Variable undefined despite successfully using require(); in PHP-CodePudding

I have a connect.php file which is supposed to verify the successful connection to my database. I then have a db.php file in which I've imported the connect.php file using the require('connect.php'); function in PHP. My IDE however still gives me an error saying that the $conn variable (as defined in the code below) is not defined. At first I thought that the import of connect.php into the db.php file may have somehow failed but this seems to not be the case since launching db.php file in the browser returns "Database connection success" which should not be possible unless the connect.php file has been correctly imported.

This is the content of the connect.php file :

<?php

$host = 'localhost';
$usr = 'root';
$passwd = '';
$db_name = 'testdb';

$conn = new MySQLi($host, $usr, $passwd, $db_name);

if($conn->connect_error){
    die('Database connection failure: ' . $conn->connect_error);
} else{
    echo "Database connection success.";
}

I then try to import this code into the db.php as seen below :

<?php

require('connect.php');

$sql = "SELECT * FROM users";
$stmt = $conn->prepare($sql);

However in db.php the $conn variable is undefined for some reason. Why is it undefined despite the import of it's definition being successful?

CodePudding user response：

This happens to me in PHPStorm if I incorrectly define the project root (even if this shouldn't be your case) or the include path.

Basically, the IDE can't "see" inside the connect.php and therefore acts as if the variables defined there don't exist.

You could try defining a class to handle connections. This is a dirty hack:

<?php
    class MyConnection
    {
        private static $conn = null;

        public static instance() {
            if (null === static::$conn) {
                $host = 'localhost';
                $usr = 'root';
                $passwd = '';
                $db_name = 'testdb';
                static::$conn = new MySQLi($host, $usr, $passwd, $db_name);
                if(static::$conn->connect_error) {
                    die('Database connection failure: ' . static::$conn->connect_error);
                }
            }
            return static::$conn;
        }
    }

and then in the db.php,

require('connect.php');

$sql = "SELECT * FROM users";
$stmt = MyConnection::instance()->prepare($sql);

The difference being that I noticed some IDEs (PHPStorm and Microsoft VSCode) sometimes seem to handle classes way better than global symbols.

One of the advantages of this approach is that, in larger projects, if you define an autoloader, you can avoid most require and include altogether, and only load files on demand.

In this case, it's just an ugly hack that perhaps keeps the IDE happy. If you can fix things by e.g. informing the IDE about your project files and/or include paths, by all means you should do that.

I would avoid the tricks of declaring

global $conn;

because you might not notice when you use a variable that's globally undefined, or worse silencing the warnings with special comments because that makes you miss all undefined symbols.

/** @noinspection PHPUndefinedSymbol */

If nothing else avails, surrender and define a dummy variable:

/* dummy connection */
$conn = null;

require 'connect.php';

...

CodePudding user response：

The error seems to be some sort of an error related to my IDE. If you encounter similar issues you may ignore this error or change the IDE highlighting properties to reflect such code style. If you are trying to use the variable inside of a function try to make the variable global using global $conn; (in my case). Putting the variable inside of the function and changing it's scope to global seems to have removed the error from the IDE completely.