Yes, several even, C++98 or C++11 code will not compile in C++26 mode, depending if some of those feature were being used. Exception specifications, auto_ptr,

Yes, several even, C++98 or C++11 code will not compile in C++26 mode, depending if some of those feature were being used. Exception specifications, auto_ptr, C++11 GC, the way volatile works, uninitialised variables,...