php将日期函数与周回归0？

Question

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') http://us3.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?

Answer 1

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:

• http://git.php.net/?p=php-src.git;a=blob;f=ext/date/php_date.c
• http://git.php.net/?p=php-src.git;a=blob;f=ext/date/lib/dow.c

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