获取一个月中的第一个或最后一个星期五

Question

我正在尝试写一个这样的日历函数

function get_date($month, $year, $week, $day, $direction)
{
    ....
}

$week 是一个整数 (1, 2, 3...)，$day 是一天 (Sun, Mon, ...) 或数字，以更容易的为准。方向有点混乱，因为它做了不同的计算。

举个例子，让我们调用

get_date(5, 2009, 1, 'Sun', 'forward');

它使用默认值，并获取 5 月的第一个星期日，即 2009-05-03。如果我们调用

get_date(5, 2009, 2, 'Sun', 'backward');

，它返回 5 月的倒数第二个星期日，即 2009-05-24。

Answer 1

与语言无关的版本：

要获取该月的第一天，请从该月的第一天开始：yyyy-mm-01。使用任何可用的函数来给出对应于星期几的数字。从您要查找的日期中减去该数字；例如，如果该月的第一天是星期三 (2)，而您正在寻找星期五 (4)，则从 4 中减去 2，留下 2。如果答案是否定的，则添加 7。最后将其添加到第一个这个月;以我为例，第一个星期五是第三个。

要获得该月的最后一个星期五，请找到下个月的第一个星期五并减去 7 天。

Answer 2

也许它可以做得更快...
这对编码非常有趣。

请注意，$direction 是 1 表示前进，-1 表示后退以使事情变得轻松 :)
此外，$day 以 1 为星期一开始，以 7 为星期日结束。

function get_date($month, $year, $week, $day, $direction) {
  if($direction > 0)
    $startday = 1;
  else
    $startday = date('t', mktime(0, 0, 0, $month, 1, $year));

  $start = mktime(0, 0, 0, $month, $startday, $year);
  $weekday = date('N', $start);

  if($direction * $day >= $direction * $weekday)
    $offset = -$direction * 7;
  else
    $offset = 0;

  $offset += $direction * ($week * 7) + ($day - $weekday);
  return mktime(0, 0, 0, $month, $startday + $offset, $year);
}

我已经用几个示例对其进行了测试，并且似乎总是可以正常工作，但请务必仔细检查；）

Answer 3

PHP 的内置时间函数让这一切变得简单。

http://php.net/manual/en/function.strtotime.php

// Get first Friday of next month.
$timestamp = strtotime('first fri of next month');

// Get second to last Friday of the current month.
$timestamp = strtotime('last fri of this month -7 days');

// Format a timestamp as a human-meaningful string.
$formattedDate = date('F j, Y', strtotime('first wed of last month'));

请注意，我们始终希望确保已为 strtotime 定义了正确的时区，以便 PHP 了解在哪里计算相对于机器认为的时区的时间戳。

date_default_timezone_set('America/New_York');
$formattedDate = date('F j, Y', strtotime('first wed of last month +1 week'));

Answer 4

strtotime() 可以帮助你。例如

<?php
$tsFirst = strtotime('2009-04-00 next friday');
$tsLast = strtotime('2009-05-01 last friday');
echo date(DATE_RFC850, $tsFirst), " | ", date(DATE_RFC850, $tsLast);

打印

星期五，2009 年 4 月 3 日 00:00:00 CEST | 2009 年 4 月 24 日星期五 00:00:00 CEST

Answer 5

无需计算或循环 - 使用 strtotime() 很容易做到：

查找特定月份中特定日期的第 N 次或最后一次出现：

/////////////////////////////////////////////////////////////////
// Quick Code
/////////////////////////////////////////////////////////////////

// Convenience mapping.
$Names = array( 0=>"Sun", 1=>"Mon", 2=>"Tue", 3=>"Wed", 4=>"Thu", 5=>"Fri", 6=>"Sat" );

// Specify what we want
// In this example, the Second Monday of Next March
$tsInMonth = strtotime('March');
$Day = 1;
$Ord = 2;

// The actual calculations
$ThisMonthTS = strtotime( date("Y-m-01", $tsInMonth ) );
$NextMonthTS = strtotime( date("Y-m-01", strtotime("next month", $tsInMonth) ) );
$DateOfInterest = (-1 == $Ord) 
    ? strtotime( "last ".$Names[$Day], $NextMonthTS ) 
    : strtotime( $Names[$Day]." + ".($Ord-1)." weeks", $ThisMonthTS ); 


/////////////////////////////////////////////////////////////////
// Explanation
/////////////////////////////////////////////////////////////////

// Specify the month of which we are interested.
// You can use any timestamp inside that month, I'm using strtotime for convenience.
$tsInMonth = strtotime('March');

// The day of interest, ie: Friday.  
// It can be 0=Sunday through 6=Saturday (Like 'w' from date()).
$Day = 5;

// The occurrence of this day in which we are interested.  
// It can be 1, 2, 3, 4 for the first, second, third, and fourth occurrence of the day in question in the month in question.
// You can also use -1 to fine the LAST occurrence.  That will return the fifth occurrence if there is one, else the 4th.
$Ord = 3;

////////////////////////////////////////////////////////////////
// We now have all the specific values we need.
// The example values above specify the 3rd friday of next march
////////////////////////////////////////////////////////////////

// We need the day name that corresponds with our day number to pass to strtotime().
// This isn't really necessary = we could just specify the string in the first place, but for date calcs, you are more likely to have the day number than the string itself, so this is convenient.
$Names = array( 0=>"Sun", 1=>"Mon", 2=>"Tue", 3=>"Wed", 4=>"Thu", 5=>"Fri", 6=>"Sat" );

