sizeof empty structure is 0 in C and 1 in C++ why?

Question

(This question already has answers here): question from:https://stackoverflow.com/questions/3849334/sizeof-empty-structure-is-0-in-c-and-1-in-c-why

Answer 1

You cannot have an empty structure in C. It is a syntactic constraint violation. However gcc permits an empty structure in C as an extension. Furthermore the behaviour is undefined if the structure does not have any named member because

C99 says :

If the struct-declaration-list contains no named members, the behavior is undefined.

So

struct Empty {}; //constraint violation

struct Empty {int :0 ;}; //no named member, the behaviour is undefined.

And yes size of an empty struct is C++ cannot be zero :)