How to load lua extensions using C API?

[Newton Kim <babynewton73@...>]

I'm using lua 5.1.

I'm making runtime engine that runs lua script.

I want the lua is ready with my extensions when it is instantiated.

(just as math or file is ready when the script is loaded)

But, I don't want to touch the source code.

I read the reference manual but failed.

What C API should I call to let the lua engine load my extension?

Thank you in advance.