Not quite. Gcc it didn't fold it during preprocessing for a fully constant expression, which is allowed. In which case always sizeof(void) is a valid answer. W

Not quite. Gcc it didn't fold it during preprocessing for a fully constant expression, which is allowed. In which case always sizeof(void) is a valid answer. Which is a compile error. That is at least what C99 draft seems to say. I'll check C11 draft next. Edit: same.