Can I set a default argument from a previous argument?

Question

Is it possible to use previous arguments in a functions parameter list as the default value for later arguments in the parameter list? For instance,

void f(         


        

Answer 1

No, that is not legal C++. This is specified in section 8.3.6/9 of the C++ Standard:

Default arguments are evaluated each time the function is called. The order of evaluation of function arguments is unspecified. Consequently, parameters of a function shall not be used in default argument expressions, even if they are not evaluated.

and:

int f(int a, int b = a); // error: parameter a used as default argument

And C89 at least does not support default parameter values.