DateTime::format()

DateTimeImmutable::format

DateTimeInterface::format

date_format

(PHP 5 >= 5.2.1, PHP 7)

Returns date formatted according to given format

说明

面向对象风格
publicDateTime::format(string $format): string

publicDateTimeImmutable::format(string $format): string

publicDateTimeInterface::format(string $format): string

过程化风格
date_format(DateTimeInterface$object,string $format): string

Returns date formatted according to given format.

参数

$object

仅为过程化风格：由date_create()返回的DateTime类型的对象。

$format

Format accepted bydate().

返回值

Returns the formatted date string on success 或者在失败时返回FALSE.

范例

Example #1DateTime::format()example

面向对象风格

<?php
$date = new DateTime('2000-01-01');
echo $date->format('Y-m-d H:i:s');
?>

过程化风格

<?php
$date = date_create('2000-01-01');
echo date_format($date, 'Y-m-d H:i:s');
?>

以上例程会输出：

2000-01-01 00:00:00

注释

This method does not use locales. All output is in English.

参见

• date() 格式化一个本地时间／日期

Using a datetime field from a mysql database e.g. "2012-03-24 17:45:12"
<?php
$result = mysql_query("SELECT `datetime` FROM `table`");
$row = mysql_fetch_row($result);
$date = date_create($row[0]);
echo date_format($date, 'Y-m-d H:i:s');
#output: 2012-03-24 17:45:12
echo date_format($date, 'd/m/Y H:i:s');
#output: 24/03/2012 17:45:12
echo date_format($date, 'd/m/y');
#output: 24/03/12
echo date_format($date, 'g:i A');
#output: 5:45 PM
echo date_format($date, 'G:ia');
#output: 05:45pm
echo date_format($date, 'g:ia \o\n l jS F Y');
#output: 5:45pm on Saturday 24th March 2012
?>

For full reference of the supported format character and results,
see the documentation of date() :
http://www.php.net/manual/en/function.date.php

Seems like datetime::format does not really support microseconds as the documentation under date suggest it will.
Here is some code to generate a datetime with microseconds and timezone:
private function udate($format = 'u', $utimestamp = null) {
    if (is_null($utimestamp))
      $utimestamp = microtime(true);
    $timestamp = floor($utimestamp);
    $milliseconds = round(($utimestamp - $timestamp) * 1000000);
    return date(preg_replace('`(?<!\\\\)u`', $milliseconds, $format), $timestamp);
  }
echo udate('Y-m-d H:i:s.u T');
// Will output something like: 2014-01-01 12:20:24.42342 CET

There is a bit confusing logic may appear using year week number:
<?php
echo (new \DateTime("2018-12-31 13:05:21"))->format("YW") . PHP_EOL;
?>
will output 201801, not 201901 nor 201852, because of strange ISO_8601-2004 standard: the first calendar week of a year is that one which includes the first Thursday of that year, so this date (it is Monday) do belong to the first week of 2019 (this is why 'W' format gives 01), but internal timestamp is of 2018 (and 'Y' format obey this), therefore getting us unexpected result of 201801. So be careful when using this output with something important (i know projects where this was used to form MySQL partitions).

The date_format can be use to get the last day of February:
<?php 
function last_day_of_feb ($year) {
# The 0th day of a month is the same as the last day of the month before
    $ultimo_feb_str = $year . "-03-00"; 
    $ultimo_feb_date = date_create($ultimo_feb_str);
    $return = date_format($ultimo_feb_date, "Y-m-d");
    return $return;
}
echo last_day_of_feb(2011) . "\n"; # 2011-02-28
echo last_day_of_feb(2012) . "\n"; # 2011-02-29
?>

