PHP - session_id() Function

Sessions or session handling is a way to make the data available across various pages of a web application. The session_id() function is used to set or retrieve a custom id to the current.
session_id([$id]);

name(Optional)
This is a string value representing the id of the session, if you want to set id of the session using this method.
This returns a String representing the id of the current session (if it has any) or, an empty string if current session doesn’t have any id.
This function was first introduced in PHP Version 4 and works in all the later versions.
Following example demonstrates the usage of the session_id() function.
<html>   
   <head>
      <title>Setting up a PHP session</title>
   </head>   
   <body>
      <?php  
         //Starting the session
         session_start();   
         $id = session_id();
         print("Session Id: ".$id);
      ?>
   </body>   
</html>
One executing the above html file it will display the following message −
Session Id: b9t3gprjtl35ms4sm937hj7s30

Following is another example of this function, in here we have two pages from the same application in the same session.
session_page1.htm
<?php
   if(isset($_POST['SubmitButton'])){ 
      //Starting the session	
      $id = session_create_id();	
      session_id($id);
      print("\n"."Id: ".$id);
      session_start();  
      $_SESSION['name'] = $_POST['name'];
      $_SESSION['age']  = $_POST['age'];	  
      session_commit();
   }
?>
<html>
   <body>
      <form action="#" method="post">
         <label for="fname">Enter the values click Submit and click on Next</label>
         <br><br><label for="fname">Name:</label>
         <input type="text" id="name" name="name"><br><br>
         <label for="lname">Age:</label>
         <input type="text" id="age" name="age"><br><br>           
         <input type="submit" name="SubmitButton"/>
         <?php 
            echo '<br><br /><a href="session_page2.htm">Next</a>';
         ?>
      </form>
   </body>
</html>
This will produce the following output −
Once you press submit the page will be like −
On clicking on Next the following file is executed.
session_page2.htm
<html>   
   <head>
      <title>Second Page</title>
   </head>
   <body>
      <?php
         //Session started
         session_start();
         print("Values from the session with id: ".session_id());
         echo "<br>";
         print($_SESSION['name']); 
         echo "<br>";
         print($_SESSION['age']);
      ?>   
   </body>   
</html>

This will produce the following output −
Values from the session with id: brb9t3gprjtl35ms4sm937hj7s30
Krishna
30

You can create a custom session id by using this function as shown below −
<html>   
   <head>
      <title>Setting up a PHP session</title>
   </head>   
   <body>
      <?php  
         //Creating a custom session id
         session_id("my-id");
         //Starting the session
         session_start();   
         print("Id: ".session_id());
      ?>
   </body>   
</html> 
One executing the above html file it will display the following message −
Id: my-id


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