PHP Convert mysql to mysqli [duplicate]

问题:

This question already has answers here:

Can I mix MySQL APIs in PHP? (4 answers)

Closed last month.

The following script works fine:

$host="localhost"; // Host name 
$username=""; // Mysql username 
$password=""; // Mysql password 
$db_name="test"; // Database name 
$tbl_name="members"; // Table name 

// Connect to server and select databse.
mysql_connect("$host", "$username", "$password")or die("cannot connect"); 
mysql_select_db("$db_name")or die("cannot select DB");

// username and password sent from form 
$myusername=$_POST['myusername']; 
$mypassword=$_POST['mypassword']; 

// To protect MySQL injection (more detail about MySQL injection)
$myusername = stripslashes($myusername);
$mypassword = stripslashes($mypassword);
$myusername = mysql_real_escape_string($myusername);
$mypassword = mysql_real_escape_string($mypassword);
$sql="SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword'";
$result=mysql_query($sql);

// Mysql_num_row is counting table row
$count=mysql_num_rows($result);

// If result matched $myusername and $mypassword, table row must be 1 row
if($count==1){

// Register $myusername, $mypassword and redirect to file "login_success.php"
session_register("myusername");
session_register("mypassword"); 
header("location:login_success.php");
}
else {
echo "Wrong Username or Password";
}

Why, when I replace only the mysql_connect and mysql_select_db statements (keeping everything else including all passwords the same) with the following, do i get the "Wrong Username or Password" echo?

mysqli_connect($host,$username,$password,$db_name) or die("cannot connect");

回答1:

It is because the MySQL and MySQLi database connections are not linked. When you make a connection to database with MySQLi, you have to use that connectio.

Example:

$mysqli = new mysqli('localhost', 'user', 'password', 'database');
$result = $mysqli->query("SELECT * FROM users");