[Dev-C++] Directory Parsing

I'm trying to delve into more complex C programming. 
I want to know how to use io.h (linked to by dir.h)
for functions such as findfirst and so on with the
purpose of creating programs that can search for files
or perhaps perform like ls/dir.  I have found a few
examples that work.  One is Windows API, but I'm not
trying to do this with Windows API.  The other uses
dirent.h.  I've heard that this sort of thing is very
compiler/OS specific, so once I have this figured out
for GCC, there shouldn't be anymore problems.  I am
slightly confused on how to declare and deal with the
struct involved.  

Finally, how easily would this directory parsing
routine port to another OS or processor.  

I'd appreciate any advice.  Thanks.