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Editorial Team
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Asked: 2026-06-17T16:55:30+00:00

I came across this conditional in a function I’m working with: <?php $thisweek =

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I came across this conditional in a function I’m working with:

<?php
$thisweek = date('W');
if ($thisweek == 0) {
  // ...
}

I didn’t write this conditional and when I went to look up the range of the date(‘W’) https://www.php.net/manual/en/function.date.php it gives an example but no range like 00-52 or 01-52.

My question is will date(‘W’) ever return zero meeting this conditional?

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1 Answer

  1. Editorial Team

    The PHP date('W') function will never1 return 0.

    Look it up in the source code of PHP, ext/date/php_date.c.

    Slightly formatted around line 950-1000:

    timelib_sll isoweek, isoyear;
int weekYearSet = 0;
...
/* week */
case 'W':
    if(!weekYearSet) {
        timelib_isoweek_from_date(t->y, t->m, t->d, &isoweek, &isoyear);
        weekYearSet = 1;
    }
    length = slprintf(buffer, 32, "%02d", (int) isoweek); break; /* iso weeknr */

    What is timelib_isoweek_from_date? Well… looking at the logic in ext/date/lib/dow.c, from line 82 it can be concluded that the week number varies from 1 to 53:

    /* Find if Y M D falls in YearNumber Y-1, WeekNumber 52 or 53 */
...
/* 8. Find if Y M D falls in YearNumber Y+1, WeekNumber 1 */
...
/* 9. Find if Y M D falls in YearNumber Y, WeekNumber 1 through 53 */

    If you do not believe me, look in the code yourself:

    1) “Never” means “as long as there is no bug in PHP”.

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