Return void type in C and C++

Question

This compiles without any warnings.

Is this legal in C and C++ or does it just work in gcc and clang?

If it is legal, is it some new thing after C99?

Answer 1

Standard C does not support this construction:

C11 6.8.6.4: The return statement

Constraints

1 A return statement with an expression shall not appear in a function whose return type is void. A return statement without an expression shall only appear in a function whose return type is void.

No special provisions are added for the special case in the question. Some C compilers do support this as an extension (gcc does, unless instructed to conform to one of the C Standards), but C11 and previous versions consider it a constraint violation.