如何在 PHP 中確定一個月內某一天的周數？

How to Determine the Week Number of a Day Within a Month in PHP

Determining the week number of a specific day within a month can be a challenging task. This article provides a detailed solution to this problem in PHP, allowing you to easily identify the week number for any given date.

Solution:

The provided PHP function, getWeeks(), calculates the number of weeks into the month for a specified date. It takes two parameters:

• $date: The date in YYYY-MM-DD format.
• $rollover: The day on which the week rolls over (e.g., "sunday" or "monday").

The function works by first extracting the year and month from the date and calculating the number of days between the specified date and the first day of the month. It then iterates through the days of the month, checking if each day falls on the specified rollover day. If so, it increments the week count.

Example Usage:

<?php

    /**
     * Returns the amount of weeks into the month a date is
     * @param $date a YYYY-MM-DD formatted date
     * @param $rollover The day on which the week rolls over
     */
    function getWeeks($date, $rollover)
    {
        $cut = substr($date, 0, 8);
        $daylen = 86400;

        $timestamp = strtotime($date);
        $first = strtotime($cut . "00");
        $elapsed = ($timestamp - $first) / $daylen;

        $weeks = 1;

        for ($i = 1; $i <= $elapsed; $i++)
        {
            $dayfind = $cut . (strlen($i) < 2 ? '0' . $i : $i);
            $daytimestamp = strtotime($dayfind);

            $day = strtolower(date("l", $daytimestamp));

            if($day == strtolower($rollover))  $weeks ++;
        }

        return $weeks;
    }


    //
    echo getWeeks("2011-06-11", "sunday"); //outputs 2, for the second week of the month
?>

Explanation:

The example above calls the getWeeks() function with the date "2011-06-11" and the rollover day "sunday". The result is 2, indicating that June 11, 2011 falls in the second week of June for a rollover on Sunday.

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