date_default_timezone_set('PRC'); //默認(rèn)時(shí)區(qū)
//當(dāng)前的時(shí)間增加5天
$date1 = "2018-12-21";
echo date('Y-m-d',strtotime("$date1 +5 day")); //輸出結(jié)果：2018-12-26
//相應(yīng)地,要增加月,年,將day改成month或year即可
//+++ 今天、昨天、明天 、上一周、下一周 +++++++++
echo "今天:",date("Y-m-d",time()),"<hr>";
echo "昨天:",date("Y-m-d",strtotime("-1 day")), "<hr>";
echo "明天:",date("Y-m-d",strtotime("+1 day")), "<hr>";
echo "一周后:",date("Y-m-d",strtotime("+1 week")), "<hr>";
echo "一周零兩天四小時(shí)兩秒后:",date("Y-m-d G:H:s",strtotime("+1 week 2 days 4 hours 2 seconds")), "<hr>";
echo "下個(gè)星期四:",date("Y-m-d",strtotime("next Thursday")), "<hr>";
echo "上個(gè)周一:".date("Y-m-d",strtotime("last Monday"))."<hr>";
echo "一個(gè)月前:".date("Y-m-d",strtotime("last month"))."<hr>";
echo "一個(gè)月后:".date("Y-m-d",strtotime("+1 month"))."<hr>";
echo "十年后:".date("Y-m-d",strtotime("+10 year"))."<hr>";

date_default_timezone_set('PRC'); //默認(rèn)時(shí)區(qū)
/**
* 功能：取得給定日期所在周的開(kāi)始日期和結(jié)束日期
* 參數(shù)：$gdate 日期，默認(rèn)為當(dāng)天，格式：YYYY-MM-DD
* $first 一周以星期一還是星期天開(kāi)始，0為星期天，1為星期一
* 返回：數(shù)組array("開(kāi)始日期", "結(jié)束日期");
*
*/
function aweek($gdate = "", $first = 0){
  if(!$gdate) $gdate = date("Y-m-d");
  $w = date("w", strtotime($gdate));//取得一周的第幾天,星期天開(kāi)始0-6
  $dn = $w ? $w - $first : 6;//要減去的天數(shù)
  //本周開(kāi)始日期
  $st = date("Y-m-d", strtotime("$gdate -".$dn." days"));
  //本周結(jié)束日期
  $en = date("Y-m-d", strtotime("$st +6 days"));
  //上周開(kāi)始日期
  $last_st = date('Y-m-d',strtotime("$st - 7 days"));
  //上周結(jié)束日期
  $last_en = date('Y-m-d',strtotime("$st - 1 days"));
  return array($st, $en,$last_st,$last_en);//返回開(kāi)始和結(jié)束日期
}
echo implode("|", aweek("", 1)).'<br />';
//echo date("Y-m-d",strtotime("time()"));
echo '本周第一天（星期日為一周開(kāi)始）：'.date('Y-m-d', time()-86400*date('w')).'<hr>';
echo '本周第一天（星期一為一周開(kāi)始）：'.date('Y-m-d', time()-86400*date('w')+(date('w')>0?86400:-6*86400)).'<hr>';
echo '本月第一天：'.date('Y-m-d', mktime(0,0,0,date('m'),1,date('Y'))).'<hr>';
echo '本月最后一天：'.date('Y-m-d', mktime(0,0,0,date('m'),date('t'),date('Y'))).'<hr>';
//上個(gè)月的開(kāi)始日期
$m = date('Y-m-d', mktime(0,0,0,date('m')-1,1,date('Y')));
//上個(gè)月共多少天
$t = date('t',strtotime("$m"));
echo '上月第一天：'.date('Y-m-d', mktime(0,0,0,date('m')-1,1,date('Y'))).'<hr>';
echo '上月最后一天：'.date('Y-m-d', mktime(0,0,0,date('m')-1,$t,date('Y'))).'<hr>';

//PHP手冊(cè)上有一個(gè)這個(gè)方法，用來(lái)返回指定日期的周一和周日
function get_week_range($week, $year){
  $timestamp = mktime(1,0,0,1,1,$year);
  $firstday = date("N",$timestamp);
  if($firstday >4){
    $firstweek = strtotime('+'.(8-$firstday).' days', $timestamp);
  }else{
    $firstweek = strtotime('-'.($firstday-1).' days', $timestamp);
  }
  $monday = strtotime('+'.($week - 1).' week', $firstweek);
  $sunday = strtotime('+6 days', $monday);
  $start = date("Y-m-d", $monday);
  $end = date("Y-m-d", $sunday);
  return array($start, $end);
}
//strtotime獲取本周第一天和最后一天方法的BUG
//PHP手冊(cè)上有一個(gè)這個(gè)方法，用來(lái)返回指定日期的周一和周日
function get_week_range2($week, $year){
  $timestamp = mktime(1,0,0,1,1,$year);
  $firstday = date("N",$timestamp);
  if($firstday >4){
    $firstweek = strtotime('+'.(8-$firstday).' days', $timestamp);
  }else{
    $firstweek = strtotime('-'.($firstday-1).' days', $timestamp);
  }
  $monday = strtotime('+'.($week - 1).' week', $firstweek);
  $sunday = strtotime('+6 days', $monday);
  $start = date("Y-m-d", $monday);
  $end = date("Y-m-d", $sunday);
  return array($start, $end);
}

if(date('m',$last_week_time) == '01' and $tmp_last_week > 10){
  $last_week_year--;
}