Another argument cannot be used as the default value. The standard states:
8.3.6 Default arguments
…
9 A default argument is evaluated each time the function is called with no argument for the corresponding
parameter. The order of evaluation of function arguments is unspecified. Consequently, parameters of a
function shall not be used in a default argument, even if they are not evaluated.
and illustrates it with the following sample:
int f(int a, int b = a); // error: parameter a
// used as default argument