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Days between dates

From Rosetta Code
Days between dates is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.
Task

Calculate the number of days between two dates.

Date input should be of the form   YYYY-MM-DD.


Motivation

To demonstrate one of the numerous ways this can be done.

Ada[edit]

with Ada.Calendar;
with Ada.Text_IO;
with Ada.Integer_Text_IO;
 
with GNAT.Calendar.Time_IO;
 
procedure Days_Between_Dates is
 
function Days_Between (Lower_Date  : in Ada.Calendar.Time;
Higher_Date : in Ada.Calendar.Time) return Integer
is
use Ada.Calendar;
Diff : constant Duration := Higher_Date - Lower_Date;
begin
return Integer (Diff / Day_Duration'Last);
end Days_Between;
 
procedure Put_Days_Between (Lower_Date  : in String;
Higher_Date : in String;
Comment  : in String)
is
use Ada.Text_IO;
use Ada.Integer_Text_IO;
use GNAT.Calendar.Time_IO;
 
Diff : constant Integer := Days_Between (Lower_Date => Value (Lower_Date),
Higher_Date => Value (Higher_Date));
begin
Put ("Days between " & Lower_Date & " and " & Higher_Date & " is ");
Put (Diff, Width => 5);
Put (" days -- ");
Put (Comment);
New_Line;
end Put_Days_Between;
 
begin
Put_Days_Between ("1995-11-21", "1995-11-21", "Identical dates");
Put_Days_Between ("2019-01-01", "2019-01-02", "Positive span");
Put_Days_Between ("2019-01-02", "2019-01-01", "Negative span");
Put_Days_Between ("2019-01-01", "2019-03-01", "Non-leap year");
Put_Days_Between ("2020-01-01", "2020-03-01", "Leap year");
Put_Days_Between ("1902-01-01", "1968-12-25", "Past");
Put_Days_Between ("2090-01-01", "2098-12-25", "Future");
Put_Days_Between ("1902-01-01", "2098-12-25", "Long span");
end Days_Between_Dates;
Output:
Days between 1995-11-21 and 1995-11-21 is     0 days  --  Identical dates
Days between 2019-01-01 and 2019-01-02 is     1 days  --  Positive span
Days between 2019-01-02 and 2019-01-01 is    -1 days  --  Negative span
Days between 2019-01-01 and 2019-03-01 is    59 days  --  Non-leap year
Days between 2020-01-01 and 2020-03-01 is    60 days  --  Leap year
Days between 1902-01-01 and 1968-12-25 is 24465 days  --  Past
Days between 2090-01-01 and 2098-12-25 is  3280 days  --  Future
Days between 1902-01-01 and 2098-12-25 is 71947 days  --  Long span

AppleScript[edit]

on daysBetweenDates(date1, date2)
considering numeric strings -- Allows for leading zeros having been omitted.
if (date1 = date2) then return date1 & " and " & date2 & " are the same date"
end considering
 
-- Get the components of each date.
set astid to AppleScript's text item delimiters
set AppleScript's text item delimiters to "-"
set {y1, m1, d1} to date1's text items
set {y2, m2, d2} to date2's text items
set AppleScript's text item delimiters to astid
 
-- Derive AppleScript date objects.
-- The best way to do this generally is to use the 'current date' function to obtain a date object
-- and then to set the properties of the result (or of a copy) to the required values.
-- The initial setting of the day values to 1 is to prevent overflow due to possibly
-- incompatible day and month values during the sequential setting of the properties.
-- The integer values set here are automatically coerced from the text values obtained above.
tell (current date) to set {its day, its year, its month, its day, its time, firstDate} to {1, y1, m1, d1, 0, it}
copy firstDate to secondDate
tell secondDate to set {its day, its year, its month, its day} to {1, y2, m2, d2}
 
-- Do the math.
set daysDifference to (firstDate - secondDate) div days
 
-- Format some output.
if (daysDifference > 0) then
return date1 & " comes " & daysDifference & " day" & item (((daysDifference is 1) as integer) + 1) of {"s", ""} & ¬
" after " & date2
else
return date1 & " comes " & -daysDifference & " day" & item (((daysDifference is -1) as integer) + 1) of {"s", ""} & ¬
" before " & date2
end if
end daysBetweenDates
 
return daysBetweenDates("2020-04-11", "2001-01-01") & linefeed & ¬
daysBetweenDates("2020-04-11", "2020-04-12") & linefeed & ¬
daysBetweenDates("2020-04-11", "2020-04-11")
Output:
"2020-04-11 comes 7040 days after 2001-01-01
2020-04-11 comes 1 day before 2020-04-12
2020-04-11 and 2020-04-11 are the same date"


Or, composing a function from reusable generics, and drawing on NSISO8601DateFormatter:

use AppleScript version "2.4"
use framework "Foundation"
use scripting additions
 
 
-- daysBetween :: String -> String -> Int
on daysBetween(iso8601From, iso8601To)
set midnight to "T00:00:00+00:00"
((dateFromISO8601(iso8601To & midnight) - ¬
dateFromISO8601(iso8601From & midnight)) / 86400) as integer
end daysBetween
 
 
-- dateFromISO8601 :: String -> Date
on dateFromISO8601(isoDateString)
set ca to current application
tell ca's NSISO8601DateFormatter's alloc's init()
set its formatOptions to ¬
(ca's NSISO8601DateFormatWithInternetDateTime as integer)
(its dateFromString:(isoDateString)) as date
end tell
end dateFromISO8601
 
 
---------------------------TEST----------------------------
on run
script test
on |λ|(ab)
set {a, b} to ab
set delta to daysBetween(a, b)
(a & " -> " & b & " -> " & ¬
justifyRight(5, space, delta as string)) & ¬
pluralize(delta, " day")
end |λ|
end script
 
unlines(map(test, {¬
{"2020-04-11", "2001-01-01"}, ¬
{"2020-04-11", "2020-04-12"}, ¬
{"2020-04-11", "2020-04-11"}, ¬
{"2019-01-01", "2019-09-30"}}))
end run
 
