How to initialize the array-like member variable in the constructor?

Question

How to initialize the array-like member variable?

The visual studio code says:

no matching function for call to 'Node::Node()' gcc line 12 col 9

const int N = 100;

struct Node {
    int val, ch[2];
    /**
    void init(int _val) {
        this->val = _val, this->ch[0] = this->ch[1] = 0;
    }*/
    Node (int _val): val(_val) {
        this->ch[0] = this->ch[1] = 0;
    }
} tree[N];    // <--------- this is line 12


int main() {
    int a;
    cin >> a;
    tree[0] = Node(a);
}

The error is complaining about `tree[N]`, not `ch[2]`. Like the error says, you need to give your class a default constructor. If you don't want to do that, you need to specify an initializer for each array element. — NathanOliver, Sep 15 '22 at 13:12
Or simply use a `std::vector` with `push_back`/`emplace_back` instead of an array, which doesn't require you to immediately (default-)construct all elements. — user17732522, Sep 15 '22 at 13:13
Refer to [how to ask](https://stackoverflow.com/help/how-to-ask) where the first step is to *"search and then research"* and you'll find plenty of related SO posts for this. — Jason, Sep 15 '22 at 13:15
And if your introductory book doesn't explain how to write default constructors, get a [better one](https://stackoverflow.com/q/388242/212858) — Useless, Sep 15 '22 at 13:16

score 3 · Accepted Answer · answered Sep 15 '22 at 13:21

The problem is that when you wrote tree[N] you're creating an array whose elements will be default constructed but since there is no default constructor for your class Node, we get the mentioned error.

Also, Node doesn't have a default constructor because you've provided a converting constructor Node::Node(int) so that the compiler will not automatically synthesize the default ctor Note::Node().

To solve this you can add a default ctor Node::Node() for your class.

How to initialize the array-like member variable in the constructor?

1 Answers1