[jacquesm]

Once upon a time there was this thing called 'cfront'. Cfront took C++ and turned it into C which you then fed through your compiler.

At that time mixing C and C++ was trivial, especially because C++ was still quite simple and the C compiler was the target.

But after that things got more complicated. C evolved, several times in fact since that time and the C++ standard evolved as well. Leading to the impression that C and C++ are merely the old and the improved version of C but it is probably much better to think of them as two distinct species that share a common ancestor, where one of the two had some very radical mutations.

[loeg]

It would be relatively easy for C++ to add some kinds of C compatibility, and they just haven't bothered to. (E.g., the "static" keyword for parameter array sizes.) It's a little annoying for shared headers that have to be used in C and C++ programs.