php中DateTime、diff

手册地址：http://php.net/manual/en/dateinterval.format.php

 1 $january = new DateTime(‘2010-01-01‘);
 2 $february = new DateTime(‘2010-02-01‘);
 3 $interval = $january->diff($february);
 4
 5 // %a will output the total number of days.
 6 echo $interval->format(‘%R%a total days‘). ‘<br/>‘;// +31 total days
 7
 8 // While %d will only output the number of days not already covered by the
 9 // month.
10 echo $interval->format(‘%m month, %d days‘);// 1 month, 0 days

format格式化参数：