Delphi Basics : FormatDateTime command

Delphi Basics
FormatDateTime Function	Rich formatting of a TDateTime variable into a string	SysUtils unit

1	function FormatDateTime ( const Formatting : string; DateTime : TDateTime ) : string;
2	function FormatDateTime ( const Formatting : string; DateTime : TDateTime; const FormatSettings : TFormatSettings ) : string;

Description

The FormatDateTime function provides rich formatting of a TDateTime value DateTime into a string. Formatting is defined by the Formatting string.

The Formatting string can comprise a mix of ordinary characters (that are passed unchanged to the result string), and data formatting characters. This formatting is best explained by the example code.

The following (non-Asian) formatting character strings can be used in the Formatting string:

y	= Year last 2 digits
yy	= Year last 2 digits
yyyy	= Year as 4 digits
m	= Month number no-leading 0
mm	= Month number as 2 digits
mmm	= Month using ShortDayNames (Jan)
mmmm	= Month using LongDayNames (January)
d	= Day number no-leading 0
dd	= Day number as 2 digits
ddd	= Day using ShortDayNames (Sun)
dddd	= Day using LongDayNames (Sunday)
ddddd	= Day in ShortDateFormat
dddddd	= Day in LongDateFormat

c	= Use ShortDateFormat + LongTimeFormat
h	= Hour number no-leading 0
hh	= Hour number as 2 digits
n	= Minute number no-leading 0
nn	= Minute number as 2 digits
s	= Second number no-leading 0
ss	= Second number as 2 digits
z	= Milli-sec number no-leading 0s
zzz	= Milli-sec number as 3 digits
t	= Use ShortTimeFormat
tt	= Use LongTimeFormat

am/pm	= Use after h : gives 12 hours + am/pm
a/p	= Use after h : gives 12 hours + a/p
ampm	= As a/p but TimeAMString,TimePMString
/	= Substituted by DateSeparator value
:	= Substituted by TimeSeparator value

Important : if you want to see characters such as dd in the formatted output, placing them in " marks will stop them being interpreted as date or time elements.

In addition to this formatting, various of the above options are affected by the following variables, withe their default values :

DateSeparator	= /
TimeSeparator	= :
ShortDateFormat	= dd/mm/yyyy
LongDateFormat	= dd mmm yyyy
TimeAMString	= AM
TimePMString	= PM
ShortTimeFormat	= hh:mm
LongTimeFormat	= hh:mm:ss
ShortMonthNames	= Jan Feb ...
LongMonthNames	= January, February ...
ShortDayNames	= Sun, Mon ...
LongDayNames	= Sunday, Monday ...
TwoDigitYearCenturyWindow	= 50

Version 2 of this function is for use within threads. You furnish the FormatSettings record before invoking the call. It takes a local copy of global formatting variables that make the routine thread safe.

Related commands

DateSeparator		The character used to separate display date fields
DateTimeToStr		Converts TDateTime date and time values to a string
DateTimeToString		Rich formatting of a TDateTime variable into a string
LongDateFormat		Long version of the date to string format
LongDayNames		An array of days of the week names, starting 1 = Sunday
LongMonthNames		An array of days of the month names, starting 1 = January
LongTimeFormat		Long version of the time to string format
ShortDateFormat		Compact version of the date to string format
ShortDayNames		An array of days of the week names, starting 1 = Sunday
ShortMonthNames		An array of days of the month names, starting 1 = Jan
ShortTimeFormat		Short version of the time to string format
StrToDateTime		Converts a date+time string into a TDateTime value
TimeAMString		Determines AM value in DateTimeToString procedure
TimePMString		Determines PM value in DateTimeToString procedure
TimeSeparator		The character used to separate display time fields
TwoDigitYearCenturyWindow		Sets the century threshold for 2 digit year string conversions

Example code : Showing all of the date field formatting data types

var
  myDate : TDateTime;

begin
  // Set up our TDateTime variable with a full date and time :
  // 09/02/2000 at 01:02:03.004  (.004 milli-seconds)
  myDate := EncodeDateTime(2000, 2, 9, 1, 2, 3, 4);

  // Date only - numeric values with no leading zeroes (except year)
  ShowMessage('              d/m/y = '+
              FormatDateTime('d/m/y', myDate));

  // Date only - numeric values with leading zeroes
  ShowMessage('           dd/mm/yy = '+
              FormatDateTime('dd/mm/yy', myDate));

  // Use short names for the day, month, and add freeform text ('of')
  ShowMessage('  ddd d of mmm yyyy = '+
              FormatDateTime('ddd d of mmm yyyy', myDate));

  // Use long names for the day and month
  ShowMessage('dddd d of mmmm yyyy = '+
              FormatDateTime('dddd d of mmmm yyyy', myDate));

  // Use the ShortDateFormat settings only
  ShowMessage('              ddddd = '+
              FormatDateTime('ddddd', myDate));

  // Use the LongDateFormat settings only
  ShowMessage('             dddddd = '+
              FormatDateTime('dddddd', myDate));

  // Use the ShortDateFormat + LongTimeFormat settings
  ShowMessage('                  c = '+
              FormatDateTime('c', myDate));
end;

