php开启mysqli扩展之后如何连接数据库

<?php 
$connect = mysqli_connect('localhost','root','','volunteer') or die('Unale to connect'); 
$sql = "select * from vol_msg"; 
$result = mysqli_query($connect,$sql); 
while($row = mysqli_fetch_row($result)){ 
echo $row[0]; 
} 
?> 

<?php 
//创建对象并打开连接，最后一个参数是选择的数据库名称 
$mysqli = new mysqli('localhost','root','','volunteer'); 
//检查连接是否成功 
if (mysqli_connect_errno()){ 
//注意mysqli_connect_error()新特性 
die('Unable to connect!'). mysqli_connect_error(); 
} 
$sql = "select * from vol_msg"; 
//执行sql语句，完全面向对象的 
$result = $mysqli->query($sql); 
while($row = $result->fetch_array()){ 
echo $row[0]; 
} 
?>