Pascal - Date and Time

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.
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;
Free Pascal provides the following date and time functions −
function DateTimeToFileDate(DateTime: TDateTime):LongInt;
Converts DateTime type to file date.
function DateTimeToStr( DateTime: TDateTime):; 
Constructs string representation of DateTime
function DateTimeToStr(DateTime: TDateTime; const FormatSettings: TFormatSettings):;
Constructs string representation of DateTime
procedure DateTimeToString(out Result: ;const FormatStr: ;const DateTime: TDateTime);
Constructs string representation of DateTime
procedure DateTimeToString(out Result: ; const FormatStr: ; const DateTime: TDateTime; const FormatSettings: TFormatSettings);
Constructs string representation of DateTime
procedure DateTimeToSystemTime(DateTime: TDateTime; out SystemTime: TSystemTime);
Converts DateTime to system time
function DateTimeToTimeStamp( DateTime: TDateTime):TTimeStamp;Converts DateTime to timestamp
function DateToStr(Date: TDateTime):;
Constructs string representation of date
function DateToStr(Date: TDateTime; const FormatSettings: TFormatSettings):;
Constructs string representation of date
function Date: TDateTime;
Gets current date
function DayOfWeek(DateTime: TDateTime):Integer;
Gets day of week
procedure DecodeDate(Date: TDateTime; out Year: Word; out Month: Word; out Day: Word);
Decodes DateTime to year month and day
procedure DecodeTime(Time: TDateTime; out Hour: Word; out Minute: Word; out Second: Word;  out MilliSecond: Word);
Decodes DateTime to hours, minutes and seconds
function EncodeDate(Year: Word; Month: Word; Day: Word):TDateTime; 
Encodes year, day and month to DateTime
function EncodeTime(Hour: Word; Minute: Word; Second: Word; MilliSecond: Word):TDateTime; 
Encodes hours, minutes and seconds to DateTime
function FormatDateTime(const FormatStr: ; DateTime: TDateTime):;
Returns string representation of DateTime
function FormatDateTime(const FormatStr: ; DateTime: TDateTime; const FormatSettings: TFormatSettings):;
Returns string representation of DateTime
function IncMonth(const DateTime: TDateTime; NumberOfMonths: Integer = 1):TDateTime;
Adds 1 to month
function IsLeapYear(Year: Word):Boolean;
Determines if year is leap year
function MSecsToTimeStamp(MSecs: Comp):TTimeStamp;
Converts number of milliseconds to timestamp
function Now: TDateTime;
Gets current date and time
function StrToDateTime(const S:):TDateTime;
Converts string to DateTime
function StrToDateTime(const s: ShortString; const FormatSettings: TFormatSettings):TDateTime;
Converts string to DateTime
function StrToDateTime(const s: AnsiString; const FormatSettings: TFormatSettings):TDateTime;
Converts string to DateTime
function StrToDate(const S: ShortString):TDateTime;
Converts string to date
function StrToDate(const S: Ansistring):TDateTime;
Converts string to date
function StrToDate(const S: ShortString; separator: Char):TDateTime;
Converts string to date
function StrToDate(const S: AnsiString; separator: Char):TDateTime;
Converts string to date
function StrToDate(const S: ShortString; const useformat: ; separator: Char):TDateTime;

Converts string to date
function StrToDate(const S: AnsiString; const useformat: ; separator: Char):TDateTime;
Converts string to date
function StrToDate(const S: PChar; Len: Integer; const useformat: ; separator: Char = #0):TDateTime;
Converts string to date
function StrToTime(const S: Shortstring):TDateTime;
Converts string to time
function StrToTime(const S: Ansistring):TDateTime;
Converts string to time
function StrToTime(const S: ShortString; separator: Char):TDateTime;
Converts string to time
function StrToTime(const S: AnsiString; separator: Char):TDateTime;
Converts string to time
function StrToTime(const S: ; FormatSettings: TFormatSettings):TDateTime;
Converts string to time
function StrToTime(const S: PChar; Len: Integer; separator: Char = #0):TDateTime;
Converts string to time
function SystemTimeToDateTime(const SystemTime: TSystemTime):TDateTime;
Converts system time to datetime
function TimeStampToDateTime(const TimeStamp: TTimeStamp):TDateTime;
Converts time stamp to DateTime
function TimeStampToMSecs(const TimeStamp: TTimeStamp):comp;
Converts Timestamp to number of milliseconds
function TimeToStr(Time: TDateTime):;
Returns string representation of Time
function TimeToStr(Time: TDateTime; const FormatSettings: TFormatSettings):;
Returns string representation of Time
function 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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