C23 finally relaxes that rule: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2510.pdf https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2510.pdf (although

C23 finally relaxes that rule: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2510.pdf https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2510.pdf (although some C compilers already allowed it in non-pedantic mode)