php to establish connection to the database

It happens that the variabels are not within the declaration of your class, although you have them in an external file;

  

I have removed the PDO sample.

I update to place an example with mysqli with a separate file, for this we will create a config file called config.php.ini to have the credentials in an external file;

config.php.ini

<?php return; ?>
; credenciales
host=localhost
usuario=elusuariodeladb
clave="laclave"
dbnombre=elnombredeladb

Now our class connection, in the same note that you do not have to call the function require or include since the function parse_ini_file is responsible for reading the file and assigning its value to the property credentials; conexion.php

class conexion {
    //Esta vez solo necesitaremos una propiedad que es de tipo array
    private $credenciales;
    protected $myconn;

    function connect() {
       $this->credenciales = parse_ini_file("config.php.ini");
        $con = mysqli_connect($this->credenciales["host"], $this->credenciales["usuario"], $this->credenciales["clave"], $this->credenciales["dbnombre"]);
        if (!$con) {
            die('no se ha podido conectar con la base de datos!');
        } else {
            $this->myconn = $con;
            echo 'exitosa';}
        return $this->myconn;
    }

    function close() {
        mysqli_close($myconn);
        echo 'conexion cerrada';
    }

}

Here is an example with mysqli

  

Consider that if you are creating a script that will serve to make   a connection to a server for example of databases; so he   appropriate access modifier in this case should be private then   they will only be available within the class that owns them

<?php

class Conexion 
{
    private $host;
    private $user;
    private $pass;
    private $dbname;

    public function __construct($host, $user, $pass, $dbname)
    {
        $this->host = $host;
        $this->user = $user;
        $this->pass = $pass;
        $this->dbname = $dbname;
    }

    public function createConecction()
    {
        $conecta = new mysqli($this->host, $this->user, $this->pass, $this->dbname);
        return ($conecta) ? 'conectado' : 'no conectado';
    }
}

$obj = new Conexion("localhost", "root", "password", "demo");
echo $obj->createConecction(); //imprimirá conectado

  

The first thing I do is declare the properties, later   I declare a magical method construct() to initialize the   properties when the class is created; finally I create a method   personalized that is the one that contains the call to the   mysqli

     

I also make the observation, the properties that you will use the   you must declare within the scope of the class to recognize them   as such when you want to use them; so I do not see it necessary that the   declare in another file and then invoke it