PHP when to use filter_var instead of built in php functions

I noticed there are many things you can do with the PHP filter_var function which can also be done with other function.

For example, the filters FILTER_VALIDATE_REGEXP, FILTER_SANITIZE_ENCODED and many more also have their respective dedicated functions in PHP.

When should I use filter_var and when should I use the PHP functions? What are the advantages and disadvantages?

Solution

The advantage of the filter extension is that you have everything in one place.

But you are right, it doesn't provide much novel features. You could do most of the stuff with existing functions, in particular preg_replace or preg_match instead of FILTER_VALIDATE_REGEXP. Or typecasting, and using the normal htmlspecialchars instead of the filter option.

There is however filter_var_array, where one benefit becomes apparent. You can filter loads of variables per config. And you can predefine a list of filters to apply all at once:

$_POST = filter_var_array($_POST, array(
    "text" => FILTER_SANITIZE_ENCODED,
    "id" => FILTER_VALIDATE_INT,
    "title" => FILTER_SANITIZE_ENCODED,
));

I admit that's basically a triggered magic_quotes example, but you get the picture. Unification.