<?php
//global $bdd;
header('Content-type: text/html; charset=UTF-8');
//// connexion
function connect_mysql() {
include_once (dirname(__DIR__).'\pdo\new\MyPdo.php');

try{
				$bdd = new MyPdo();
				$_SESSION["bdd"]=serialize($bdd);
				return($bdd);
			}
catch(PDOException $e){
				echo "argggggggggggggg".$e->getMessage();
				return(FALSE);
			}
}
		
?>

You cannot serialize or unserialize PDO instances

<?PHP
function local ()
{
	print "<br>dump entrée de local  : ";
	var_dump($a);
	$a = 2;
	print "<br>dans fonction local $a";
}
function globale ()
{
	global $a;
	print "<br>dump entrée de globale : ";
	var_dump($a);
	$a = 2;
	print "<br>dans fonction globale $a";
}
function utile()
{
	return 31;
}
function parametre($a)
{
	return $a*10;
}
function paradresse (&$a, $b)
{
	$a = $a*$b;
	
}
function globalisant ($a,$b)
{
	global $texte;
	$div = $a /$b;
	print "<br>$texte : $div";
}
$a = 4;
print "principal avant $a";
local();
print "<br>après local $a";
globale ();
print "<br>après globale $a";
$a = utile();
print "<br>après utile $a";
$b = parametre($a);
print "<br>b après parametre $b";
print "<br>a après parametre $a";
paradresse($a, $b);
print "<br>b après paradrese $b";
print "<br>a après paradresse $a";
include ("barratin");
globalisant ($a, $b);
?>

<?php
session_start();
error_reporting(E_ALL ^ (E_NOTICE|E_WARNING|E_DEPRECATED));
//global $bdd;

include dirname(__DIR__)."\pdo\connect_mysql.php";
if ((empty($bdd))) {
	$bdd=connect_mysql();
	}
...

<?php
session_start();
//global $bdd;
header('Content-type: text/html; charset=UTF-8');
//// connexion
function connect_mysql() {
include_once (dirname(__DIR__).'\pdo\new\MyPdo.php');

try{
				$bdd = new MyPdo();
				$_SESSION['bdd']=$bdd;
				return($bdd);
			}
catch(PDOException $e){
				echo "argggggggggggggg".$e->getMessage();
				return(FALSE);
			}
}
		
?>

<?php
error_reporting(E_ALL ^ E_DEPRECATED ^ E_NOTICE);
ini_set('display_errors','1'); 
// MyPDO
 // ls : la classe MyPdo hérite de la classe PDO (extends)
class MyPdo extends PDO {

	static public $DB_NAME = "su_dev_eis"; // ls : static public, je sais + pourquoi...

	static public $HOST = "localhost";
	
	static public $USER ="root";

	static public $PASS ="root";
	
// ls : le constructeur de MyPdo appelle le constructeur de PDO en lui passant ses paramètres	
	function __construct() {
	/* ls : la variable $pdo_options, ça date de ma formation de 2012 */ 
	$pdo_options[PDO::ATTR_ERRMODE] = PDO::ERRMODE_EXCEPTION;
	$pdo_options[PDO::ATTR_EMULATE_PREPARES] = false;//important sur les configs récentes
	$pdo_options[PDO::ATTR_DEFAULT_FETCH_MODE] = PDO::FETCH_OBJ;//pour le mode objet
	$pdo_options[PDO::MYSQL_ATTR_INIT_COMMAND] = "SET NAMES utf8";//pour l'utf-8
 
	parent::__construct('mysql:host=' . MyPdo::$HOST . ';dbname=' . MyPdo::$DB_NAME, MyPdo::$USER,MyPdo::$PASS, $pdo_options);
//MyPdo::$USER
	}

}
// fin MyPDO
?>

<?php
session_start();
...
include dirname(__DIR__)."\header.inc.php";
...

<?php
session_start();
...
$bdd=$_SESSION['bdd'];
...
var_dump($bdd);
$query1="SELECT * from users WHERE user='".$_SESSION['user']."'";
$qid = $bdd->prepare($query1);
$qid->execute();
...

<?PHP
	include ("connect.php");
	$bdd= NULL;//peut être supprimé
	connect();
	var_dump ($bdd);
print "<a href = 'chose.php'>aaaa</a>";
?>
<?PHP
function connect()
{
global $bdd;
	$bidule = $mysqli = mysqli_init();
	if (!$bidule)
	{ 
		return False;
	}
	else
	{
		$bdd = mysqli_real_connect($bidule, 'localhost', 'root', '', 'lexique');
		if (!$bdd)
		{		
			return FALSE;
		}
		else
		{
			print "ok";
		}
	}
}
?>

<?PHP
	include ("connect.php");
	$bdd = connect();
	var_dump ($bdd);
print "<a href = 'chose.php'>aaaa</a>";
?>

<?PHP
function connect()
{
	$bidule = $mysqli = mysqli_init();
	if (!$bidule)
	{ 
		return False;
	}
	else
	{
		$truc = mysqli_real_connect($bidule, 'localhost', 'root', '', 'lexique');
		if (!$truc)
		{		
			return FALSE;
		}
		else
		{
			return $truc;
		}
	}
}
?>

<?php
error_reporting(E_ALL ^ (E_NOTICE|E_WARNING|E_DEPRECATED));
global $bdd;

include dirname(__DIR__)."\pdo\connect_mysql.php";
if ((!isset($bdd)))
	$bdd=connect_mysql();
...
?>