C ++ default parameter for another parameter

Question

Is it possible to use the first default parameter for the second parameter, for example?

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

My compiler does not seem to like it, so this may not be allowed.

Answer 1

Your question has already been answered (this is not resolved), but in case you do not understand this, 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

Is not allowed.

The evaluation order of the function arguments is not specified. Therefore, function parameters should not be used in the default argument, even if they are not evaluated.

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

Answer 3

U,

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

But the value of b will not change after the function is executed. Passing b by reference will work. (int & b)