Check If PHP Session Has Already Started

Check if PHP session has already started

Recommended way for versions of PHP >= 5.4.0 , PHP 7, PHP 8

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

Reference: http://www.php.net/manual/en/function.session-status.php

For versions of PHP < 5.4.0

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

Load session_start() only if session does not exist?

isset is generally the proper way to check if predefined variables are currently defined:

If you are using a version of php prior to 5.4,

you can usually get away with and its tempting just doing the code below, but be aware that if for some reason sessions are disabled, session_start() will still be called which could end up leading to errors and needless debugging since the $_SESSION array isn't allowed to be created.

if(!isset($_SESSION)){session_start();}

if you want to account for checking to see if sessions are disabled for some reason, you can supress the error message, set a test session variable, and then verify it was set. If its not, you can code in a reaction for disabled sessions. You'll want to do all this at or near the start of your script. So as an example(works differently depending on error handling setting):

if(!isset($_SESSION)){session_start();}
$_SESSION['valid'] = 'valid';
if($_SESSION['valid'] != 'valid')
{
   //handle disabled sessions
}

However, if you are using php version 5.4 or greater,

You can use the session_status() function, a better option as it accounts for sessions being disabled and checks if a session already exists.

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

NOTE that PHP_SESSION_NONE is a constant set by PHP and therefore does not need to be wrapped in quotes. It evaluates to integer 1, but as its a constant that was specifically set to eliminate the need for magic numbers, best to test against the constant.

PHP sessions that have already been started

Try

<?php
    if(!isset($_SESSION)) 
    { 
        session_start(); 
    } 
?>

PHP session has already been started

You should check the session status with session_status() function to avoid repeated session start. For example:

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

Check if session exists in php

Use isset function

function ifsessionExists(){
// check if session exists?
  if(isset($_SESSION)){
    return true;
  }else{
    return false;
  }
 }

You can also use empty function

 function ifsessionExists(){
// check if session exists?
  if(!empty($_SESSION)){
    return true;
  }else{
    return false;
  }
 }

How can you check if a PHP session exists?

In PHP versions prior to 5.4, you can just the session_id() function:

$has_session = session_id() !== '';

In PHP version 5.4+, you can use session_status():

$has_session = session_status() == PHP_SESSION_ACTIVE;

Detect if PHP session exists

If $_SESSION (or $HTTP_SESSION_VARS for PHP 4.0.6 or less) is used, use isset() to check a variable is registered in $_SESSION.

isset($_SESSION['varname'])

How do check if a PHP session is empty?

I would use isset and empty:

session_start();
if(isset($_SESSION['blah']) && !empty($_SESSION['blah'])) {
   echo 'Set and not empty, and no undefined index error!';
}

array_key_exists is a nice alternative to using isset to check for keys:

session_start();
if(array_key_exists('blah',$_SESSION) && !empty($_SESSION['blah'])) {
    echo 'Set and not empty, and no undefined index error!';
}

Make sure you're calling session_start before reading from or writing to the session array.

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