[SOLVED] Why does ini_set() not override PHP settings?

I am trying to upload larger files so I set this in PHP code:

ini_set('upload_max_filesize', '1000M');
ini_set('post_max_size', '1100M');
ini_set('memory_limit', '1200M');

but $_POST and $_FILES are empty. But when I change php.ini settings it works. Why it doesn't change setting on the fly?

It's too late to have those settings changed after PHP has started.

upload_max_filesize - uploads happen before the PHP script runs and your ini_set() is executed
post_max_size - likewise

And even if you could change memory_limit (depends on server configuration), it would be too late again if you expect that big of an upload.