datetime format

PHP
<?php
// Assuming today is March 10th, 2001, 5:16:18 pm, and that we are in the
// Mountain Standard Time (MST) Time Zone
//
$today = date("F j, Y, g:i a");                 // March 10, 2001, 5:16 pm
$today = date("m.d.y");                         // 03.10.01
$today = date("j, n, Y");                       // 10, 3, 2001
$today = date("Ymd");                           // 20010310
$today = date('h-i-s, j-m-y, it is w Day');     // 05-16-18, 10-03-01, 1631 1618 6 Satpm01
$today = date('\i\t \i\s \t\h\e jS \d\a\y.');   // it is the 10th day.
$today = date("D M j G:i:s T Y");               // Sat Mar 10 17:16:18 MST 2001
$today = date('H:m:s \m \i\s\ \m\o\n\t\h');     // 17:03:18 m is month
$today = date("H:i:s");                         // 17:16:18
$today = date("Y-m-d H:i:s");                   // 2001-03-10 17:16:18 (the MySQL DATETIME format)
?>
  
/*d	Day of the month, 2 digits with leading zeros	01 to 31
D	A textual representation of a day, three letters	Mon through Sun
j	Day of the month without leading zeros	1 to 31
l (lowercase 'L')	A full textual representation of the day of the week	Sunday through Saturday
N	ISO-8601 numeric representation of the day of the week (added in PHP 5.1.0)	1 (for Monday) through 7 (for Sunday)
S	English ordinal suffix for the day of the month, 2 characters	st, nd, rd or th. Works well with j
w	Numeric representation of the day of the week	0 (for Sunday) through 6 (for Saturday)
z	The day of the year (starting from 0)	0 through 365
Week	---	---
W	ISO-8601 week number of year, weeks starting on Monday	Example: 42 (the 42nd week in the year)
Month	---	---
F	A full textual representation of a month, such as January or March	January through December
m	Numeric representation of a month, with leading zeros	01 through 12
M	A short textual representation of a month, three letters	Jan through Dec
n	Numeric representation of a month, without leading zeros	1 through 12
t	Number of days in the given month	28 through 31
Year	---	---
L	Whether it's a leap year	1 if it is a leap year, 0 otherwise.
o	ISO-8601 week-numbering year. This has the same value as Y, except that if the ISO week number (W) belongs to the previous or next year, that year is used instead. (added in PHP 5.1.0)	Examples: 1999 or 2003
Y	A full numeric representation of a year, 4 digits	Examples: 1999 or 2003
y	A two digit representation of a year	Examples: 99 or 03
Time	---	---
a	Lowercase Ante meridiem and Post meridiem	am or pm
A	Uppercase Ante meridiem and Post meridiem	AM or PM
B	Swatch Internet time	000 through 999
g	12-hour format of an hour without leading zeros	1 through 12
G	24-hour format of an hour without leading zeros	0 through 23
h	12-hour format of an hour with leading zeros	01 through 12
H	24-hour format of an hour with leading zeros	00 through 23
i	Minutes with leading zeros	00 to 59
s	Seconds with leading zeros	00 through 59
u	Microseconds (added in PHP 5.2.2). Note that date() will always generate 000000 since it takes an integer parameter, whereas DateTime::format() does support microseconds if DateTime was created with microseconds.	Example: 654321
v	Milliseconds (added in PHP 7.0.0). Same note applies as for u.	Example: 654
Timezone	---	---
e	Timezone identifier (added in PHP 5.1.0)	Examples: UTC, GMT, Atlantic/Azores
I (capital i)	Whether or not the date is in daylight saving time	1 if Daylight Saving Time, 0 otherwise.
O	Difference to Greenwich time (GMT) without colon between hours and minutes	Example: +0200
P	Difference to Greenwich time (GMT) with colon between hours and minutes (added in PHP 5.1.3)	Example: +02:00
T	Timezone abbreviation	Examples: EST, MDT ...
Z	Timezone offset in seconds. The offset for timezones west of UTC is always negative, and for those east of UTC is always positive.	-43200 through 50400
Full Date/Time	---	---
c	ISO 8601 date (added in PHP 5)	2004-02-12T15:19:21+00:00
r	» RFC 2822 formatted date	Example: Thu, 21 Dec 2000 16:01:07 +0200
U	Seconds since the Unix Epoch (January 1 1970 00:00:00 GMT)	See also time()
*/// create date time 2008-03-09 16:05:07.123
DateTime dt = new DateTime(2008, 3, 9, 16, 5, 7, 123);

