C conditional operator ('?') with empty second parameter

Question

(This question already has answers here): question from:https://stackoverflow.com/questions/10143125/c-conditional-operator-with-empty-second-parameter

Answer 1

It is not permitted by the language C (as far as I know), but compilers such as gcc have the shortcut a?:c as an extension. a?:c means the same as a?a:c.