Q:ifdef type of functionality?

I'm new to PHP so please exscuse me if
this topic has gone round n round.

I am wondering if there is any way of
finding out if a file has been previously
required(). For example, require() some class
source code in two other class source code
files.

I thought of using some time of __FILE__
but I don't think this is correct.

Thanks for any help in advance,
mAk

I had the same problem... my solution was to set a variable at the end of the included or required file, and check if the variable is set before re-requiring it.