Pascal - Date & Time

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Most of the softwares you write need implementing some form of date functions returning current date and time. Dates are so much part of everyday life that it becomes easy to work with them without thinking. Pascal also provides powerful tools for date arithmetic that makes manipulating dates easy. However, the actual name and workings of these functions are different for different compilers.

Getting the Current Date & Time:

Pascal's TimeToString function gives you the current time in a colon(: ) delimited form. The following example shows how to get the current time:

program TimeDemo;
uses sysutils;
begin
   writeln ('Current time : ',TimeToStr(Time));
end.

When the above code was compiled and executed, it produces the following result:

Current time : 18:33:08

The Date function returns the current date in TDateTime format. The TDateTime is a double value, which needs some decoding and formatting. The following program demonstrates how to use it in your program to display the current date:

Program DateDemo;
uses sysutils;
var
   YY,MM,DD : Word;
begin
   writeln ('Date : ',Date);
   DeCodeDate (Date,YY,MM,DD);
   writeln (format ('Today is (DD/MM/YY): %d/%d/%d ',[dd,mm,yy]));
 end.

When the above code was compiled and executed, it produces the following result:

Date: 4.111300000000000E+004
Today is (DD/MM/YY):23/7/2012

The Now function returns the current date and time:

Program DatenTimeDemo;
uses sysutils;
begin
   writeln ('Date and Time at the time of writing : ',DateTimeToStr(Now));
end.

When the above code was compiled and executed, it produces the following result:

Date and Time at the time of writing : 23/7/2012 18:51:

Free Pascal provides a simple time stamp structure named TTimeStamp, which has the following format:

type TTimeStamp = record
  Time: Integer;
  Date: Integer;
end;

Various Date & Time Functions:

Free Pascal provides the following date and time functions:

