How do I resolve this php error

I am using usercake for user management module in my project. This is my first PHP project and I am still learning. I setup the database and usercake project but I keep getting this error -

Notice: Trying to get property of non-object in C:\wamp\www\userCake\models\funcs.user.php on line 170

Notice: Trying to get property of non-object in C:\wamp\www\userCake\models\funcs.user.php on line 172

And this error is caught only when there is no user logged in to the system. Once, a user logs in I no longer get this error. The code responsible is -

function isUserLoggedIn()
{
    global $loggedInUser,$db,$db_table_prefix;
    
    $sql = "SELECT User_ID,
            Password
            FROM ".$db_table_prefix."Users
            WHERE
            User_ID = '".$db->sql_escape($loggedInUser->user_id)."' //line 170
            AND 
            Password = '".$db->sql_escape($loggedInUser->hash_pw)."'  // line 172
            AND
            Active = 1
            LIMIT 1";
    
    $sql = mysql_num_rows($sql);
    
    if($loggedInUser == NULL)
    {
        return false;
    }
    else
    {
        //Query the database to ensure they haven't been removed or possibly banned?
        if(returns_result($sql) > 0)
        {
                return true;
        }
        else
        {
            //No result returned kill the user session, user banned or deleted
            $loggedInUser->userLogOut();
        
            return false;
        }
    }
}

I tried to fix this with my limited knowledge of php but wasn't able to. I guess this error is similar to Object reference not set to an instance of an object in .net. Am I right? If 开发者_开发知识库not, what is causing this error?

How can I fix this?

I guess the first time a User is not logged in, the reference is null, so in line 170, $db->sql_escape($loggedInUser->user_id). is causing something like a null reference. Try moving the

if($loggedInUser == NULL) { return false; }

in the beginning of the code to stop dereferencing if the user is null.

function isUserLoggedIn() {
    global $loggedInUser, $db, $db_table_prefix;

    if ($loggedInUser == NULL) { return false; }
    else {
        $sql = "SELECT User_ID,
                Password
                FROM " . $db_table_prefix . "Users
                WHERE
                User_ID = '" . $db->sql_escape($loggedInUser->user_id) . "'
                AND 
                Password = '" . $db->sql_escape($loggedInUser->hash_pw) . "' 
                AND
                Active = 1
                LIMIT 1";

        //Query the database to ensure they haven't been removed or possibly banned?
        if (returns_result($sql) > 0) { return true; }
        else {
            //No result returned kill the user session, user banned or deleted
            $loggedInUser->userLogOut();

            return false;
        }
    }
}

Replace the function with this. The sql statement shouldnt be set until after it checks if $loggedInUser is null ..

I had the exact same problem,

It seems i had my own database connection whice was initiated after the userCake connection was made, this obviously overides userCake connection making it impossible for it sql_escape.

try to disable any database connection after the userCake inclusion.

BTW you should also remove any session_start() before userCake inclusion. this will cause __php_incomplete_class error in the session

I suspect the global variable $loggedInUser is null as long as the user is not logged in. So using it through SQL to detect if the user is logged in... It's a snake biting its own tail.

You probably want to return false earlier if $loggedInUser is null.