$pre_url = $_SERVER['HTTP_REFERER'];
$t = parse_url($pre_url);
$a1 = array();
$a2 = array();

parse_str($t['query'],$a1);
parse_str($_SERVER['QUERY_STRING'],$a2);

$sort = array('a','b','c','d');//初始排序

if (!empty($a2['sort'])){
    $t = explode(',', $a2['sort']);//请求方式
    $t1 = array_diff($sort, $t);
    foreach ($sort as &$v){
        if (in_array($v,$t)){
            $tmp = array_diff($t, array($v));
            if (!empty($tmp))
            $v .= ','.implode(',', array_diff($t, array($v)));
        }else{
            $v .= ','.$a2['sort'];
        }
    }
}
echo sprintf('
<a href="%s">clear</a>
<a href="?sort=%s">a</a>
<a href="?sort=%s">b</a>
<a href="?sort=%s">c</a>
<a href="?sort=%s">d</a>
',$_SERVER['PHP_SELF'],$sort[0],$sort[1],$sort[2],$sort[3]);

------解决方案--------------------
换了个面孔,加了点注释.
PHP code

$query_string = $_SERVER['QUERY_STRING'];//获取此次请求的条件串

$sort = array('a=1','b=2','c=3','d=4');//初始条件
$dep = '&';//分隔符,可以用于rewrite

if (!empty($query_string)){
    $current_options = explode($dep, $query_string);//当前请求条件数组
    echo '<pre>';
    print_r($current_options);//输出条件,查看当前的条件.
    echo '</pre>';
    
    foreach ($sort as &$v){//此处循环是用来改变初始条件数组
        if (in_array($v,$current_options)){//判断当前数组成员是否已经存在
            $tmp = array_diff($current_options, array($v));//差集用来添加
            if (!empty($tmp)){
                $v .= $dep.implode($dep, $tmp);
            }
        }else{//不存在即添加
            $v .= $dep.$query_string;
        }
    }
    
}
echo sprintf('
<a href="%s">clear</a>
<a href="?%s">a</a>
<a href="?%s">b</a>
<a href="?%s">c</a>
<a href="?%s">d</a>
',$_SERVER['PHP_SELF'],$sort[0],$sort[1],$sort[2],$sort[3]);

------解决方案--------------------
探讨


换了个面孔,加了点注释.
PHP code

$query_string = $_SERVER['QUERY_STRING'];//获取此次请求的条件串

$sort = array('a=1','b=2','c=3','d=4');//初始条件
$dep = '&amp;';//分隔符,可以用于rewrite

if (!empty($query_string)){
    $curren……