This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
Annex C lists C compatibility issues. One item not in the annex came up in a discussion in comp.std.c++.
Consider this C and C++ code:
const int j = 0; char* p = (char*)j;
Rationale (10/99): Because j is not a constant expression in C, this code fragment has implementation-defined behavior in C. There is no incompatibility with C resulting from the fact that C++ defines this behavior.