C99 Variadic macros, for one, which allows for a nice to use `foreach` implementation. As for the latest C spec, I use a set of C compilable by C++, since most of the functional tests back-test against the STL, and hence compile with a C++ compiler
#define foreach(container, variable, iterator) \
for (JOIN(container, it) iterator = JOIN(JOIN(container, it), each) (variable); \
!iterator.done; iterator.step(&iterator))
EDIT: Done, and thank you so much - it's so much cleaner this way
https://devblogs.microsoft.com/cppblog/c11-and-c17-standard-...