Show full unit code

                 d/m/y = 9/2/00
              dd/mm/yy = 09/02/00
     ddd d of mmm yyyy = Wed 9 of Feb 2000
   dddd d of mmmm yyyy = Wednesday 9 of February 2000
                 ddddd = 09/02/2000
                dddddd = 09 February 2000
                     c = 09/02/2000 01:02:03

Example code : Showing all of the time field formatting data types

Show full unit code

        h:m:s.z = 1:2:3.4
   hh:mm:ss.zzz = 01:02:03.004
              t = 01:02
             tt = 01:02:03
              c = 09/02/2000 01:02:03

Example code : Showing the effect of local date format settings

var
  myDate : TDateTime;

begin
  // Set up our TDateTime variable with a full date and time
  myDate := StrToDateTime('09/02/49 01:02:03.004');

  // Demonstrate default locale settings

  // Use the DateSeparator and TimeSeparator values
  ShowMessage('dd/mm/yy hh:mm:ss = '+
              FormatDateTime('dd/mm/yy hh:mm:ss', myDate));

  // Use ShortMonthNames
  ShowMessage('              mmm = '+FormatDateTime('mmm', myDate));

  // Use LongMonthNames
  ShowMessage('             mmmm = '+FormatDateTime('mmmm', myDate));

  // Use ShortDayNames
  ShowMessage('              ddd = '+FormatDateTime('ddd', myDate));

  // Use LongDayNames
  ShowMessage('             dddd = '+FormatDateTime('dddd', myDate));

  // Use the ShortDateFormat string
  ShowMessage('            ddddd = '+FormatDateTime('ddddd', myDate));

  // Use the LongDateFormat string
  ShowMessage('           dddddd = '+FormatDateTime('dddddd', myDate));

  // Use the TimeAmString
  ShowMessage('           hhampm = '+FormatDateTime('hhampm', myDate));

  // Use the ShortTimeFormat string
  ShowMessage('                t = '+FormatDateTime('t', myDate));

  // Use the LongTimeFormat string
  ShowMessage('               tt = '+FormatDateTime('tt', myDate));

  // Use the TwoDigitCenturyWindow
  ShowMessage('       dd/mm/yyyy = '+
              FormatDateTime('dd/mm/yyyy', myDate));

  ShowMessage('');

  // Now change the defaults
  DateSeparator      := '-';
  TimeSeparator      := '_';
  ShortDateFormat    := 'dd/mmm/yy';
  LongDateFormat     := 'dddd dd of mmmm of yyyy';
  TimeAMString       := 'morning';
  TimePMString       := 'afternoon';
  ShortTimeFormat    := 'hh:mm:ss';
  LongTimeFormat     := 'hh : mm : ss . zzz';
  ShortMonthNames[2] := 'FEB';
  LongMonthNames[2]  := 'FEBRUARY';
  ShortDayNames[4]   := 'WED';
  LongDayNames[4]    := 'WEDNESDAY';
  TwoDigitYearCenturyWindow := 75;

  // Set up our TDateTime variable with the same value as before
  // except that we must use the new date and time separators
  // The TwoDigitYearCenturyWindow variable only takes effect here
  myDate := StrToDateTime('09-02-49 01_02_03.004');

  // Use the DateSeparator and TimeSeparator values
  ShowMessage('dd/mm/yy hh:mm:ss = '+
              FormatDateTime('dd/mm/yy hh:mm:ss', myDate));

  // Use ShortMonthNames
  ShowMessage('              mmm = '+FormatDateTime('mmm', myDate));

  // Use LongMonthNames
  ShowMessage('             mmmm = '+FormatDateTime('mmmm', myDate));

  // Use ShortDayNames
  ShowMessage('              ddd = '+FormatDateTime('ddd', myDate));

  // Use LongDayNames
  ShowMessage('             dddd = '+FormatDateTime('dddd', myDate));

  // Use the ShortDateFormat string
  ShowMessage('            ddddd = '+FormatDateTime('ddddd', myDate));

  // Use the LongDateFormat string
  ShowMessage('           dddddd = '+FormatDateTime('dddddd', myDate));

  // Use the TimeAmString
  ShowMessage('           hhampm = '+FormatDateTime('hhampm', myDate));

  // Use the ShortTimeFormat string
  ShowMessage('                t = '+FormatDateTime('t', myDate));

  // Use the LongTimeFormat string
  ShowMessage('               tt = '+FormatDateTime('tt', myDate));

  // Use the TwoDigitCenturyWindow
  ShowMessage('       dd/mm/yyyy = '+
              FormatDateTime('dd/mm/yyyy', myDate));
end;

Show full unit code

   dd/mm/yy hh:mm:ss = 09/02/49 01:02:03
                 mmm = Feb
                mmmm = February
                 ddd = Tue
                dddd = Tuesday
               ddddd = 09/02/2049
              dddddd = 09 February 2049
              hhampm = 01AM
                   t = 01:02
                  tt = 01:02:03
          dd/mm/yyyy = 09/02/2049

   dd/mm/yy hh:mm:ss = 09-02-49 01_02_03
                 mmm = FEB
                mmmm = FEBRUARY
                 ddd = WED
                dddd = WEDNESDAY
               ddddd = 09-FEB-49
              dddddd = WEDNESDAY 09 of FEBRUARY of 1949
              hhampm = 01morning
                   t = 01_02_03
                  tt = 01 _ 02 _ 03 . 004
          dd/mm/yyyy = 09-02-1949