 
 
--------------------GENERIC FUNCTIONS ---------------------
 
-- Absolute value.
-- abs :: Num -> Num
on abs(x)
if 0 > x then
-x
else
x
end if
end abs
 
 
-- justifyRight :: Int -> Char -> String -> String
on justifyRight(n, cFiller, strText)
if n > length of strText then
text -n thru -1 of ((replicate(n, cFiller) as text) & strText)
else
strText
end if
end justifyRight
 
 
-- map :: (a -> b) -> [a] -> [b]
on map(f, xs)
-- The list obtained by applying f
-- to each element of xs.
tell mReturn(f)
set lng to length of xs
set lst to {}
repeat with i from 1 to lng
set end of lst to |λ|(item i of xs, i, xs)
end repeat
return lst
end tell
end map
 
 
-- mReturn :: First-class m => (a -> b) -> m (a -> b)
on mReturn(f)
-- 2nd class handler function lifted into 1st class script wrapper.
if script is class of f then
f
else
script
property |λ| : f
end script
end if
end mReturn
 
 
-- pluralize :: Int -> String -> String
on pluralize(n, s)
set m to abs(n)
if 0 = m or 2 ≤ m then
s & "s"
else
s
end if
end pluralize
 
 
-- replicate :: Int -> String -> String
on replicate(n, s)
set out to ""
if n < 1 then return out
set dbl to s
 
repeat while (n > 1)
if (n mod 2) > 0 then set out to out & dbl
set n to (n div 2)
set dbl to (dbl & dbl)
end repeat
return out & dbl
end replicate
 
 
-- unlines :: [String] -> String
on unlines(xs)
-- A single string formed by the intercalation
-- of a list of strings with the newline character.
set {dlm, my text item delimiters} to ¬
{my text item delimiters, linefeed}
set str to xs as text
set my text item delimiters to dlm
str
end unlines
Output:
2020-04-11 -> 2001-01-01 -> -7040 days
2020-04-11 -> 2020-04-12 ->     1 day
2020-04-11 -> 2020-04-11 ->     0 days
2019-01-01 -> 2019-09-30 ->   272 days

AWK[edit]

 
# syntax: GAWK -f DAYS_BETWEEN_DATES.AWK
BEGIN {
regexp = "^....-..-..$" # YYYY-MM-DD
main("1969-12-31","1970-01-01","builtin has bad POSIX start date")
main("1970-01-01","2038-01-19","builtin has bad POSIX stop date")
main("1970-01-01","2019-10-02","format OK")
main("1970-01-01","2019/10/02","format NG")
main("1995-11-21","1995-11-21","identical dates")
main("2019-01-01","2019-01-02","positive date")
main("2019-01-02","2019-01-01","negative date")
main("2019-01-01","2019-03-01","non-leap year")
main("2020-01-01","2020-03-01","leap year")
exit(0)
}
function main(date1,date2,comment, d1,d2,diff) {
printf("\t%s\n",comment)
d1 = days_builtin(date1)
d2 = days_builtin(date2)
diff = (d1 == "" || d2 == "") ? "error" : d2-d1
printf("builtin %10s to %10s = %s\n",date1,date2,diff)
d1 = days_generic(date1)
d2 = days_generic(date2)
diff = (d1 == "" || d2 == "") ? "error" : d2-d1
printf("generic %10s to %10s = %s\n",date1,date2,diff)
}
function days_builtin(ymd) { # use gawk builtin
if (ymd !~ regexp) { return("") }
if (ymd < "1970-01-01" || ymd > "2038-01-18") { return("") } # outside POSIX range
gsub(/-/," ",ymd)
return(int(mktime(sprintf("%s 0 0 0",ymd)) / (60*60*24)))
}
function days_generic(ymd, d,m,y,result) { # use Python formula
if (ymd !~ regexp) { return("") }
y = substr(ymd,1,4)
m = substr(ymd,6,2)
d = substr(ymd,9,2)
m = (m + 9) % 12
y = int(y - int(m/10))
result = 365*y + int(y/4) - int(y/100) + int(y/400) + int((m*306+5)/10) + (d-1)
return(result)
}
 
Output:
    builtin has bad POSIX start date
builtin 1969-12-31 to 1970-01-01 = error
generic 1969-12-31 to 1970-01-01 = 1
    builtin has bad POSIX stop date
builtin 1970-01-01 to 2038-01-19 = error
generic 1970-01-01 to 2038-01-19 = 24855
    format OK
builtin 1970-01-01 to 2019-10-02 = 18171
generic 1970-01-01 to 2019-10-02 = 18171
    format NG
builtin 1970-01-01 to 2019/10/02 = error
generic 1970-01-01 to 2019/10/02 = error
    identical dates
builtin 1995-11-21 to 1995-11-21 = 0
generic 1995-11-21 to 1995-11-21 = 0
    positive date
builtin 2019-01-01 to 2019-01-02 = 1
generic 2019-01-01 to 2019-01-02 = 1
    negative date
builtin 2019-01-02 to 2019-01-01 = -1
generic 2019-01-02 to 2019-01-01 = -1
    non-leap year
builtin 2019-01-01 to 2019-03-01 = 59
generic 2019-01-01 to 2019-03-01 = 59
    leap year
builtin 2020-01-01 to 2020-03-01 = 60
generic 2020-01-01 to 2020-03-01 = 60

C[edit]

