方式一：

     diff($datetime2)->format('%R%a'));}echo days(2015,1)."
";echo days(2015,2)."
";echo days(2015,3)."
";echo days(2015,4)."
";echo days(2015,5)."
";echo days(2015,6)."
";echo days(2015,7)."
";echo days(2015,8)."
";echo days(2015,9)."
";echo days(2015,10)."
";echo days(2015,11)."
";echo days(2015,12)."
";echo days(2016,1)."
";echo days(2015,12)."
";

方式二：

方式三：

 

//date('m/d/y', strtotime('first day')); # 02/01/10//date('m/d/y', strtotime('last day')); # 02/28/10//date('m/d/y', strtotime('last day next month')); # 03/31/10//date('m/d/y', strtotime('last day last month')); # 01/31/10date('m/d/y', strtotime('first day')); # 02/01/10date('m/d/y', strtotime('first day next month')); # 03/01/10

 

方式四：

$i=12;$y=2015;echo date("t",strtotime("$y-$i"));