S.NFunction Name & Description
1function DateTimeToFileDate(DateTime: TDateTime):LongInt;
Converts DateTime type to file date.
2function DateTimeToStr( DateTime: TDateTime):;
Constructs string representation of DateTime
3function DateTimeToStr(DateTime: TDateTime; const FormatSettings: TFormatSettings):;
Constructs string representation of DateTime
4procedure DateTimeToString(out Result: ;const FormatStr: ;const DateTime: TDateTime);
Constructs string representation of DateTime
5procedure DateTimeToString( out Result: ; const FormatStr: ; const DateTime: TDateTime; const FormatSettings: TFormatSettings );
Constructs string representation of DateTime
6procedure DateTimeToSystemTime( DateTime: TDateTime; out SystemTime: TSystemTime );
Converts DateTime to system time
7function DateTimeToTimeStamp( DateTime: TDateTime):TTimeStamp;Converts DateTime to timestamp
8function DateToStr( Date: TDateTime ):;
Constructs string representation of date
9function DateToStr( Date: TDateTime; const FormatSettings: TFormatSettings ):;
Constructs string representation of date
10function Date: TDateTime;
Gets current date
11function DayOfWeek( DateTime: TDateTime ):Integer;
Gets day of week
12procedure DecodeDate( Date: TDateTime; out Year: Word; out Month: Word; out Day: Word );
Decodes DateTime to year month and day
13procedure DecodeTime( Time: TDateTime; out Hour: Word; out Minute: Word; out Second: Word; out MilliSecond: Word );
Decodes DateTime to hours, minutes and seconds
14function EncodeDate( Year: Word; Month: Word; Day: Word ):TDateTime;
Encodes year, day and month to DateTime
15function EncodeTime( Hour: Word; Minute: Word; Second: Word; MilliSecond: Word ):TDateTime;
Encodes hours, minutes and seconds to DateTime
16function FormatDateTime( const FormatStr: ; DateTime: TDateTime ):;
Returns string representation of DateTime
17function FormatDateTime( const FormatStr: ; DateTime: TDateTime; const FormatSettings: TFormatSettings ):;
Returns string representation of DateTime
18function IncMonth( const DateTime: TDateTime; NumberOfMonths: Integer = 1 ):TDateTime;
Adds 1 to month
19function IsLeapYear( Year: Word ):Boolean;
Determines if year is leap year
20function MSecsToTimeStamp( MSecs: Comp ):TTimeStamp;
Converts number of milliseconds to timestamp
21function Now: TDateTime;
Gets current date and time
22function StrToDateTime( const S: ):TDateTime;
Converts string to DateTime
23function StrToDateTime( const s: ShortString; const FormatSettings: TFormatSettings ):TDateTime;
Converts string to DateTime
24function StrToDateTime( const s: AnsiString; const FormatSettings: TFormatSettings ):TDateTime;
Converts string to DateTime
25function StrToDate( const S: ShortString ):TDateTime;
Converts string to date
26function StrToDate( const S: Ansistring ):TDateTime;
Converts string to date
27function StrToDate( const S: ShortString; separator: Char ):TDateTime;
Converts string to date
28function StrToDate( const S: AnsiString; separator: Char ):TDateTime;
Converts string to date
29function StrToDate( const S: ShortString; const useformat: ; separator: Char ):TDateTime;
Converts string to date
30function StrToDate( const S: AnsiString; const useformat: ; separator: Char ):TDateTime;
Converts string to date
31 function StrToDate( const S: PChar; Len: Integer; const useformat: ; separator: Char = #0 ):TDateTime;
Converts string to date
32function StrToTime( const S: Shortstring ):TDateTime;
Converts string to time
33function StrToTime( const S: Ansistring ):TDateTime;
Converts string to time
34function StrToTime( const S: ShortString; separator: Char ):TDateTime;
Converts string to time
35function StrToTime( const S: AnsiString; separator: Char ):TDateTime;
Converts string to time
36 function StrToTime( const S: ; FormatSettings: TFormatSettings ):TDateTime;
Converts string to time
37function StrToTime( const S: PChar; Len: Integer; separator: Char = #0 ):TDateTime;
Converts string to time
38function SystemTimeToDateTime( const SystemTime: TSystemTime ):TDateTime;
Converts system time to datetime
39function TimeStampToDateTime( const TimeStamp: TTimeStamp ):TDateTime;
Converts time stamp to DateTime
40function TimeStampToMSecs( const TimeStamp: TTimeStamp ):comp;
Converts Timestamp to number of milliseconds
41function TimeToStr( Time: TDateTime ):;
Returns string representation of Time
42function TimeToStr( Time: TDateTime; const FormatSettings: TFormatSettings ):;
Returns string representation of Time
43function Time: TDateTime;
Get current time

The following example illustrates the use of some of the above functions:

Program DatenTimeDemo;
uses sysutils;
var
year, month, day, hr, min, sec, ms: Word;
begin
   writeln ('Date and Time at the time of writing : ',DateTimeToStr(Now));
   writeln('Today is ',LongDayNames[DayOfWeek(Date)]);
   writeln;
   writeln('Details of Date: ');
   DecodeDate(Date,year,month,day);
   writeln (Format ('Day: %d',[day]));
   writeln (Format ('Month: %d',[month]));
   writeln (Format ('Year: %d',[year]));
   writeln;
   writeln('Details of Time: ');
   DecodeTime(Time,hr, min, sec, ms);
   writeln (format('Hour: %d:',[hr]));
   writeln (format('Minutes: %d:',[min]));
   writeln (format('Seconds: %d:',[sec]));
   writeln (format('Milliseconds: %d:',[hr]));
end.

When the above code was compiled and executed, it produced the following result:

Date and Time at the time of writing : 7/24/2012 8:26:
Today is Tuesday
Details of Date:
Day:24
Month:7
Year: 2012
Details of Time:
Hour: 8
Minutes: 26
Seconds: 21
Milliseconds: 8


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