String.Format("{0:y yy yyy yyyy}",      dt);  // "8 08 008 2008"   year
String.Format("{0:M MM MMM MMMM}",      dt);  // "3 03 Mar March"  month
String.Format("{0:d dd ddd dddd}",      dt);  // "9 09 Sun Sunday" day
String.Format("{0:h hh H HH}",          dt);  // "4 04 16 16"      hour 12/24
String.Format("{0:m mm}",               dt);  // "5 05"            minute
String.Format("{0:s ss}",               dt);  // "7 07"            second
String.Format("{0:f ff fff ffff}",      dt);  // "1 12 123 1230"   sec.fraction
String.Format("{0:F FF FFF FFFF}",      dt);  // "1 12 123 123"    without zeroes
String.Format("{0:t tt}",               dt);  // "P PM"            A.M. or P.M.
String.Format("{0:z zz zzz}",           dt);  // "-6 -06 -06:00"   time zone

// month/day numbers without/with leading zeroes
String.Format("{0:M/d/yyyy}",           dt);  // "3/9/2008"
String.Format("{0:MM/dd/yyyy}",         dt);  // "03/09/2008"

// day/month names
String.Format("{0:ddd, MMM d, yyyy}",   dt);  // "Sun, Mar 9, 2008"
String.Format("{0:dddd, MMMM d, yyyy}", dt);  // "Sunday, March 9, 2008"

// two/four digit year
String.Format("{0:MM/dd/yy}",           dt);  // "03/09/08"
String.Format("{0:MM/dd/yyyy}",         dt);  // "03/09/2008"DateTime.Now.ToString("MM/dd/yyyy HH:mm:ss")%a - Abbreviated weekday name. (Sun, Mon, ...)
%A - Full weekday name. (Sunday, Monday, ...)
%w - Weekday as a decimal number. (0, 1, ..., 6)
%d - Day of the month as a zero-padded decimal. (01, 02, ..., 31)
%-d - Day of the month as a decimal number. (1, 2, ..., 30)
%b - Abbreviated month name. (Jan, Feb, ..., Dec)
%B - Full month name. (January, February, ...)
%m - Month as a zero-padded decimal number. (01, 02, ..., 12)
%-m - Month as a decimal number. (1, 2, ..., 12)
%y - Year without century as a zero-padded decimal number. (00, 01, ..., 99)
%-y - Year without century as a decimal number. (0, 1, ..., 99)
%Y - Year with century as a decimal number. (2013, 2019 etc.)
%H - Hour (24-hour clock) as a zero-padded decimal number. (00, 01, ..., 23)
%-H - Hour (24-hour clock) as a decimal number. (0, 1, ..., 23)
%I - Hour (12-hour clock) as a zero-padded decimal number. (01, 02, ..., 12)
%-I - Hour (12-hour clock) as a decimal number. (1, 2, ... 12)
%p - Locale’s AM or PM. (AM, PM)
%M - Minute as a zero-padded decimal number. (00, 01, ..., 59)
%-M - Minute as a decimal number. (0, 1, ..., 59)
%S - Second as a zero-padded decimal number. (00, 01, ..., 59)
%-S - Second as a decimal number. (0, 1, ..., 59)
%f - Microsecond as a decimal number, zero-padded on the left.  (000000 - 999999)
%z - UTC offset in the form +HHMM or -HHMM.  
%Z - Time zone name. 
%j - Day of the year as a zero-padded decimal number. (001, 002, ..., 366)
%-j - Day of the year as a decimal number. (1, 2, ..., 366)
%U - Week number of the year (Sunday as the first day of the week). All days in a new year preceding the first Sunday are considered to be in week 0. (00, 01, ..., 53)
%W - Week number of the year (Monday as the first day of the week). All days in a new year preceding the first Monday are considered to be in week 0. (00, 01, ..., 53)
%c - Locale’s appropriate date and time representation. (Mon Sep 30 07:06:05 2013)
%x - Locale’s appropriate date representation. (09/30/13)
%X - Locale’s appropriate time representation. (07:06:05)
%% - A literal '%' character. (%)string labelAttendanceTimestr = DateTime.Now.ToString("HH"+"mm");string foo = yourDateTime.ToUniversalTime()
                         .ToString("yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'fff'Z'");
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