Php 从MySQL改为MySQLi，不再工作

在将mysql改为mysqli的过程中，我从一个完全可以工作的php文件变成了一个不能工作的文件！每次更换我都按照说明进行，你能帮我吗？以下是我在mysql之前和之后的代码：

之前（mysql）：

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$dtbhost变量应为IP地址或域名。例如：“localhost”、“127.0.0.1”、“example.com”等。。不是套接字文件。
你知道主机是什么吗？很抱歉，但是，查找一下套接字和主机的区别是的，我刚才注意到了，但是因为它在mysql上工作，我认为这没有错！Mysql可以使用套接字和主机？好的，那么mysqli需要一个主机，而Mysql需要一个套接字？是这样吗？mysql驱动程序可以连接到主机或套接字（两者都可以）mysqli驱动程序只能连接到主机或主机：非常感谢！你知道我是否可以从套接字链接中获取主机地址吗？它看起来像是同一台机器，所以应该是简单的“localhost”或“127.0.0.1”
<?php

function db_open() {
    $dtbhost=":/something/home/something2/mysql/run/mysql.sock";
    $dtbuser="root";
    $dtbpass="mypass";
    $dtbname="mydb";
    $connection   =   mysql_connect("$dtbhost",   "$dtbuser",   "$dtbpass") 
        or die('00: No Connection');
    @ mysql_select_db("$dtbname") or die('01: No Database');      
}

session_start(); // Starting Session
$error=''; // Variable To Store Error Message
if (isset($_POST['submit'])) {
    if (empty($_POST['username']) || empty($_POST['password'])) {
        echo ("<SCRIPT LANGUAGE='JavaScript'> 
            window.alert('You did not complete all of the required fields') 
            window.location.href='index.html' 
            </SCRIPT>");
    }
    else
    {
    // Define $username and $password
    $username=$_POST['username'];
    $password=$_POST['password'];
    // Establishing Connection with Server by passing server_name, user_id and password as a parameter
    db_open(); 
    // To protect MySQL injection for Security purpose
    $username = stripslashes($username);
    $password = stripslashes($password);
    $username = mysql_real_escape_string($username);
    $password = mysql_real_escape_string($password);
    $query = mysql_query("SELECT * FROM login_users WHERE username = '$username' AND password = '$password'") 
            or die(mysql_error());

    $rows = mysql_num_rows($query);
    if ($rows == 1) {
        $_SESSION['login_user']=$username; // Initializing Session
        header("location: profile.html"); // Redirecting To Other Page

    } else {
        echo ("<SCRIPT LANGUAGE='JavaScript'> 
            window.alert('Wrong username password combination. Please re-enter.') 
            window.location.href='index.html' 
            </SCRIPT>");
    }
    mysql_close($connection); // Closing Connection
    }
}
?>

<?php

function db_open() {
    $dtbhost=":/something/home/something2/mysql/run/mysql.sock";
    $dtbuser="root";
    $dtbpass="mypass";
    $dtbname="mydb";
    $con = mysqli_connect("$dtbhost","$dtbuser","$dtbpass","$dtbname");

    // Check connection
    if (mysqli_connect_errno())
      {
        echo "Failed to connect to MySQL: " . mysqli_connect_error();
      }
}

session_start(); // Starting Session
$error=''; // Variable To Store Error Message
if (isset($_POST['submit'])) {
    if (empty($_POST['username']) || empty($_POST['password'])) {
        echo ("<SCRIPT LANGUAGE='JavaScript'> 
            window.alert('You did not complete all of the required fields') 
            window.location.href='index.html' 
            </SCRIPT>");
    }
    else
    {
    // Define $username and $password
    $username=$_POST['username'];
    $password=$_POST['password'];
    // Establishing Connection with Server by passing server_name, user_id and password as a parameter
    db_open(); 
    // To protect MySQL injection for Security purpose
    $username = stripslashes($username);
    $password = stripslashes($password);
    $username = mysqli_real_escape_string($con, $username);
    $password = mysqli_real_escape_string($con, $password);

    $query = mysqli_query($con, "SELECT * FROM login_users WHERE username = '$username' AND password = '$password'") 
            or die(mysqli_error());

    $rows = mysqli_num_rows($query);
    if ($rows == 1) {
        $_SESSION['login_user']=$username; // Initializing Session
        header("location: profile.html"); // Redirecting To Other Page

    } else {
        echo ("<SCRIPT LANGUAGE='JavaScript'> 
            window.alert('Wrong username password combination. Please re-enter.') 
            window.location.href='index.html' 
            </SCRIPT>");
    }
    mysqli_close($con); // Closing Connection
    }
}
?>