Fail to understand what the difference is.
When should i use which?

essentially, there is no difference. With "include", if the file being included is not found proccessing continues without error. If you use "require" and the file is not found, your PHP script will get a 'fatal error' and all proccessing will stop.

I have found that are some other differences in include() vs require()

include() = more resource hungry with heavy server load and low memory
require() = much much less load on the server

here is an example, include() reads the php and evaluates it, require just dumps that bit of code into your page that required it and evals all at the same time.

Imagine you have 5 include on a page, php looks like it does the following...
include1() ... reads ... evals
include2() ... reads ... evals
include3() ... reads ... evals
include4() ... reads ... evals
include5() ... reads ... evals

whereas require dumps all 5 into the main php file and then evals all the code in one go. Imagine you have a few hundred users all simultaneously loading php pages with these includes, you wouldn't really notice except if you try to then load a larger flat file database or something else that may hit your memory with a heavy load at the same time. with the include() you will see it will take a lot lot longer to load the flat file, switch them to requires and your load time will drop dramatically.

I am still trying to think of an instance where you would want to use include over require... I havent yet.

just some observations...

Originally Posted by chadsmith76

I have found that are some other differences in include() vs require()

include() = more resource hungry with heavy server load and low memory
require() = much much less load on the server

here is an example, include() reads the php and evaluates it, require just dumps that bit of code into your page that required it and evals all at the same time.

Imagine you have 5 include on a page, php looks like it does the following...
include1() ... reads ... evals
include2() ... reads ... evals
include3() ... reads ... evals
include4() ... reads ... evals
include5() ... reads ... evals

whereas require dumps all 5 into the main php file and then evals all the code in one go. Imagine you have a few hundred users all simultaneously loading php pages with these includes, you wouldn't really notice except if you try to then load a larger flat file database or something else that may hit your memory with a heavy load at the same time. with the include() you will see it will take a lot lot longer to load the flat file, switch them to requires and your load time will drop dramatically.

I am still trying to think of an instance where you would want to use include over require... I havent yet.

just some observations...

Where did you find this information? I don't believe this is the case at all and I belive both actions do the exact same thing.

The only difference that I know they have have is that include will only throw a warning on failure and require will cause a fatel error on failure and actually will cause the PHP parse engine to stop and the script dies.

I use require on my core script files and include with files that won't break the script flow.