looks like this:
|
|
|
|
@smallexample
|
|
:@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
|
|
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
|
|
default time zone is like the specification @samp{TZ=:/etc/localtime}
|
|
(or @samp{TZ=:/usr/local/etc/localtime}, depending on how GNU C library
|
|
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 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}
|
|
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
|
|
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]
|
|
The array @code{tzname} contains two strings, which are the standard
|
|
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 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. 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. 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 stay away
|
|
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)
|
|
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
|
|
automatically when you use the other time conversion functions that
|
|
depend on the time zone.
|
|
@end deftypefun
|
|
|
|
The following variables are defined for compatibility with System V
|
|
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 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
|
|
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.
|
|
|
|
@smallexample
|
|
@include strftim.c.texi
|
|
@end smallexample
|
|
|
|
It produces output like this:
|
|
|
|
@smallexample
|
|
Wed Jul 31 13:02:36 1991
|
|
Today is Wednesday, July 31.
|
|
The time is 01:02 PM.
|
|
@end smallexample
|
|
|
|
|
|
@node Precision Time
|
|
@section Precision Time
|
|
|
|
@cindex time, high precision
|
|
@pindex sys/timex.h
|
|
The @code{net_gettime} and @code{ntp_adjtime} functions provide an
|
|
interface to monitor and manipulate high precision time. These
|
|
functions are declared in @file{sys/timex.h}.
|
|
|
|
@tindex struct ntptimeval
|
|
@deftp {Data Type} {struct ntptimeval}
|
|
This structure is used to monitor kernel time. It contains the
|
|
following members:
|
|
@table @code
|
|
@item struct timeval time
|
|
This is the current time. The @code{struct timeval} data type is
|
|
described in @ref{High-Resolution Calendar}.
|
|
|
|
@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
|
|
local clock against the true time.
|
|
@end table
|
|
@end deftp
|
|
|
|
@comment sys/timex,h
|
|
@comment GNU
|
|
@deftypefun int ntp_gettime (struct ntptimeval *@var{tptr})
|
|
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 a @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:
|
|
|
|
@table @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 table
|
|
@end deftypefun
|
|
|
|
@tindex struct timex
|
|
@deftp {Data Type} {struct timex}
|
|
This structure is used to control and monitor kernel time in a greater
|
|
level of detail. 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 local clock from the true
|
|
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 time
|
|
and the local 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 valiable 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 and can't be changed.
|
|
|
|
@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 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 local clock. The value is expressed in scaled PPM and it denotes
|
|
the difference in frequency between the local 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 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 numer 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 of calibrations where the stability
|
|
exceeded the threshold.
|
|
@end table
|
|
@end deftp
|
|
|
|
@comment sys/timex.h
|
|
@comment GNU
|
|
@deftypefun int ntp_adjtime (struct timex *@var{tptr})
|
|
The @code{ntp_adjtime} function sets the structure specified by
|
|
@var{tptr} to current values. In addition, values passed in @var{tptr}
|
|
can be used to replace existing settings. To do this the @code{modes}
|
|
element of the @code{struct timex} must be set appropriately. Setting
|
|
it to zero selects reading the current state.
|
|
|
|
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 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. Another reason could be that the specified new values
|
|
are not allowed.
|
|
@end table
|
|
|
|
For more details see RFC1305 (Network Time Protocol, Version 3) and
|
|
related documents.
|
|
@end deftypefun
|
|
|
|
|
|
@node Setting an Alarm
|
|
@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
|
|
timer; when the timer expires, the process receives a signal.
|
|
|
|
@cindex setting an alarm
|
|
@cindex interval timer, setting
|
|
@cindex alarms, setting
|
|
@cindex timers, setting
|
|
Each process has three independent interval timers available:
|
|
|
|
@itemize @bullet
|
|
@item
|
|
A real-time timer that counts clock 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
|
|
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.
|
|
@cindex profiling timer
|
|
@cindex timer, profiling
|
|
|
|
This timer is useful for profiling in interpreters. The interval timer
|
|
mechanism does not have the fine granularity necessary for profiling
|
|
native code.
|
|
@c @xref{profil} !!!
|
|
@end itemize
|
|
|
|
You can only have one timer of each kind set at any given time. If you
|
|
set a timer that has not yet expired, that timer is simply reset to the
|
|
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}.
|
|
|
|
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
|
|
@code{alarm} function, declared in @file{unistd.h}, provides a somewhat
|
|
simpler interface for setting the real-time timer.