// Calculate the timestamp at midnight of the first of the month in question.
// Remember $tsInMonth is any date in that month.
$ThisMonthTS = strtotime( date("Y-m-01", $tsInMonth ) );

// Calculate the timestamp at midnight of the first of the FOLLOWING month.
// This will be used if we specify -1 for last occurrence.
$NextMonthTS = strtotime( date("Y-m-01", strtotime("next month", $tsInMonth) ) );

// Now we just format the values a bit and pass them to strtotime().
// To find the 1,2,3,4th occurrence, we work from the first of the month forward.
// For the last (-1) occurence,work we work back from the first occurrence of the following month.
$DateOfInterest = (-1 == $Ord) ?
    strtotime( "last ".$Names[$Day], $NextMonthTS ) : // The last occurrence of the day in this month.  Calculated as "last dayname" from the first of next month, which will be the last one in this month. 
    strtotime( $Names[$Day]." + ".($Ord-1)." weeks", $ThisMonthTS ); // From the first of this month, move to "next dayname" which will be the first occurrence, and then move ahead a week for as many additional occurrences as you need.

Answer 6

echo date('Y-m-d',strtotime('last friday'));

Answer 7

您可以使用mktime 检索当月第一天的unix时间戳：

$firstOfMonth = mktime(0, 0, 0, $month, 1, $year);

如果您有某个月的第一天的日期，则可以使用 date 轻松检索该日期的工作日：

$weekday = date("N", $firstOfMonth);

从那里可以很容易地向前走，得到你想要的日期。

Answer 8

function get_date($month, $year, $week, $day) {
    # $month, $year: current month to search in
    # $week: 0=1st, 1=2nd, 2=3rd, 3=4th, -1=last
    # $day:  0=mon, 1=tue, ..., 6=sun

    $startday=1; $delta=0;
    if ($week < 0) {
        $startday = date('t', mktime(0, 0, 0, $month, 1, $year)); # 28..31
        $delta=1;
    }
    $start  = mktime(0, 0, 0, $month, $startday, $year);
    $dstart = date('w', $start)-1; # last of the month falls on 0=mon,6=sun
    $offset=$day-$dstart; if ($offset<$delta){$offset+=7;}
    $newday=$startday+$offset+($week*7);
    return mktime(0, 0, 0, $month, $newday, $year);
}

这对我有用，并且基于与语言无关的版本:-) 太糟糕了，我需要做那个 delta 的事情（因为如果一个月的最后一天是想要的工作日，我们不需要减去 7）

Answer 9

只要找出有关月份的第一天和最后一天是什么（即 2009 年 5 月 1 日是星期五，2009 年 5 月 31 日是星期日）我相信大多数 PHP 函数使用星期一 = 0，星期日 = 6，因此Friday=4，所以你知道Sunday (6) - Friday (4) = 2，然后31-2 = 29，这意味着这个月的最后一个星期五是29号。第一个星期五，如果为负数，则加7，如果为0，则月份从星期五开始。

Answer 10

使用DateTime 类可以非常优雅地完成相同的操作。

$time_zone = new DateTimeZone('Europe/Ljubljana');

$first_friday_of_this_month = new DateTime('first Friday of this month', $time_zone);
$last_friday_of_this_month = new DateTime('last Friday of this month', $time_zone);

echo $first_friday_of_this_month->format('Y-m-d');  # 2015-11-06
echo $last_friday_of_this_month->format('Y-m-d');  # 2015-11-27

Answer 11

这似乎每次都能完美运行；它采用提供的任何日期并返回该月最后一个星期五的日期，即使是该月的 5 个星期五。

function get_last_friday_of_month($inDate) {
    $inDate = date('Y-m-24', strtotime($inDate));
    $last_friday = date('Y-m-d',strtotime($inDate.' next friday'));
    $next_friday = date('Y-m-d',strtotime($inDate.' next friday'));

    if(date('m', strtotime($last_friday)) === date('m', strtotime($next_friday))){
        $last_friday = $next_friday;
    }else{
        //
    }
    return $last_friday;
}

Answer 12

以下是最快的解决方案，您可以在所有条件下使用。如果你稍微调整一下，你也可以得到一个星期的数组。

function findDate($date, $week, $weekday){
    # $date is the date we are using to get the month and year which should be a datetime object
    # $week can be: 0 for first, 1 for second, 2 for third, 3 for fourth and -1 for last
    # $weekday can be: 1 for Monday, 2 for Tuesday, 3 for Wednesday, 4 for Thursday, 5 for Friday, 6 for Saturday and 7 for Sunday 

    $start = clone $date;
    $finish = clone $date;

    $start->modify('first day of this month');
    $finish->modify('last day of this month');
    $finish->modify('+1 day');

    $interval = DateInterval::createFromDateString('1 day');
    $period = new DatePeriod($start, $interval, $finish);

    foreach($period AS $date){
        $result[$date->format('N')][] = $date;
    }

    if($week == -1)
        return end($result[$weekday]);
    else
        return $result[$weekday][$week];
}


$date = DateTime::createFromFormat('d/m/Y', '25/12/2016');

# find the third Wednesday in December 2016
$result = findDate($date, 2, 3); 
echo $result->format('d/m/Y');

我希望这会有所帮助。

如果您需要任何进一步的信息，请告诉我。 ;)