PHP $_GET security, $_POST security best practice

Question

It's a well covered topic, but I'd like to get some confirmation on methods of using data from user variables, in a few different situations.

1. The variable is never used in a database, never stored, only displayed on screen for the user. Which function to use to make sure no html or javascript can screw things up?

2. The variable is taken into the database, and used in SQL queries.

3. The variable does both.

At the moment I xss_clean, and strip_tags. I've always done this, just by autopilot. Is there a better technique? Apologies if there's an identical question out there. I kinda assume there is, although I couldn't find one as thorough as this.

Cheers.

Answer 1

1. Use the appropriate function while outputting, in HTML context, this is htmlspecialchars
2. Use prepared statements
3. See 1. and 2. – depending on whether you are displaying the variable or you are using it in a query.