正如你在注释中所说，如果你想通过AJAX加载链接：/ p>

您的标记：

 < a href =test / function data-key =abc> 
 

您的jquery：

  $（'a'）。on（'click'，function（）{
 var data = $（this）.data（'key'）; 
 $（'结果'）。load（$（this）.attr（href）+'？key ='+ data）; 
}）;然后在你的CodeIgniter控制器，你检查你的密钥是否存在和匹配（abc ） 

另外，你也可以检查 $ _ SERVER ['HTTP_REFERER'] 查看用户来自哪里（这是很容易欺骗），并且只有当GET请求是从您自己的网站发出时才允许访问。
 
I want to know if there is any way through which I can restrict access to my controller functions through URL. But I want to give them a call through my link in the site. For example if I have a link in my site which points to a controller function:
<a href='test/function'>Call me</a>

But I don't want the controller function to be called when I place the above URL in my browser address bar. Can anyone help with this?

As you stated in the comment, that if you want to load the link via AJAX:

Your markup:
<a href="test/function" data-key="abc">

Your jquery:
$('a').on('click',function(){
    var data = $(this).data('key');
    $('#result').load($(this).attr("href") + '?key=' + data);
});

Then in you CodeIgniter controller, you check to see if your key is present and matches ("abc"), else you return a 403 or something simillar.

Also, you could of course check the $_SERVER['HTTP_REFERER'] to see where the user came from (this is however quite easily spoofed) and only allow access when the GET-request is made from your own site.