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
– NathanOliver, Commented Sep 15, 2022 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
– user17732522, Commented Sep 15, 2022 at 13:13
Refer to how to ask where the first step is to "search and then research" and you'll find plenty of related SO posts for this. — Richard
– Richard, Commented Sep 15, 2022 at 13:15
And if your introductory book doesn't explain how to write default constructors, get a better one — Useless
– Useless, Commented Sep 15, 2022 at 13:16

Richard · Accepted Answer · 2022-09-15 13:21:12Z

3

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.

answered Sep 15, 2022 at 13:21

Richard

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