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Finding Today's Date

Problem

You need to find the year, month, and day values for today's date.

Solution

Use current-seconds, and seconds->date to get a date structure type representing today.

(let* ((seconds (current-seconds))
       (today (seconds->date seconds)))
  (values
   (date-day today)
   (date-month today)
   (date-year today)))

Discussion

Using the date library from Mzlib, you can easily convert a date structure to a string.

(require (lib "date.ss"))

(let* ((seconds (current-seconds))
       (today (seconds->date seconds)))
  (date->string today))

which will return something like "Wednesday, April 21st, 2004". The returned string contains the time of day only if the second, optional, argument to date->string is #t, so, using =(date->string today #t)= above would return: "Wednesday, April 21st, 2004 12:54:20pm".

SRFI 19 provides equivalent funciontallity, and much more. Thus if you would want to use the time.ss library from the srfi collection, to get today's date you could do:

(require (lib "date.ss"))

(let* ((seconds (current-seconds))
       (today (seconds->date seconds)))
  (date->string today))

which will return "Wed Apr 21 13:01:01-0500 2004".

Note that the format returned by these different date->string procedures, the former from the Mzlib collection, the later from SRFI-19, differs. The number of arguments these procedures receive also differs, the one form SRFI-19 supports localization, the other one not, etc.

To change the format of the returning string using Mzlib, you need to use (date-display-format [format-symbol]), with one of the supported format symbols: ='american, 'chinese, 'german, 'indian, 'irish, 'iso-8601, 'rfc2822=, or 'julian. The initial format is 'american. For instance,

(require (lib "date.ss"))

(let* ((seconds (current-seconds))
       (today (seconds->date seconds)))
  (date-display-format 'iso-8601)
  (date->string today))

which would return "2004-04-21".

To change the format using SRFI-19 accordingly, you have to instruct date->string using its second, optional, argument.

(require (lib "19.ss" "srfi")) ;; or (require (lib "19.ss" "srfi" "time"))

(let ((today (current-date)))
  (date->string today "~1"))

See Also

If you are using DrScheme, then use Help Desk to access the MzScheme manual, and the documentation for SRFI-19.

Comments here

-- FranciscoSolsona - 28 Apr 2004