您路由括号有问题，只需将其从{}更改为（）括号即可
自

$route['subjects/(:num)/{:any}'] = 'subjects/view/$1/$2';

至

$route['subjects/(:num)/(:any)'] = 'subjects/view/$1/$2';

始终维护路由规则
喜欢

$route['subjects/(:num)/(:any)/(:any)/(:any)'] = 'subjects/view/$1/$2/$3/$4';
$route['subjects/(:num)/(:any)/(:any)'] = 'subjects/view/$1/$2/$3';
$route['subjects/(:num)/(:any)'] = 'subjects/view/$1/$2';

始终遵循此路由模式
如果你这样加

$route['subjects/(:num)/(:any)'] = 'subjects/view/$1/$2';
$route['subjects/(:num)/(:any)/(:any)/(:any)'] = 'subjects/view/$1/$2/$3/$4';
$route['subjects/(:num)/(:any)/(:any)'] = 'subjects/view/$1/$2/$3';

则第一条件每次总是为真。
另请参考此链接--〉codeigniter routing rules

我曾经尝试过这种URI模式

$route['(:any)'] = 'welcome/list1/$1';
$route['(:any)/(:num)'] = 'welcome/list1/$1/$2';

$route['(:any)/(:any)'] = 'welcome/list2/$1/$2';
$route['(:any)/(:any)/(:num)'] = 'welcome/list2/$1/$2/$3';

$route['(:any)/(:any)/(:any)'] = 'welcome/list3/$1/$2/$3';

但是它不起作用...所以我用正则表达式替换了它
([a-z 0-9 -]+)替换了(:any)，([0-9]+)替换了(:num)
所以它变成了

$route['([a-z 0-9 -]+)'] = 'welcome/list1/$1';
$route['([a-z 0-9 -]+)/([0-9]+)'] = 'welcome/list1/$1/$2';

$route['([a-z 0-9 -]+)/([a-z 0-9 -]+)'] = 'welcome/list2/$1/$2';
$route['([a-z 0-9 -]+)/([a-z 0-9 -]+)/([0-9]+)'] = 'welcome/list2/$1/$2/$3';

$route['([a-z 0-9 -]+)/([a-z 0-9 -]+)/([a-z 0-9 -]+)'] = 'welcome/list3/$1/$2/$3';

而且对我很有效：）
为了访问控制器中的变量，您可以在函数中指定任何参数。

class Welcome extends CI_Controller {

    public function list($first, $second)
    {
        var_dump($first);
        var_dump($second);
    }
}