 
#include<stdbool.h>
#include<string.h>
#include<stdio.h>
 
typedef struct{
int year, month, day;
}date;
 
date extractDate(char* str){
return (date){.year = 1000 * (str[0]-'0') + 100 * (str[1]-'0') + 10 * (str[2]-'0') + (str[3]-'0'), .month = 10*(str[5]-'0') + (str[6]-'0'), .day = 10*(str[8]-'0') + (str[9]-'0')};
}
 
bool isValidDate(char* str){
date newDate;
 
if(strlen(str)!=10 && str[4]!='-' && str[7]!='-'){
return false;
}
 
newDate = extractDate(str);
 
if(newDate.year<=0 || newDate.month<=0 || newDate.day<=0 || newDate.month>12 || (newDate.month==2 && newDate.day>29) ||
((newDate.month==1 || newDate.month==3 || newDate.month==5 || newDate.month==7 || newDate.month==8 || newDate.month==10 || newDate.month==12) && newDate.day>31) ||
newDate.day>30 || (newDate.year%4==0 && newDate.month==2 && newDate.month>28)){
return false;
}
 
return true;
}
 
int diffDays(date date1,date date2){
int days1, days2;
 
date1.month = (date1.month + 9)%12;
date1.year = date1.year - date1.month/10;
 
date2.month = (date2.month + 9)%12;
date2.year = date2.year - date2.month/10;
 
days1 = 365*date1.year + date1.year/4 - date1.year/100 + date1.year/400 + (date1.month*306 + 5)/10 + ( date1.day - 1 );
days2 = 365*date2.year + date2.year/4 - date2.year/100 + date2.year/400 + (date2.month*306 + 5)/10 + ( date2.day - 1 );
 
return days2 - days1;
}
 
int main(int argc,char** argv)
{
if(argc!=3){
return printf("Usage : %s <yyyy-mm-dd> <yyyy-mm-dd>",argv[0]);
}
 
if(isValidDate(argv[1])&&isValidDate(argv[2]) == false){
return printf("Dates are invalid.\n");
}
 
printf("Days Difference : %d\n", diffDays(extractDate(argv[1]),extractDate(argv[2])));
 
return 0;
}
 

Output :

[email protected]:~/doodles$ ./a.out 2019-01-01 2019-12-02
Days Difference : 335

C++[edit]

Translation of: c
#include <iomanip>
#include <iostream>
 
class Date {
private:
int year, month, day;
 
public:
Date(std::string str) {
if (isValidDate(str)) {
year = atoi(&str[0]);
month = atoi(&str[5]);
day = atoi(&str[8]);
} else {
throw std::exception("Invalid date");
}
}
 
int getYear() {
return year;
}
 
int getMonth() {
return month;
}
 
int getDay() {
return day;
}
 
// YYYY-MM-DD
static bool isValidDate(std::string str) {
if (str.length() != 10 || str[4] != '-' || str[7] != '-') {
return false;
}
 
if (!isdigit(str[0]) || !isdigit(str[1]) || !isdigit(str[2]) || !isdigit(str[3])) {
return false; // the year is not valid
}
if (!isdigit(str[5]) || !isdigit(str[6])) {
return false; // the month is not valid
}
if (!isdigit(str[8]) || !isdigit(str[9])) {
return false; // the day is not valid
}
 
int year = atoi(&str[0]);
int month = atoi(&str[5]);
int day = atoi(&str[8]);
 
// quick checks
if (year <= 0 || month <= 0 || day <= 0) {
return false;
}
if (month > 12) {
return false;
}
 
switch (month) {
case 2:
if (day > 29) {
return false;
}
if (!isLeapYear(year) && day == 29) {
return false;
}
break;
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
if (day > 31) {
return false;
}
break;
default:
if (day > 30) {
return false;
}
break;
}
 
return true;
}
 
static bool isLeapYear(int year) {
if (year > 1582) {
return ((year % 4 == 0) && (year % 100 > 0))
|| (year % 400 == 0);
}
if (year > 10) {
return year % 4 == 0;
}
// not bothering with earlier leap years
return false;
}
 
friend std::ostream &operator<<(std::ostream &, Date &);
};
 
std::ostream &operator<<(std::ostream &os, Date &d) {
os << std::setfill('0') << std::setw(4) << d.year << '-';
os << std::setfill('0') << std::setw(2) << d.month << '-';
os << std::setfill('0') << std::setw(2) << d.day;
return os;
}
 
int diffDays(Date date1, Date date2) {
int d1m = (date1.getMonth() + 9) % 12;
int d1y = date1.getYear() - d1m / 10;
 
int d2m = (date2.getMonth() + 9) % 12;
int d2y = date2.getYear() - d2m / 10;
 
int days1 = 365 * d1y + d1y / 4 - d1y / 100 + d1y / 400 + (d1m * 306 + 5) / 10 + (date1.getDay() - 1);
int days2 = 365 * d2y + d2y / 4 - d2y / 100 + d2y / 400 + (d2m * 306 + 5) / 10 + (date2.getDay() - 1);
 
return days2 - days1;
}
 
int main() {
std::string ds1 = "2019-01-01";
std::string ds2 = "2019-12-02";
 
if (Date::isValidDate(ds1) && Date::isValidDate(ds2)) {
Date d1(ds1);
Date d2(ds2);
std::cout << "Days difference : " << diffDays(d1, d2);
} else {
std::cout << "Dates are invalid.\n";
}
 
return 0;
}
Output:
Days difference : 335

Alternative using Boost[edit]

Library: Boost
#include <cstdlib>
#include <iostream>
#include <boost/date_time/gregorian/gregorian.hpp>
 
int main(int argc, char** argv) {
using namespace boost::gregorian;
if (argc != 3) {
std::cerr << "usage: " << argv[0] << " start-date end-date\n";
return EXIT_FAILURE;
}
try {
date start_date(from_simple_string(argv[1]));
date end_date(from_simple_string(argv[2]));
std::cout << end_date - start_date << '\n';
} catch (const std::exception& ex) {
std::cerr << ex.what() << '\n';
return EXIT_FAILURE;
}
return EXIT_SUCCESS;
}
Output:
./days_between_dates 2020-01-01 2020-09-06
249

