avoiding sql injection

plz i want to ask how to avoid sql injection
as when i make a text field and user enter a data
i want to be sure that my script is secure
it is a script that read from a database and write in other database
user can register
i am afraid any hacker do any hacking
--------
so question is how to make user enter data and i am sure it will not make any injection
i heard that there is functions as addslashes and strip slashes

can u help me in how to use them? or by any other thing for security?

 

php.net/htmlspecialchars
php.net/strip_tags
php.net/mysql_escape_string
php.net/htmlentities

^^read

 

strip tags is actually unnecessary.

With SQL injections it's as simple as applying mysql_real_escape_string before passing the data to the query

 

http://kzzen.com/2008-10-protect-your-website-against-rfi-attack-and-sql-injection.html#sql_injection