已知第几周 获取此周的日期

 $dateString="2021-6周"

 $dates = date_create();
 $years = substr($dateString, 0, 4);
 $weeks = substr($dateString, 5, 2);
 date_isodate_set($dates, $years, $weeks);
 $start = date_format($dates, "Y-m-d");