The udate function is a great start, but the formatting of the milliseconds is a little off. If it is within the first 100000 microseconds then the string will be less than 6 characters, so 0.012435 will appear as 0.12345. The revision below fixes this.
function udate($strFormat = 'u', $uTimeStamp = null)
{
  // If the time wasn't provided then fill it in
  if (is_null($uTimeStamp))
  {
    $uTimeStamp = microtime(true);
  }
  // Round the time down to the second
  $dtTimeStamp = floor($uTimeStamp);
  // Determine the millisecond value
  $intMilliseconds = round(($uTimeStamp - $dtTimeStamp) * 1000000);
  // Format the milliseconds as a 6 character string
  $strMilliseconds = str_pad($intMilliseconds, 6, '0', STR_PAD_LEFT);
  // Replace the milliseconds in the date format string
  // Then use the date function to process the rest of the string
  return date(preg_replace('`(?<!\\\\)u`', $strMilliseconds, $strFormat), $dtTimeStamp);
}

$saved_time="2019-03-09 14:25:20";
  $formated_saved_time = new DateTime($saved_time);
  $current_time = new DateTime();
  $interval = $current_time->diff($formated_saved_time);
 
   if (!empty($interval->format('%a'))){
    $time_difference=$interval->format('%a days ago');
    } elseif ($formated_saved_time->format('d') != $current_time->format('d')){
       $time_difference="yesterday";
       }elseif (!empty($interval->format('%h'))){
           $time_difference=$interval->format('%h hr, %i min ago');
           } elseif (!empty($interval->format('%i'))){
               $time_difference=$interval->format('%i min ago');
               } elseif (!empty($interval->format('%s'))){
                $time_difference=$interval->format('%s sec ago');
 } 
output ----- posted 4 hr, 12 min ago at 2019-03-09 14:25:20
see the code in action here 
https://eval.in/1081921

I believe this is a bug but its note-worthy if it is intended (I am using PHP 5.5.3).
$ php --version
PHP Warning: Module 'xdebug' already loaded in Unknown on line 0
PHP 5.5.3-1ubuntu2.1 (cli) (built: Dec 12 2013 04:24:35) 
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2013 Zend Technologies
  with Xdebug v2.2.3, Copyright (c) 2002-2013, by Derick Rethans
  with Zend OPcache v7.0.3-dev, Copyright (c) 1999-2013, by Zend Technologies
What is happening:
DateTime() >format() will modify the timezone. So do not expect the public date property to be returned (format mask applied) based on the current public timezone property. format will decide that when calling ->format() it will use the server timezone which eliminates all usefulness of ->setTimezone().
<?php
      $nowUtc = new \DateTime( 'now', new \DateTimeZone( 'UTC' ) );
      echo '$nowUtc'.PHP_EOL;
      var_dump($nowUtc);
      $nowUtc = new \DateTime( 'now', new \DateTimeZone( 'UTC' ) );
      echo '$nowUtc->format(\'Y-m-d h:i:s\')'.PHP_EOL;
      var_dump($nowUtc->format('Y-m-d h:i:s'));
      $nowUtc->setTimezone( new \DateTimeZone( 'Australia/Sydney' ) );
      echo '$nowUtc->setTimezone( new \DateTimeZone( \'Australia/Sydney\' ) )'.PHP_EOL;
      var_dump($nowUtc);
      echo '$nowUtc->format(\'Y-m-d h:i:s\')'.PHP_EOL;
      var_dump($nowUtc->format('Y-m-d h:i:s'));exit;
?>
outputs;
$nowUtc
object(DateTime)[2607]
 public 'date' => string '2014-02-13 02:42:48' (length=19)
 public 'timezone_type' => int 3
 public 'timezone' => string 'UTC' (length=3)
$nowUtc->format('Y-m-d h:i:s')
string '2014-02-13 02:42:48' (length=19)
$nowUtc->setTimezone( new \DateTimeZone( 'Australia/Sydney' ) )
object(DateTime)[2608]
 public 'date' => string '2014-02-13 13:42:48' (length=19)
 public 'timezone_type' => int 3
 public 'timezone' => string 'Australia/Sydney' (length=16)
$nowUtc->format('Y-m-d h:i:s')
string '2014-02-13 01:42:48' (length=19) // expected 2014-02-13 13:42:48 based on Australia/Sydney - what is 2014-02-13 01:42:48 from anyway!