PHP 时间换算

<?php
date_default_timezone_set ('Asia/Shanghai');
//echo ' '.date_default_timezone_get ();
echo ' '.date("Y-n-d H-i-s");

$startDate = "2010-06-15 11:49:00";//开始时间
$endDate = "2010-05-05 12:53:00";//结束时间

echo ' //相差的天数';
echo ' '.$startDate.'与'.$endDate.'相差'.abs((strtotime($startDate) - strtotime($endDate)))/(24*3600).'天' ;
echo ' 相差的小时';
echo ' '.$startDate.'与'.$endDate.'相差'.abs((strtotime($startDate) - strtotime($endDate)))/(24*3600)*(24).'小时' ;
echo ' 相差的分钟';
echo ' '.$startDate.'与'.$endDate.'相差'.abs((strtotime($startDate) - strtotime($endDate)))/(24*3600)*24*(60).'分钟' ;
echo ' 相差的秒';
echo ' '.$startDate.'与'.$endDate.'相差'.abs((strtotime($startDate) - strtotime($endDate)))/(24*3600)*24*60*(60).'秒' ;
echo ' 判断一天是星期几';
echo ' '.$startDate.'是星期'.date("w",strtotime($startDate));

echo ' //获取某年的第几周的起始和结束日期';
function getWeekDate($week,$year)
{
 $timestamp = mktime(0,0,0,1,1,$year);
 $dayofweek = date("w",$timestamp);
 if( $week != 1)
 $distance = ($week-1)*7-$dayofweek+1;
 $passed_seconds = $distance * 86400;
 $timestamp += $passed_seconds;
 $firt_date_of_week = date("Y-m-d",$timestamp);
 if($week == 1)
 $distance = 7-$dayofweek;
 else
 $distance = 6;
 $timestamp += $distance * 86400;
 $last_date_of_week = date("Y-m-d",$timestamp);
 return array($firt_date_of_week,$last_date_of_week);
}
$weekDate = getWeekDate(3,date('Y',strtotime($startDate)));
echo ' '.$startDate.'第3个星期起止日期'.$weekDate[0].' 至 '.$weekDate[1];

$startTime = strtotime($startDate);
$endTime = strtotime($endDate);

$time = abs($startTime-$endTime);
$start = 0;
$string = "两个时间相差：";
$y = floor($time/(3600*24*360));
echo ' 年:'.$y;
if($start || $y )
{
 $start = 1;
 $time -= $y*3600*24*360;
 $string .= $y."年";
}
$m = floor($time/(3600*24*31));
echo ' 月:'.$m;
if($start || $m)
{
 $start = 1;
 $time -= $m*3600*24*31;
 $string .= $m."月";
}
$d = floor($time/(3600*24));
echo ' 天:'.$d;
if($start || $d)
{
 $start = 1;
 $time -= $d*3600*24;
 $string .= $d."天";
}
$h = floor($time/(3600));
echo ' 小时:'.$h;
if($start || $h)
{
 $start = 1;
 $time -= $h*3600;
 $string .= $h."时";
}
$s = floor($time/(60));
echo ' 分:'.$s;
if($start || $s)
{
 $start = 1;
 $time -= $s*60;
 $string .= $s."分";
}
echo ' 秒:'.$time.' ';

$string .= "{$time}秒";
echo $string;
?>

以下补充一些:
date_default_timezone_set('PRC'); //默认时区
echo "今天:",date("Y-m-d",time())," ";
echo "今天:",date("Y-m-d",strtotime("18 june 2008"))," ";
echo "昨天:",date("Y-m-d",strtotime("-1 day")), " ";
echo "明天:",date("Y-m-d",strtotime("+1 day")), " ";
echo "一周后:",date("Y-m-d",strtotime("+1 week")), " ";
echo "一周零两天四小时两秒后:",date("Y-m-d G:H:s",strtotime("+1 week 2 days 4 hours 2 seconds")), " ";
echo "下个星期四:",date("Y-m-d",strtotime("next Thursday")), " ";
echo "上个周一:".date("Y-m-d",strtotime("last Monday"))." ";
echo "一个月前:".date("Y-m-d",strtotime("last month"))." ";
echo "一个月后:".date("Y-m-d",strtotime("+1 month"))." ";
echo "十年后:".date("Y-m-d",strtotime("+10 year"))." ";

如何实现加一个月

echo date("Y-m-d",strtotime("+1months",strtotime("2011-08-04"))); //结果是 2011-09-04

一周，改成 +1week