C#[edit]

using System;
using System.Globalization;
 
public class Program
{
public static void Main() => WriteLine(DateDiff("1970-01-01", "2019-10-18"));
 
public static int DateDiff(string d1, string d2) {
var a = DateTime.ParseExact(d1, "yyyy-MM-dd", CultureInfo.InvariantCulture);
var b = DateTime.ParseExact(d2, "yyyy-MM-dd", CultureInfo.InvariantCulture);
return (int)(b - a).TotalDays;
}
}
Output:
18187

COBOL[edit]

Works with: GnuCOBOL
COBOL *> days-between
*> Tectonics: cobc -xj days-between.cob
 
identification division.
program-id. days-between.
 
procedure division.
compute tally =
function integer-of-formatted-date('YYYY-MM-DD', '2019-11-24')
-
function integer-of-formatted-date('YYYY-MM-DD', '2000-01-01')
display tally
 
compute tally =
function integer-of-formatted-date('YYYYMMDD', '20191124')
-
function integer-of-formatted-date('YYYYMMDD', '20000101')
display tally
 
goback.
end program days-between.
Output:
prompt$ cobc -xj days-between-dates.cob
07267
07267

D[edit]

import std.datetime.date;
import std.stdio;
 
void main() {
auto fromDate = Date.fromISOExtString("2019-01-01");
auto toDate = Date.fromISOExtString("2019-10-07");
auto diff = toDate - fromDate;
writeln("Number of days between ", fromDate, " and ", toDate, ": ", diff.total!"days");
}
Output:
Number of days between 2019-Jan-01 and 2019-Oct-07: 279

Delphi[edit]

Translation of: C#
 
program Days_between_dates;
 
{$APPTYPE CONSOLE}
 
uses
System.SysUtils;
 
function CreateFormat(fmt: string; Delimiter: Char): TFormatSettings;
begin
Result := TFormatSettings.Create();
with Result do
begin
DateSeparator := Delimiter;
ShortDateFormat := fmt;
end;
end;
 
function DaysBetween(Date1, Date2: string): Integer;
var
dt1, dt2: TDateTime;
fmt: TFormatSettings;
begin
fmt := CreateFormat('yyyy-mm-dd', '-');
dt1 := StrToDate(Date1, fmt);
dt2 := StrToDate(Date2, fmt);
Result := Trunc(dt2 - dt1);
end;
 
begin
Writeln(DaysBetween('1970-01-01', '2019-10-18'));
readln;
end.
Output:
18187

Erlang[edit]

 
 
-module(daysbetween).
-export([between/2,dateToInts/2]).
 
% Return Year or Month or Date from datestring
dateToInts(String, POS) ->
list_to_integer( lists:nth( POS, string:tokens(String, "-") ) ).
 
% Alternative form of above
% dateToInts(String,POS) ->
% list_to_integer( lists:nth( POS, re:split(String ,"-", [{return,list},trim]) ) ).
 
% Return the number of days between dates formatted "2019-09-30"
between(DateOne,DateTwo) ->
L = [1,2,3],
[Y1,M1,D1] = [ dateToInts(DateOne,X) || X <- L],
[Y2,M2,D2] = [ dateToInts(DateTwo,X) || X <- L],
GregOne = calendar:date_to_gregorian_days(Y1,M1,D1),
GregTwo = calendar:date_to_gregorian_days(Y2,M2,D2),
GregTwo - GregOne.
 
 
 
Output:

erlang shell:

30> c(daysbetween).
c(daysbetween).
{ok,daysbetween}
31> daysbetween:between("2019-01-01", "2019-09-30").
daysbetween:between("2019-01-01", "2019-09-30").
272

Factor[edit]

Factor supports the addition and subtraction of timestamps and durations with the time+ and time- words.

USING: calendar calendar.parser kernel math prettyprint ;
 
: days-between ( ymd-str ymd-str -- n )
[ ymd>timestamp ] [email protected] time- duration>days abs ;
 
"2019-01-01" "2019-09-30" days-between .
"2016-01-01" "2016-09-30" days-between .  ! leap year
Output:
272
273

Go[edit]

package main
 
import (
"fmt"
"log"
"time"
)
 
const layout = "2006-01-02" // template for time.Parse
 
// Parameters assumed to be in YYYY-MM-DD format.
func daysBetween(date1, date2 string) int {
t1, err := time.Parse(layout, date1)
check(err)
t2, err := time.Parse(layout, date2)
check(err)
days := int(t1.Sub(t2).Hours() / 24)
if days < 0 {
days = -days
}
return days
}
 
func check(err error) {
if err != nil {
log.Fatal(err)
}
}
 
func main() {
date1, date2 := "2019-01-01", "2019-09-30"
days := daysBetween(date1, date2)
fmt.Printf("There are %d days between %s and %s\n", days, date1, date2)
 
date1, date2 = "2015-12-31", "2016-09-30"
days = daysBetween(date1, date2)
fmt.Printf("There are %d days between %s and %s\n", days, date1, date2)
}
Output:
There are 272 days between 2019-01-01 and 2019-09-30
There are 274 days between 2015-12-31 and 2016-09-30

Groovy[edit]

Translation of: Kotlin
Translation of: Java
import java.time.LocalDate
 
def fromDate = LocalDate.parse("2019-01-01")
def toDate = LocalDate.parse("2019-10-19")
def diff = fromDate - toDate
println "Number of days between ${fromDate} and ${toDate}: ${diff}"
Output:
Number of days between 2019-01-01 and 2019-10-19: 291

Haskell[edit]

import Data.Time (Day)
import Data.Time.Calendar (diffDays)
import Data.Time.Format (parseTimeM,defaultTimeLocale)
 
main = do
putStrLn $ task "2019-01-01" "2019-09-30"
putStrLn $ task "2015-12-31" "2016-09-30"
 
task :: String -> String -> String
task xs ys = "There are " ++ (show $ betweenDays xs ys) ++ " days between " ++ xs ++ " and " ++ ys ++ "."
 
betweenDays :: String -> String -> Integer
betweenDays date1 date2 = go (stringToDay date1) (stringToDay date2)
where
go (Just x) (Just y) = diffDays y x
go Nothing _ = error "Exception: Bad format first date"
go _ Nothing = error "Exception: Bad format second date"
 
stringToDay :: String -> Maybe Day
stringToDay date = parseTimeM True defaultTimeLocale "%Y-%-m-%-d" date
Output:
There are 272 days between 2019-01-01 and 2019-09-30.
There are 274 days between 2015-12-31 and 2016-09-30.

