Info Catalog elisp: User Identification elisp: System Interface elisp: Time Zone Rules

elisp: Time of Day

 
 38.5 Time of Day
 ================
 
 This section explains how to determine the current time and time zone.
 
    Most of these functions represent time as a list of four integers
 ‘(SEC-HIGH SEC-LOW MICROSEC PICOSEC)’.  This represents the number of
 seconds from the “epoch” (January 1, 1970 at 00:00 UTC), using the
 formula: HIGH * 2**16 + LOW + MICRO * 10**−6 + PICO * 10**−12.  The
 return value of ‘current-time’ represents time using this form, as do
 the timestamps in the return values of other functions such as
 ‘file-attributes’ (Definition of file-attributes).  In some
 cases, functions may return two- or three-element lists, with omitted
 MICROSEC and PICOSEC components defaulting to zero.
 
    Function arguments, e.g., the TIME argument to ‘current-time-string’,
 accept a more-general “time value” format, which can be a list of
 integers as above, or a single number for seconds since the epoch, or
 ‘nil’ for the current time.  You can convert a time value into a
 human-readable string using ‘current-time-string’ and
 ‘format-time-string’, into a list of integers using ‘seconds-to-time’,
 and into other forms using ‘decode-time’ and ‘float-time’.  These
 functions are described in the following sections.
 
  -- Function: current-time-string &optional time zone
      This function returns the current time and date as a human-readable
      string.  The format does not vary for the initial part of the
      string, which contains the day of week, month, day of month, and
      time of day in that order: the number of characters used for these
      fields is always the same, so you can reliably use ‘substring’ to
      extract them.  You should count characters from the beginning of
      the string rather than from the end, as the year might not have
      exactly four digits, and additional information may some day be
      added at the end.
 
      The argument TIME, if given, specifies a time to format, instead of
      the current time.  The optional argument ZONE defaults to the
      current time zone rule.  Time Zone Rules.
 
           (current-time-string)
                ⇒ "Wed Oct 14 22:21:05 1987"
 
  -- Function: current-time
      This function returns the current time, represented as a list of
      four integers ‘(SEC-HIGH SEC-LOW MICROSEC PICOSEC)’.  These
      integers have trailing zeros on systems that return time with lower
      resolutions.  On all current machines PICOSEC is a multiple of
      1000, but this may change as higher-resolution clocks become
      available.
 
  -- Function: float-time &optional time
      This function returns the current time as a floating-point number
      of seconds since the epoch.  The optional argument TIME, if given,
      specifies a time to convert instead of the current time.
 
      _Warning_: Since the result is floating point, it may not be exact.
      Do not use this function if precise time stamps are required.
 
      ‘time-to-seconds’ is an alias for this function.
 
  -- Function: seconds-to-time time
      This function converts a time value to list-of-integer form.  For
      example, if TIME is a number, ‘(time-to-seconds (seconds-to-time
      TIME))’ equals the number unless overflow or rounding errors occur.
 

Info Catalog elisp: User Identification elisp: System Interface elisp: Time Zone Rules