Does the PHP check form submission come from this site

Method One:
You can write code that deals with submitting data into a separate file, such as form.php.    
  <?php   
  if    defined (' INSIDE ')    {//to determine whether there is a defined INSIDE constant    
  //processing form    
  }   else   {   
  exit (' ERROR ');    
  }   
  ?>   
     
   Then, on the page that submits the form, define the INSIDE constant, and the constant value doesn't matter    
  define (' INSIDE ',     ' TRUE ');   
    
   Then, to determine whether there is a commit, if submitted, then    
  include    ' form.php ';

======================================================================================= Method two:

<?php 
if (php_version< ' 4.1.0 ') {$_server =  $HTTP _server_vars;}  
if (IsseT ($_server["http_referer"])) { 
//For some browsers may not have http_referer, so make a judgment  
    $ servername=$_server[' server_name ']; 
     $sub _from=$_server["Http_referer"]; 
     $sub _len=strlen ($servername); 
     $checkfrom =substr ($ sub_from,7, $sub _len); 
    if ($checkfrom!= $servername)  
     { 
        echo  "<script language=" JavaScript ' >window.alert (' The data source is wrong, this station does not receive the data from the receiving terminal! '); Window.opener=self;window.close ();</script> "; 
         exit; 
    } 
} 
?> 
     This method is not absolutely safe, Because Http_referer can be forged, can only be a gentleman but can not prevent the villain, but under normal circumstances already enough.