Java[edit]

Translation of: Kotlin
import java.time.LocalDate;
import java.time.temporal.ChronoUnit;
 
public class DaysBetweenDates {
public static void main(String[] args) {
LocalDate fromDate = LocalDate.parse("2019-01-01");
LocalDate toDate = LocalDate.parse("2019-10-19");
long diff = ChronoUnit.DAYS.between(fromDate, toDate);
System.out.printf("Number of days between %s and %s: %d\n", fromDate, toDate, diff);
}
}
Output:
Number of days between 2019-01-01 and 2019-10-19: 291

Julia[edit]

using Dates
 
@show Day(DateTime("2019-09-30") - DateTime("2019-01-01"))
 
@show Day(DateTime("2019-03-01") - DateTime("2019-02-01"))
 
@show Day(DateTime("2020-03-01") - DateTime("2020-02-01"))
 
@show Day(DateTime("2029-03-29") - DateTime("2019-03-29"))
 
Output:
Day(DateTime("2019-09-30") - DateTime("2019-01-01")) = 272 days
Day(DateTime("2019-03-01") - DateTime("2019-02-01")) = 28 days
Day(DateTime("2020-03-01") - DateTime("2020-02-01")) = 29 days
Day(DateTime("2029-03-29") - DateTime("2019-03-29")) = 3653 days

Kotlin[edit]

import java.time.LocalDate
import java.time.temporal.ChronoUnit
 
fun main() {
val fromDate = LocalDate.parse("2019-01-01")
val toDate = LocalDate.parse("2019-10-19")
val diff = ChronoUnit.DAYS.between(fromDate, toDate)
println("Number of days between $fromDate and $toDate: $diff")
}
Output:
Number of days between 2019-01-01 and 2019-10-19: 291

Lua[edit]

This uses os.difftime to compare two Epoch times. Not to be used with dates before 1970.

SECONDS_IN_A_DAY = 60 * 60 * 24
 
-- Convert date string as YYYY-MM-DD to Epoch time.
function parseDate (str)
local y, m, d = string.match(str, "(%d+)-(%d+)-(%d+)")
return os.time({year = y, month = m, day = d})
end
 
-- Main procedure
io.write("Enter date 1: ")
local d1 = parseDate(io.read())
io.write("Enter date 2: ")
local d2 = parseDate(io.read())
local diff = math.ceil(os.difftime(d2, d1) / SECONDS_IN_A_DAY)
print("There are " .. diff .. " days between these dates.")
Output:
Enter date 1: 1970-01-01
Enter date 2: 2019-10-02
There are 18171 days between these dates.

Perl[edit]

Would not reinvent this wheel.

use feature 'say';
use Date::Calc qw(Delta_Days);
 
say Delta_Days(2018,7,13, 2019,9,13); # triskaidekaphobia
say Delta_Days(1900,1,1, 2000,1,1); # a century
say Delta_Days(2000,1,1, 2100,1,1); # another, with one extra leap day
say Delta_Days(2020,1,1, 2019,10,1); # backwards in time
say Delta_Days(2019,2,29, 2019,3,1); # croaks
Output:
427
36524
36525
-92
Date::Calc::PP::Delta_Days(): Date::Calc::Delta_Days(): not a valid date at Days_between_dates line 10

Phix[edit]

include builtins\timedate.e 
-- specify as many or as few permitted formats as you like:
set_timedate_formats({"YYYY-MM-DD","DD/MM/YYYY","YYYY/MM/DD"})
 
constant SECONDS_TO_DAYS = 60*60*24
 
procedure test(string d1, d2, desc="")
timedate td1 = parse_date_string(d1),
td2 = parse_date_string(d2)
atom s = timedate_diff(td1,td2,DT_DAY),
d = s/SECONDS_TO_DAYS
string e = elapsed(s)&desc
printf(1,"Days between %s and %s: %d [%s]\n",{d1,d2,d,e})
end procedure
test("1969-12-31","1970-01-01")
test("1995-11-21","1995-11-21",", same date")
test("2019-01-02","2019-01-01",", negative date")
test("2019-01-01","2019-03-01",", non-leap year")
test("2020-01-01","2020-03-01",", leap year")
test("1970-01-01", "2019/10/18")
test("1970-01-01", "18/10/2019")

As shown, timedate_diff() can optionally round to the nearest whole number of days [else omit DT_DAY].
Note that elapsed() assumes all years are exactly 365 days, and in no way takes leap years into consideration (as opposed, of course, to timedate_diff() which handles them flawlessly), not that you sh/c/would ever use the string output of elapsed() in any further calculations anyway.

