PHP获取日期时间差

PHP中我们常使用DateTime对象来获取日期和时间。那么如果我们想要求两个时间差呢？

一种办法显然是使用mktime()函数来获取两个日期或时间的Unix Timestamp，再求出两者的差，最后将Unix Stamp转化为时间：

//2017-03-31 14:25:00
$datetime_1 = mktime(14, 25, 0, 3, 31, 2017);
$now = mktime();

//$date_diff now contains the difference in seconds between //$datetime1 and $now
$date_diff = $now - $datetime_1;

而另外一种更方便的方法就是使用DataTime的diff函数：

//current time based on local machine's time zone setting
$datetime1 = new DateTime();

//2017-05-12 14:25:00
$datetime2  = new DateTime("2017-05-12 14:25:00");

//获取$datetime2 - $datetime1的时间差
$timediff = $datetime1->diff($datetime2);

注意：$datetime1->diff($datetime2)所返回的是一个DateInterval对象：

DateInterval {
    /* Properties */
    public integer $y ;
    public integer $m ;
    public integer $d ;
    public integer $h ;
    public integer $i ;
    public integer $s ;
    public integer $invert ;
    public mixed $days ;

    /* Methods */
    public __construct ( string $interval_spec )
    public static DateInterval createFromDateString ( string $time )
    public string format ( string $format )
}

若是获取的时间差为负，那么其中$invert的值为1，若为正，则$invert为0。而我们可以很方便地得到时间差：

//小时数差
$hourdiff = $timediff->h;
//分钟数差
$minutediff = $timediff->i;
//年份差
$yeardiff = $timediff->y;
...

另外DateInterval有一个很好用的函数format()：

//将会以xx:xx的形式输出时间差（比如05:21，即相差5小时21分钟）
echo $timediff->format('%H:%I');

这样大大方便了输出的可读性。具体的format()函数格式如下：

Format Character	Description	Example values
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	-,