php pdo connection

1<?php
2$servername = "localhost";
3$username = "username";
4$password = "password";
5
6try {
7    $conn = new PDO("mysql:host=$servername;dbname=myDB", $username, $password);
8    // set the PDO error mode to exception
9    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
10    echo "Connected successfully";
11    }
12catch(PDOException $e)
13    {
14    echo "Connection failed: " . $e->getMessage();
15    }
16?>

1$host     = "localhost";//Ip of database, in this case my host machine    
2$user     = "root";	//Username to use
3$pass     = "qwerty";//Password for that user
4$dbname   = "DB";//Name of the database
5
6try {
7    $connection = new PDO("mysql:host=$host;dbname=$dbname", $user, $pass);
8    $connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
9
10}catch(PDOException $e)
11{
12  echo $e->getMessage();                         
13}

1<?php
2class database{
3  private $host = "localhost";
4  private $db_name = "php_basic";
5  private $username = "root";
6  private $password = "";
7  private $conn;
8
9  // connect database using PDO
10  function connect_pdo(){
11    try{
12      $this->conn = new PDO("mysql:host=".$this->host.";dbname=".$this->db_name, $this->username, $this->password);
13      return $this->conn;
14    }
15    catch(PDOException $ex){
16      echo "Connection Error -->> ",$ex->getMessage();
17      echo "<br>Error Code -->> ",$ex->getCode();
18      echo "<br>Error occur in File -->> ",$ex->getFile();
19      echo "<br>Error occur on Line no -->> ",$ex->getLine();
20
21      $this->conn = null; // close connection in PDO
22    }
23  }
24}
25?>
26  
27//how to use 
28<?php
29include 'connect_db.php';
30$database=new database();
31$db = $database->connect_pdo();
32?>

1<?php
2$servername = "localhost";
3$username = "username";
4$password = "password";
5
6try {
7  $conn = new PDO("mysql:host=$servername;dbname=myDB", $username, $password);
8  // set the PDO error mode to exception
9  $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
10  echo "Connected successfully";
11} catch(PDOException $e) {
12  echo "Connection failed: " . $e->getMessage();
13}
14?>

1<?php
2$pdo = new PDO('mysql:host=localhost;dbname=databasename', 'username', 'password');
3?>
4

1<?php
2$db = new PDO('mysql:host=myhost;dbname=mydb', 'login', 'password');
3
4
5