CODEWITHSUNDEEP
c++parameters
Bernard
Bernard

Reputation: 5666

C++ default a parameter to another parameter

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.

Upvotes: 4

Views: 757

Answers (3)

Benjamin Lindley
Benjamin Lindley

Reputation: 103693

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);
}

Upvotes: 12

Jingning Zhang
Jingning Zhang

Reputation: 1

if I were U I would do this

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

But the b value is not gonna change after the function complete executing. Passing b by reference will work. (int &b)

Upvotes: -5

Brian Bi
Brian Bi

Reputation: 119089

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)

Upvotes: 9

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