We can use either
session_register or $_SESSION for registering session variable in php.
Find below the difference between both of them.
session_register() is a function and
$_SESSION is a superglobal array.
session_register() is used to register a session variable and it works only when
register_globals is turned on. (Turning ON register_globals will create mesh-ups, but some applications (e.g OScommerce) requires turning ON of register_globals)
$_SESSION works even when register_globals is turned off.
If session_start() was not called before
session_register() is called, an implicit call to session_start() with no parameters will be made. But
$_SESSION requires session_start() before use.