What are the differences between require and include, include_once and require_once?

Question

I use the pretty large Library PHP Image Workshop (http://phpimageworkshop.com/) at my project. It is about 75,5 KB. Everything works fine but if I try to include a 15 KB file with country codes, it fails. With the other files I easily get over 100 KB inclusion size, so my question; Is there a size limitation for include?

Answer 1

require will throw a PHP Fatal Error if the file cannot be loaded. (Execution stops)
VS
include produces a Warning if the file cannot be loaded. (Execution continues)

The require_once() statement is identical to require() except PHP will check if the file has already been included, and if so, not include (require) it again.
VS
The include_once() statement is identical to include() except PHP will check if the file has already been included, and if so, not include (require) it again.