Output:
Days between 1969-12-31 and 1970-01-01: 1 [1 day]
Days between 1995-11-21 and 1995-11-21: 0 [0s, same date]
Days between 2019-01-02 and 2019-01-01: -1 [minus 1 day, negative date]
Days between 2019-01-01 and 2019-03-01: 59 [59 days, non-leap year]
Days between 2020-01-01 and 2020-03-01: 60 [60 days, leap year]
Days between 1970-01-01 and 2019/10/18: 18187 [49 years, 302 days]
Days between 1970-01-01 and 18/10/2019: 18187 [49 years, 302 days]

Python[edit]

 
 
#!/usr/bin/python
import sys
 
''' Difference between two dates = g(y2,m2,d2) - g(y1,m1,d1)
Where g() gives us the Gregorian Calendar Day
Inspired by discussion at:
https://stackoverflow.com/questions/12862226/the-implementation-of-calculating-the-number-of-days-between-2-dates
'''

 
def days( y,m,d ):
''' input year and month are shifted to begin the year in march'''
m = (m + 9) % 12
y = y - m/10
 
''' with (m*306 + 5)/10 the number of days from march 1 to the current 'm' month '''
result = 365*y + y/4 - y/100 + y/400 + (m*306 + 5)/10 + ( d - 1 )
return result
 
def diff(one,two):
[y1,m1,d1] = one.split('-')
[y2,m2,d2] = two.split('-')
# strings to integers
year2 = days( int(y2),int(m2),int(d2))
year1 = days( int(y1), int(m1), int(d1) )
return year2 - year1
 
if __name__ == "__main__":
one = sys.argv[1]
two = sys.argv[2]
print diff(one,two)
 
Output:
python days-between.py 2019-01-01 2019-09-30
272

Raku[edit]

(formerly Perl 6) Dates are first class objects in Raku and may have arithmetic in days done directly on them.

say Date.new('2019-09-30') - Date.new('2019-01-01');
 
say Date.new('2019-03-01') - Date.new('2019-02-01');
 
say Date.new('2020-03-01') - Date.new('2020-02-01');
 
say Date.new('2029-03-29') - Date.new('2019-03-29');
 
say Date.new('2019-01-01') + 90;
 
say Date.new('2020-01-01') + 90;
 
say Date.new('2019-02-29') + 30;
 
CATCH { default { .message.say; exit; } };
272
28
29
3653
2019-04-01
2020-03-31
Day out of range. Is: 29, should be in 1..28

REBOL[edit]

REBOL accepts a multitude of lexically recognized date! formats. date! is a builtin datatype. Slashes or dashes, year-month-day, day/month/year, or dd/monthname/year, etc. Math on dates defaults to days.

prompt$ rebol -q
>> 2019-11-24 - 2000-01-01
== 7267
>> 2019-nov-24 - 01-jan-2000
== 7267

REXX[edit]

Works with: Regina REXX

bare bones version[edit]

Programming note:   the   B   (Base)   an option for the   date   BIF which indicates to compute the number of
days since the beginning of the Gregorian calendar,   and   I   which is the option that indicates the date is in
the   ISO   (International Standards Organization standard 8601:2004)   format.

/*REXX program computes the number of days between two dates in the form of  YYYY-MM-DD */
parse arg $1 $2 . /*get 2 arguments (dates) from the C.L.*/
say abs( date('B',$1,"I") - date('B',$2,"I") ) ' days between ' $1 " and " $2
/*stick a fork in it, we're all done. */
output   when using the inputs of:     2019-10-02   2000-01-01
7214  days between  2019-10-02  and  2000-01-01

supports more variations[edit]

This REXX version supports more variations in the date format   (allows a single digit month and/or day), as well as
allowing a single asterisk   (*)   to be used for a date   (which signifies that the current date is to be used).

The dates may be specified in the following formats:

       ,            (a comma)        indicates today's date
       *            (an asterisk)    indicates today's date 
       yyyy-mm-dd   where yyyy may be a 2- or 4-digit year, mm may be a 1- or 2-digit month, dd may be a 1- or 2-digit day of month
       mm/dd/yyyy   (as above)
       mm/dd        (as above),  but the current year is assumed
       dd\mm\yyyy   (as above)
       dd\mm        (as above),  but the current year is assumed



Commas   (,)   are inserted into numbers where appropriate.

Also, more informative error messages are generated.

/*REXX program computes the number of days between two dates in the form of  YYYY-MM-DD */
parse arg $.1 $.2 _ . 1 . . xtra /*obtain two arguments from the C.L. */
seps= '/-\'; yr.= .; mon.= .; dd.= . /*define the defaults for both dates. */
do a=1 for 2 /*process both of the specified dates. */
if $.a=='' | $.a=="*" | $.a==',' then $.a= date("I")
do s=1 for length(seps) /*process a specified date by separator*/
sep= substr(seps, s, 1) /*obtain one of the supported sep char.*/
if pos(sep, $.a)\==0 then call conv $.a /*parse the date string.*/
end /*s*/
end /*a*/
?.1= '1st'
?.2= '2nd'
if _ \== '' then call err "too many arguments specified: " xtra
dy.= 31 /*default number of days for all months*/
parse value 30 with dy.4 1 dy.6 1 dy.9 1 dy.11 /*define 30─day months, Feb. is special*/
@notCorr= "isn't in a support date format: " /*used for a literal for an error msg. */
 
do j=1 for 2 /*examine both dates for correct format*/
if $.j =='' then call err ?.j "date was not specified."
if length(yr.j)==0 then call err ?.j "year" @notCorr '(missing)'
if isDec(yr.j) then call err ?.j "year" @notCorr '(has a non─decimal digit)'
if yr.j<1 | yr.j>9999 then call err ?.j "year" @notCorr '(not in the range 1──►9999)'
if length(mon.j)==0 then call err ?.j "month" @notCorr '(missing)'
if isDec(mon.j) then call err ?.j "month" @notCorr '(has a non─decimal digit)'
if mon.j<1 | mon.j>12 then call err ?.j "month" @notCorr '(not in the range 1──►12)'
if length(dd.j)==0 then call err ?.j "day" @notCorr '(missing)'
if isDec(dd.j) then call err ?.j "day" @notCorr '(has a non─decimal digit)'
mo= mon.j
if leapYr(yr.j) then dy.2= 29 /*Is it a leapyear? Use 29 days for Feb*/
else dy.2= 28 /*Isn't " " " 28 " " " */
if dd.j<1 | dd.j>dy.mo then call err ?.j "day" @notCorr '(day in month is invalid)'
 
