Comment by gary_0

In other words, C structs and C++ structs are not the same thing (although C++ can usually handle C structs too). C structs are Plain Old Data. C++ structs are "objects" and there are pages and pages of rules in the C++ Standard about what that means, and there's no way the C Standard can incorporate all that. And you can't drag any C++ struct/class features into C without dragging in all those rules with them.