mysql_real_escape_string() completely removes string

Question

I'm escaping all the string parameters I receive from a php form like this:

$usr_name = mysql_real_escape_string($_REQUEST['usr_name']);

to avoid a few problems with SQL Injection. But when I my string back from the function, I end up with nothing.

Also I keep getting this weird warning in my PHP log:

PHP Warning:  mysql_real_escape_string() [<a href='function.mysql-real-escape-string'>function.mysql-real-escape-string</a>]: A link to the server could not be established in /hermes/bosweb/web279/b2798/ipw.bankingforms/public_html/formAckResponse_controller.php on line 39

The host uses: PHP Version 4.4.7

Answer 1

From PHP.net:

Note: A MySQL connection is required before using mysql_real_escape_string() otherwise an error of level E_WARNING is generated, and FALSE is returned. If link_identifier isn't defined, the last MySQL connection is used.

In other words, you will have needed to connect to the MySQL database through mysql_connect() or mysql_pconnect() before you can use this function.