Converting C++ to C

[perryh at pluto.rain.com]

Some early implementations of C++ operated as preprocessors
that emitted C code.  Is there any current tool that will do
that?  I didn't recognize any such option in the g++ manpage,
although I suppose it's possible that one of the -fdump-tree-
options would come close enough.

Reason:  I want to make what I think would be a fairly minor
change to a small (1100-line) C++ program, but I don't know C++
-- only C -- and I don't understand the program well enough
to mess with it.  I suspect I would be able to figure out an
equivalent C program.

In case it matters, I'm using FreeBSD 8.1.