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：

The following characters are recognized in the `format` parameter string. Each format character must be prefixed by a percent sign (%).
`format`character	Description	Example values
%	Literal %	%
Y	Years, numeric, at least 2 digits with leading 0	01, 03
y	Years, numeric	1, 3
M	Months, numeric, at least 2 digits with leading 0	01, 03, 12
m	Months, numeric	1, 3, 12
D	Days, numeric, at least 2 digits with leading 0	01, 03, 31
d	Days, numeric	1, 3, 31
a	Total number of days as a result of a DateTime::diff() or (unknown)otherwise	4, 18, 8123
H	Hours, numeric, at least 2 digits with leading 0	01, 03, 23
h	Hours, numeric	1, 3, 23
I	Minutes, numeric, at least 2 digits with leading 0	01, 03, 59
i	Minutes, numeric	1, 3, 59
S	Seconds, numeric, at least 2 digits with leading 0	01, 03, 57
s	Seconds, numeric	1, 3, 57
R	Sign "-" when negative, "+" when positive	-, +
r	Sign "-" when negative, empty when positive	-,