yr.j= right( yr.j +0, 4, 0) /*force YYYY to be four decimal digits.*/
mon.j= right(mon.j +0, 2, 0) /* " MON " " two " " */
dd.j= right( dd.j +0, 2, 0) /* " DD " " " " " */
$.j= yr.j'-'mon.j"-"dd.j /*reconstitute a date from above parts.*/
end /*j*/
 
between= abs( date('B', $.1, "I") - date('B', $.2, "I") ) /* # days between dates.*/
parse source . how . /*determine how invoked.*/
if how='COMMAND' then say commas(between) ' days between ' $.1 " and " $.2
exit between /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
commas: parse arg _; do c_=length(_)-3 to 1 by -3; _=insert(',', _, c_); end; return _
err: say; say '***error*** ' arg(1); exit 13 /*issue an error message (with text) */
isDec: return verify( arg(1), 1234567890) \== 0 /*insure argument is just decimal digs.*/
leapYr: arg _; ly=_//4==0; if ly==0 then return 0; ly=((_//100\==0)|_//400==0); return ly
serDAT: call err 'illegal date format with a separator= ['sep"], date= " @dat
/*──────────────────────────────────────────────────────────────────────────────────────*/
conv: parse arg @dat /*obtain date that the user specified. */
if sep=='-' then parse var @dat yr.a "-" mon.a '-' dd.a /* yy-mm-dd */
if sep=='/' then parse var @dat mon.a "/" dd.a '/' yr.a /* mm/dd/yy */
if sep=='\' then parse var @dat dd.a "\" mon.a '\' yr.a /* dd\mm\yy */
if yr.a=='' then yr.a= right( date(), 4) /*omitted yy*/
if length(yr.a)==2 then yr.a= left( date('S'), 2)yr.a /*2 dig yy ?*/
if yr.a==. | mon.a==. | dd.a==. then call serDAT /*validate. */
return
output   when using the inputs of:     *   2000-1-1

Today   (indicated by the asterisk)   is   2019-10-2

7,214  days between  2019-10-02  and  2000-01-01

Ring[edit]

 
load "stdlib.ring"
 
DaysBetween = [["1995-11-21","1995-11-21"],
["2019-01-01","2019-01-02"],
["2019-01-02","2019-01-01"],
["2019-01-01","2019-03-01"],
["2020-01-01","2020-03-01"],
["1902-01-01","1968-12-25"],
["2090-01-01","2098-12-25"]]
 
for n = 1 to len(DaysBetween)
date1 = DaysBetween[n][1]
date2 = DaysBetween[n][2]
date3 = substr(date1,9,2) + "/" + substr(date1,6,2) + "/" + substr(date1,1,4)
date4 = substr(date2,9,2) + "/" + substr(date2,6,2) + "/" + substr(date2,1,4)
 ? "Days between " + DaysBetween[n][1] + " and " + DaysBetween[n][2] + ": " + diffdays(date4,date3)
next
 
Output:
Days between 1995-11-21 and 1995-11-21: 0
Days between 2019-01-01 and 2019-01-02: 1
Days between 2019-01-02 and 2019-01-01: -1
Days between 2019-01-01 and 2019-03-01: 59
Days between 2020-01-01 and 2020-03-01: 60
Days between 1902-01-01 and 1968-12-25: 0
Days between 2090-01-01 and 2098-12-25: 3280

Ruby[edit]

require "date"
 
d1, d2 = Date.parse("2019-1-1"), Date.parse("2019-10-19")
 
p (d1 - d2).to_i # => -291
p (d2 - d1).to_i # => 291
 

Rust[edit]

// [dependencies]
// chrono = "0.4"
 
use chrono::NaiveDate;
 
fn main() {
let args: Vec<String> = std::env::args().collect();
if args.len() != 3 {
eprintln!("usage: {} start-date end-date", args[0]);
std::process::exit(1);
}
if let Ok(start_date) = NaiveDate::parse_from_str(&args[1], "%F") {
if let Ok(end_date) = NaiveDate::parse_from_str(&args[2], "%F") {
let d = end_date.signed_duration_since(start_date);
println!("{}", d.num_days());
} else {
eprintln!("Can't parse end date");
std::process::exit(1);
}
} else {
eprintln!("Can't parse start date");
std::process::exit(1);
}
}
Output:
days_between_dates 2020-01-01 2020-09-06
249

Scala[edit]

object DaysBetweenDates {
 
/*Inspired by the Python version of the algorithm and the discussion here
https://stackoverflow.com/questions/12862226/the-implementation-of-calculating-the-number-of-days-between-2-dates.*/

 
/**Transform a date into a day number in the Gregorian Calendar*/
def dateToDays(year : Int, month : Int, day : Int ) : Int = {
val m = (month+ 9) % 12
val y = year - m/10
val d = day
365*y + y/4 - y/100 + y/400 + (m*306 + 5)/10 + (d - 1)
}
 
/**Compute the difference of days between both input dates*/
def daysDifference(firstDate : String, secondDate : String) : Int = {
val firstDateTuple = firstDate.split('-') match { case Array(a, b, c) => (a, b, c) }
val secondDateTuple = secondDate.split('-') match { case Array(a, b, c) => (a, b, c) }
 
val firstYear = dateToDays( firstDateTuple._1.toInt, firstDateTuple._2.toInt, firstDateTuple._3.toInt)
val secondYear = dateToDays( secondDateTuple._1.toInt, secondDateTuple._2.toInt, secondDateTuple._3.toInt )
 
return secondYear - firstYear
}
 
def main(args: Array[String]): Unit = {
println(daysDifference("2019-01-01", "2019-09-30"))
println(daysDifference("1995-11-21", "1995-11-21"))
println(daysDifference("2019-01-01", "2019-01-02"))
println(daysDifference("2019-01-02", "2019-01-01"))
println(daysDifference("2019-01-01", "2019-03-01"))
println(daysDifference("2020-01-01", "2020-03-01"))
println(daysDifference("1902-01-01", "1968-12-25"))
println(daysDifference("2090-01-01", "2098-12-25"))
println(daysDifference("1902-01-01", "2098-12-25"))
}
 
