How Can I Safely Check if a PHP Session Has Already Started Before Calling `session_start()`?

Checking if a PHP Session Has Already Started

When working with PHP sessions, it's important to ensure that the session has not already been started before calling the session_start() function. Failure to do so can result in an error message being displayed. This article discusses two common methods for checking whether a session has been started to mitigate this issue.

Recommended Method (PHP >= 5.4.0, PHP 7, PHP 8)

if (session_status() === PHP_SESSION_NONE) {
    session_start();
}

This method utilizes the session_status() function introduced in PHP 5.4.0. It checks the current session status and returns one of the following constants:

• PHP_SESSION_NONE indicates that no session has been started yet.
• PHP_SESSION_ACTIVE indicates that a session is currently active.

If session_status() returns PHP_SESSION_NONE, it means that no session has been started, and session_start() can be called safely.

Method for PHP

if(session_id() == '') {
    session_start();
}

This method checks the value of the session ID in the cookie to determine whether a session has been started. If the session ID is empty (''), it means that no session has been started, and session_start() can be called.

Using @session_start()

It is not recommended to use the @ operator with session_start(). While it will suppress any warnings caused by calling session_start() twice, it will not resolve the underlying issue. It is best practice to use the recommended method outlined above to check for session status and start a session only if necessary.

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