PHP：獲取週數由1969年

Question

我需要1969年獲得實際的週數起這樣開始：

$dateTime = new DateTime; 
$now = '2017-01-01'; 

// 
// $week = date('W', strtotime($now . ' +2 days')); 
// I will get the week number between 01-53 and this is not what I want. 
// I need to set the starting year and get the week number since 1969 to get the expected results. 
// How to get the value 2506 from this $week variable? 
// 

$dateTime->setISODate('1969', 2506, -1); 
$start_by = $dateTime->format('Y-m-d'); 

// output: 2016-12-31 

正如你所看到的，「2016年12月31日」是日期時間我的一週開始。

預先感謝您！

Answer 1

看似簡單，

<?php 
    $date1 = new DateTime(); 
    $date2 = new DateTime("1969-01-21"); 
    $interval = $date1->diff($date2); 

    echo ceil($interval->days/7); 
?>