|
|
@pindex unistd.h
|
|
@pindex sys/time.h
|
|
|
|
@comment sys/time.h
|
|
@comment BSD
|
|
@deftp {Data Type} {struct itimerval}
|
|
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
|
|
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.
|
|
@end table
|
|
|
|
The @code{struct timeval} data type is described in @ref{High-Resolution
|
|
Calendar}.
|
|
@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}
|
|
according to @var{new}. The @var{which} argument can have a value of
|
|
@code{ITIMER_REAL}, @code{ITIMER_VIRTUAL}, or @code{ITIMER_PROF}.
|
|
|
|
If @var{old} is not a null pointer, @code{setitimer} returns information
|
|
about any previous unexpired timer of the same kind in the structure it
|
|
points to.
|
|
|
|
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 EINVAL
|
|
The timer interval was too large.
|
|
@end table
|
|
@end deftypefun
|
|
|
|
@comment sys/time.h
|
|
@comment BSD
|
|
@deftypefun int getitimer (int @var{which}, struct itimerval *@var{old})
|
|
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
|
|
@item ITIMER_REAL
|
|
@findex ITIMER_REAL
|
|
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
|
|
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
|
|
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
|
|
|
|
@comment unistd.h
|
|
@comment POSIX.1
|
|
@deftypefun {unsigned int} alarm (unsigned int @var{seconds})
|
|
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}
|
|
returns zero.
|
|
@end deftypefun
|
|
|
|
The @code{alarm} function could be defined in terms of @code{setitimer}
|
|
like this:
|
|
|
|
@smallexample
|
|
unsigned int
|
|
alarm (unsigned int seconds)
|
|
@{
|
|
struct itimerval old, new;
|
|
new.it_interval.tv_usec = 0;
|
|
new.it_interval.tv_sec = 0;
|
|
new.it_value.tv_usec = 0;
|
|
new.it_value.tv_sec = (long int) seconds;
|
|
if (setitimer (ITIMER_REAL, &new, &old) < 0)
|
|
return 0;
|
|
else
|
|
return old.it_value.tv_sec;
|
|
@}
|
|
@end smallexample
|
|
|
|
There is an example showing the use of the @code{alarm} function in
|
|
@ref{Handler Returns}.
|
|
|
|
If you simply want your process to wait for a given number of seconds,
|
|
you should use the @code{sleep} function. @xref{Sleeping}.
|
|
|
|
You shouldn't count on the signal arriving precisely when the timer
|
|
expires. In a multiprocessing environment there is typically some
|
|
amount of delay involved.
|
|
|
|
@strong{Portability Note:} The @code{setitimer} and @code{getitimer}
|
|
functions are derived from BSD Unix, while the @code{alarm} function is
|
|
specified by the POSIX.1 standard. @code{setitimer} is more powerful than
|
|
@code{alarm}, but @code{alarm} is more widely used.
|
|
|
|
@node Sleeping
|
|
@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.
|
|
@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.
|
|
|
|
The @code{sleep} function is declared in @file{unistd.h}.
|
|
@end deftypefun
|
|
|
|
Resist the temptation to implement a sleep for a fixed amount of time by
|
|
using the return value of @code{sleep}, when nonzero, to call
|
|
@code{sleep} again. This will work with a certain amount of accuracy as
|
|
long as signals arrive infrequently. But each signal can cause the
|
|
eventual wakeup time to be off by an additional second or so. Suppose a
|
|
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.)
|
|
|
|
On some systems, @code{sleep} can do strange things if your program uses
|
|
@code{SIGALRM} explicitly. Even if @code{SIGALRM} signals are being
|
|
ignored or blocked when @code{sleep} is called, @code{sleep} might
|
|
return prematurely on delivery of a @code{SIGALRM} signal. If you have
|
|
established a handler for @code{SIGALRM} signals and a @code{SIGALRM}
|
|
signal is delivered while the process is sleeping, the action taken
|
|
might be just to cause @code{sleep} to return instead of invoking your
|
|
handler. And, if @code{sleep} is interrupted by delivery of a signal
|
|
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
|
|
the same program, because @code{sleep} does not work by means of
|
|
@code{SIGALRM}.
|
|
|
|
@comment time.h
|
|
@comment POSIX.1
|
|
@deftypefun int nanosleep (const struct timespec *@var{requested_time}, struct timespec *@var{remaining})
|
|
If the resolution of seconds is not enough the @code{nanosleep} function
|
|
can be used. As the name suggests the sleeping period can be specified
|
|
in nanoseconds. The actual period of waiting time might be longer since
|
|
the requested time in the @var{requested_time} parameter is rounded up
|
|
to the next integer multiple of the actual resolution of the system.
