Silly question about C++

["Marco Contenti" <m contenti libero it>]

Browsing through the Dia code I found lots of objects, methods, properties,
subclassing... all coded in C.
The first thing I thought is that all this could have been a lot easier to
write and maintain, more reliable and efficient if the project started with
C++.
Is there some basic requirement that prevents using C++?
Please don't tell me that the project started too early. I've been using C++
for 13 years.
Cheers.
Marco