Predefined Constants
The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.
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SID(string) - Constant containing either the session name and session ID in the form of "name=ID" or empty string if session ID was set in an appropriate session cookie. This is the same id as the one returned by session_id().
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PHP_SESSION_DISABLED(int) - Since PHP 5.4.0. Return value of session_status() if sessions are disabled.
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PHP_SESSION_NONE(int) - Since PHP 5.4.0. Return value of session_status() if sessions are enabled, but no session exists.
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PHP_SESSION_ACTIVE(int) - Since PHP 5.4.0. Return value of session_status() if sessions are enabled, and a session exists.
Коментарии
SID constant defined dynamically!
var_dump(defined('SID')); // bool(false) - Not defined...
session_start();
var_dump(defined('SID')); // bool(true) - Defined now!
Check whether session started using Predefined Constants
if (session_status() == PHP_SESSION_NONE) {
session_start();
}