|
|
|
|
If the function returns because the time has elapsed the return value is
|
|
zero. If the function return @math{-1} the global variable @var{errno}
|
|
is set to the following values:
|
|
|
|
@table @code
|
|
@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 time.
|
|
|
|
@item EINVAL
|
|
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
|
|
|
|
This function is a cancelation 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 cancelation handlers.
|
|
@c ref pthread_cleanup_push / pthread_cleanup_pop
|
|
|
|
The @code{nanosleep} function is declared in @file{time.h}.
|
|
@end deftypefun
|
|
|
|
@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.
|
|
|
|
@item long int ru_nswap
|
|
The number of times @var{processes} was swapped entirely out of main memory.
|
|
|
|
@item long int ru_inblock
|
|
The number of times the file system had to read from the disk on behalf
|
|
of @var{processes}.
|
|
|
|
@item long int ru_oublock
|
|
The number of times the file system had to write to the disk on behalf
|
|
of @var{processes}.
|
|
|
|
@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}.
|
|
|
|
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
|
|
32 bits system this function is in fact @code{getrlimit64}. I.e., the
|
|
LFS interface transparently replaces the old interface.
|
|
@end deftypefun
|
|
|
|
@comment sys/resource.h
|
|
@comment Unix98
|
|
@deftypefun int getrlimit64 (int @var{resource}, struct rlimit64 *@var{rlp})
|
|
This function is similar to the @code{getrlimit} but its second
|
|
parameter is a pointer to a variable of type @code{struct rlimit64}
|
|
which allows this function to read values which wouldn't fit in the
|
|
member of a @code{struct rlimit}.
|
|
|
|
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a 32
|
|
bits machine this function is available under the name @code{getrlimit}
|
|
and so transparently replaces the old interface.
|
|
@end deftypefun
|
|
|
|
@comment sys/resource.h
|
|
@comment BSD
|
|
@deftypefun int setrlimit (int @var{resource}, const 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
|
|
|
|
When the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a
|
|
32 bits system this function is in fact @code{setrlimit64}. I.e., the
|
|
LFS interface transparently replaces the old interface.
|
|
@end deftypefun
|
|
|
|
@comment sys/resource.h
|
|
@comment Unix98
|
|
@deftypefun int setrlimit64 (int @var{resource}, const struct rlimit64 *@var{rlp})
|
|
This function is similar to the @code{setrlimit} but its second
|
|
parameter is a pointer to a variable of type @code{struct rlimit64}
|
|
which allows this function to set values which wouldn't fit in the
|
|
member of a @code{struct rlimit}.
|
|
|
|
If the sources are compiled with @code{_FILE_OFFSET_BITS == 64} on a 32
|
|
bits machine this function is available under the name @code{setrlimit}
|
|
and so transparently replaces the old interface.
|
|
@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_t rlim_cur
|
|
The current value of the limit in question.
|
|
This is also called the ``soft limit''.
|
|
@cindex soft limit
|
|
|
|
@item rlim_t 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
|
|
|
|
For the LFS functions a similar type is defined in @file{sys/resource.h}.
|
|
|
|
@comment sys/resource.h
|
|
@comment Unix98
|
|
@deftp {Data Type} {struct rlimit64}
|
|
This structure is used with @code{getrlimit64} to receive limit values,
|
|
and with @code{setrlimit64} to specify limit values. It has two fields:
|
|
|
|
@table @code
|
|
@item rlim64_t rlim_cur
|
|
The current value of the limit in question.
|
|
This is also called the ``soft limit''.
|
|
|
|
@item rlim64_t 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''.
|
|
@end table
|
|
|
|
In @code{getrlimit64}, the structure is an output; it receives the current
|
|
values. In @code{setrlimit64}, 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
|
|
@deftypevr Constant int RLIM_INFINITY
|
|
This constant stands for a value of ``infinity'' when supplied as
|
|
the limit value in @code{setrlimit}.
|
|
@end deftypevr
|
|
|
|
@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 largest 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:
|
|
|
|
@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.
|
|
|
|
@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.
|
|
@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}:
|
|
|
|
@smallexample
|
|
int
|
|
nice (int increment)
|
|
@{
|
|
int old = getpriority (PRIO_PROCESS, 0);
|
|
return setpriority (PRIO_PROCESS, 0, old + increment);
|
|
@}
|
|
@end smallexample
|
|
@end deftypefun
|