The parameter parmN is the identifier of the rightmost parameter in the variable parameter list of the function definition. If parmN is declared with the register storage class, with a function or array type, or with a type that is not compatible with the type that results after application of the default arguments promotions, the behavior is undefined. Expands to an expression that has the type and value of the next argument in the call.
Successive invocations return the values of the remaining arguments in turn.