Trouble connecting to Database (php) - php

Question

I am working on a user database and have it set up so that the dropdown menus in my registration form take their values from tables in the database. The problem is that when I tested it out, the dropdowns were empty. Naturally the first thing I did was to go and check my connection. To connect to the database, I have a file called BaseDAO.php which contains the following:
<?php
class BaseDAO {
const SQL_HOST = "localhost";
const SQL_USER = "user6538";
const SQL_PW = "sdWf234Fg";
const SQL_DB = "userDB";
protected $con = null;
function connect() {
$this->con = mysql_connect(self::SQL_HOST, self::SQL_USER, self::SQL_PW);
if(!$this->con) {die('Could not connect to MySQL host: ' . self::SQL_HOST . ' Error: ' . mysql_error()); }
echo "Connected!"; //NOTE: I only just added this to test it
mysql_select_db(self::SQL_DB);
}
function close() {
mysql_close($this->con);
}
}
?>
So to test it, I added echo "Hello World!"; outside of the class, just as a reference, then I added connect(); right below it. I opened my page and only saw the Hello World! ... So then I tried echo connect(); and again nothing. Then I tried this:
$baseDAO = new BaseDAO();
$baseDAO->connect();
And still there was nothing. Then I commented out the entire class and just added this:
<?php
//...
//Commented out class
//....
function connect() {
$con = mysql_connect("localhost", "user6538", "sdWf234Fg" );
if(!$con) { echo "3"; die('Could not connect: ' . mysql_error()); }
echo "Connected!";
}
echo "Hello World!";
connect();
?>
Lo and behold the output was this:
Hello World!Connected!
I don't understand why my class doesn't work... It explains why my dropdowns were not working, since their DAO files require my BaseDAO.
Would someone care to enlighten me on what's going on here? Why won't my class work?
NOTE: I am using a friend's old project as a guide, so theoretically my BaseDAO.php should work, since his worked.
EDIT: Corrected the arguments in the second connect() function

Answer 1

The return value of mysql_connect is FALSE in an error case. 0 is a positive value.
To be sure, make this change:
if(self::con === FALSE) {die('Could not connect to MySQL host: ' . self::SQL_HOST . ' Error: ' . mysql_error()); }
Your second SQL, where you did remove the CLASS parts, cannot work, but it strangely does.
$con = mysql_connect(self::SQL_HOST, self::SQL_USER, self::SQL_PW);
You do not have the self:: constants defined if you class does not exist. PHP should have produced an error message in this case. So your description is wrong and missing something.

Answer 2

class BaseDAO {
private static $SQL_HOST = "localhost";
private static $SQL_USER = "user6538";
private static $SQL_PW = "sdWf234Fg";
private static $SQL_DB = "userDB";
protected static $con = null;
public static function connect() {
self::con = mysql_connect(self::SQL_HOST, self::SQL_USER, self::SQL_PW);
if(!self::con) {die('Could not connect to MySQL host: ' . self::SQL_HOST . ' Error: ' . mysql_error()); }
echo "Connected!"; //NOTE: I only just added this to test it
mysql_select_db(self::SQL_DB);
}
public static function close() {
mysql_close(self::con);
}
}
To connect do the following no need to create an instance of the class because its static:
BaseDAO::connect();