How does session_id() differ from the constant SID in PHP?

session_id() allows you to set or get the current session id, while the constant SID contains the session name followed by an equal sign and the session ID. Using session_id() gives you more control over the session id, while SID is automatically generated by PHP. If you want to manually set or get the session id, use session_id(). If you just need to include the session id in URLs, use SID. 

<?php
// Using session_id()
session_start();
$custom_session_id = "my_custom_id";
session_id($custom_session_id);

// Using SID
session_start();
echo '<a href="page.php?' . SID . '">Link</a>';
?>

Keywords

session_id constant SID PHP difference

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