}
 
Output:
272
0
1
-1
59
60
24465
3280
71947

Sidef[edit]

require('Date::Calc')
 
func days_diff(a,b) {
%S<Date::Calc>.Delta_Days(a.split('-')..., b.split('-')...)
}
 
var date1 = "1970-01-01"
var date2 = "2019-10-02"
 
say "Date 1: #{date1}"
say "Date 2: #{date2}"
 
var days = days_diff(date1, date2)
 
say "There are #{days} days between these dates"
Output:
Date 1: 1970-01-01
Date 2: 2019-10-02
There are 18171 days between these dates

Swift[edit]

import Foundation
 
func daysFromTimeInterval(_ interval: Double) -> Int {
return Int(interval) / 86400
}
 
let formatter = DateFormatter()
 
formatter.dateFormat = "yyyy-MM-dd"
 
print("Enter date one (yyyy-MM-dd): ", terminator: "")
 
guard let date1Str = readLine(strippingNewline: true), let date1 = formatter.date(from: date1Str) else {
fatalError("Invalid date two")
}
 
print("Enter date two (yyyy-MM-dd): ", terminator: "")
 
guard let date2Str = readLine(strippingNewline: true), let date2 = formatter.date(from: date2Str) else {
fatalError("Invalid date two")
}
 
let (start, end) = date1 > date2 ? (date2, date1) : (date1, date2)
let days = daysFromTimeInterval(DateInterval(start: start, end: end).duration)
 
print("There are \(days) days between \(start) and \(end)")
Output:
Enter date one (yyyy-MM-dd): 2019-01-01
Enter date two (yyyy-MM-dd): 2019-12-02
There are 335 days between 2019-01-01 05:00:00 +0000 and 2019-12-02 05:00:00 +0000

UNIX Shell[edit]

Works with: Bourne Again Shell
# return true if year is leap in Gregorian calendar
leap() {
local -i year
year=$1
if (( year % 4 )); then return 1; fi
if (( year % 100 )); then return 0; fi
! (( year % 400 ))
}
 
# convert date to Gregorian day count (Rata Die), where RD 1 = January 1, 1 CE
rd() {
local year month day
IFS=- read year month day <<<"$1"
local -i elapsed_years=year-1
(( day += elapsed_years * 365 ))
(( day += elapsed_years/4 ))
(( day -= elapsed_years/100 ))
(( day += elapsed_years/400 ))
local month_lengths=(31 28 31 30 31 30 31 31 30 31 30 31)
if leap "$year"; then let month_lengths[1]+=1; fi
local m
for (( m=0; m<month-1; ++m)); do
(( day += month_lengths[m] ))
done
printf '%d\n' "$day"
}
 
days_between() {
local -i date1 date2
date1=$(rd "$1")
date2=$(rd "$2")
printf '%d\n' $(( date2 - date1 ))
}
 
days_between 1970-01-01 2019-12-04
 
Output:
18234

Visual Basic .NET[edit]

Translation of: C#
Imports System.Globalization
 
Module Module1
 
Function DateDiff(d1 As String, d2 As String) As Integer
Dim a = DateTime.ParseExact(d1, "yyyy-MM-dd", CultureInfo.InvariantCulture)
Dim b = DateTime.ParseExact(d2, "yyyy-MM-dd", CultureInfo.InvariantCulture)
Return (b - a).TotalDays
End Function
 
Sub Main()
Console.WriteLine(DateDiff("1970-01-01", "2019-10-18"))
End Sub
 
End Module
Output:
18187

Wren[edit]

Library: Wren-date
import "/date" for Date
 
var datePairs = [
["1995-11-21", "1995-11-21"],
["2019-01-01", "2019-01-02"],
["2019-01-02", "2019-01-01"],
["2019-01-01", "2019-03-01"],
["2020-01-01", "2020-03-01"],
["1902-01-01", "1968-12-25"],
["2090-01-01", "2098-12-25"],
["1902-01-01", "2098-12-25"],
["1970-01-01", "2019-10-18"],
["2019-03-29", "2029-03-29"],
["2020-02-29", "2020-03-01"]
]
for (dates in datePairs) {
var date1 = Date.parse(dates[0])
var date2 = Date.parse(dates[1])
var days = (date2 - date1).days
Date.default = Date.isoDate
System.print("Days between %(date1) and %(date2) = %(days)")
}
Output:
Days between 1995-11-21 and 1995-11-21 = 0
Days between 2019-01-01 and 2019-01-02 = 1
Days between 2019-01-02 and 2019-01-01 = -1
Days between 2019-01-01 and 2019-03-01 = 59
Days between 2020-01-01 and 2020-03-01 = 60
Days between 1902-01-01 and 1968-12-25 = 24465
Days between 2090-01-01 and 2098-12-25 = 3280
Days between 1902-01-01 and 2098-12-25 = 71947
Days between 1970-01-01 and 2019-10-18 = 18187
Days between 2019-03-29 and 2029-03-29 = 3653
Days between 2020-02-29 and 2020-03-01 = 1

zkl[edit]

var [const] TD=Time.Date;
today:=TD.parseDate("--"); // "yyyy-mm-dd" and variations --> (y,m,d)
// or Time.Clock.UTC --> (y,m,d,h,m,s)
then:=TD.parseDate("2018-9-30");
diff:=TD.deltaDays(then,today.xplode()); // ( (y,m,d), y,m,d )
println("Number of days between %s and %s: %d".fmt(then,today,diff));
println("Number of days between %s and %s: %d".fmt(
TD.toYMDString(today.xplode()), // to(y,m,d) not to((y,m,d))
TD.toYMDString(then.xplode()),
TD.deltaDays(today,then.xplode())));
Output:
Number of days between L(2018,9,30) and L(2019,9,30): 365
Number of days between 2019-09-30 and 2018-09-30: -365