Yes, I have. I do it too, even some basic functions, I would look up on SO.

You really just need to know that there's a way to open files in C.

I don't think you can reach any sort of scale of breadth or depth if you try to memorize things. Programmers have to glue together a million things, it's just not realistic for them to know all the details of all of them.

It's unfortunate for the guy who has memorized all of K&R, but we have tools now to bring us these details based on some keywords, and we should use them.