Simple PHP MySQL $con undefined - php

Question

Solution:
I tinkered around with kcdwayne's test (using test.php and register.php) and determined that the issue resided in using the file name "db.php." I renamed it to "datab.php" and it appears to be working wherever it is being used. Interesting. Thank you for your answers!
Original Post:
I have one file - checkuser.php - that is POST'd to from a login form to verify a user's credentials. username and password are given. Through an external file - db.php - I am trying to establish a connection to the MySQL database. The setup:
checkuser.php:
session_start();
error_reporting(E_ALL);
ini_set( 'display_errors','1');
require "db.php";
db.php:
$con = mysqli_connect("server", "user", "pass", "db");
if (mysqli_connect_errno($con)) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
... later in checkuser.php:
$username = $_POST['username'];
$password = $_POST['password'];
$sql = mysqli_query($con, "SELECT * FROM userdata WHERE username='$username' AND password='$password' AND activation='true'");
And thus, here lies my problem:
Notice: Undefined variable: con in /path/to/checkuser.php on line 23
checkuser.php and db.php are in the same folder; the MySQL connection can easily be established if the code in db.php is moved into checkuser.php itself.
What am I doing wrong?
checkuser.php:
<?php
session_start();
error_reporting(E_ALL);
ini_set( 'display_errors','1');
require "db.php";
$username = $_POST['username'];
$password = $_POST['password'];
if((!$username) || (!$password)){
echo "<font color='white'>Please enter ALL of the information! <br />";
include 'login.php';
exit();
}
$password = md5($password);
$sql = mysqli_query($con, "SELECT * FROM userdata WHERE username='$username' AND password='$password' AND activation='true'");
$login_check = mysqli_num_rows($sql);
if($login_check > 0) {
while($row = mysqli_fetch_assoc($sql)) {
... set some $_SESSION variables ...
}
}
?>
db.php:
<?php
$con = mysqli_connect("server", "user", "password", "database");
if (mysqli_connect_errno($con)) {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
?>

Answer 1

If db.php is included/required on checkuser.php, the variable should be there, provided that:
$con is not scoped inside of a block where checkuser.php does not have access to.
The place you're requesting it can receive it (i.e., it's passed as an argument into the function or it's not wrapped in a scope that does not have access to $con.
Try this:
make a file called test.php, and in it, place
$var = 'this is my test var';
then make a file in the same folder called register.php, and put only
require('test.php');
echo $var;
If it works, your problem's either in scope or it just isn't loading the db.php.