获取指定字符串中间的值

//                  字符串  起始字符串 结束字符串
function GetBetween($content,$start,$end){
        $r = explode($start, $content);
        if (isset($r[1])){
            $r = explode($end, $r[1]);
            return trim($r[0]);
        }
        return '';
      }