C++ default a parameter to another parameter

Question

Can I use the first parameter as a default for the second parameter, like this?

int do_something(int a, int b = a + 1){
    /* ... */
}

My compiler doesn't seem to like it, so perhaps it's not allowed.

Answer 1

Your question has already been answered (it is not allowed), but in case you didn't realize, the workaround is trivial with function overloading.

int do_something(int a, int b){
    /* ... */
}

int do_something(int a) {
    return do_something(a, a + 1);
}

Answer 2

It is not allowed.

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.

(from [dcl.fct.default]/9 in C++14)