C++ array of a self-defined class, no matching function call

问题

I was building a Huffman coding tree and I wanted to create an array where each position contains a separate tree, as the code follows:

// Number of initial nodes
int number;
cin >> number;
int* weights = new int[number];

for (int i = 0; i < number; i++) 
    cin >> weights[i];

// Convert to huffman tree with one element
intHuffTree* tree = new intHuffTree[number];
for (int i = 0; i < number; i++) {
    tree[i] = intHuffTree(weights[i]);
}

where the class is defined like:

// Huffman tree with integers
class intHuffTree {
private:
    // Root of the tree
    intHuffNode* Root;

public:
    // Leaf constructor
    intHuffTree (int freq) { Root = new intLeafNode(freq); }

    // Internal constructor
    intHuffTree (intHuffTree* l, intHuffTree* r) {
        Root = new intIntlNode(l->root(), r->root());
    }

    // Destructor
    ~intHuffTree() {};

    // Get root
    intHuffNode* root() { return Root; }

    // Root weight
    int weight() { return Root->weight(); }
};

When compiling, I got errors like:

main.cpp: In function ‘int main()’:
main.cpp:19:47: error: no matching function for call to ‘intHuffTree::intHuffTree()’
     intHuffTree* tree = new intHuffTree[number];
                                               ^

I wonder why I could not initialize the array as I did for the int array, and is there any possible solution?

Thanks a lot!

回答1:

intHuffTree* tree = new intHuffTree[number];

The above statement is creating an array of intHuffTree. The array would have 'number' elements. Each element would be of type intHuffTree. To create each element the compiler needs the default constructor which is missing in your code because you have provided overloaded constructors.

If you intend to create a single tree with 'number' elements you need to write it as

intHuffTree* tree = new intHuffTree(number);

If you intend to create an array of 'number' elements of intHuffTree you need to add the constructor with no arguments.

intHuffTree () { /* Do the right things here. */ }

回答2:

Take your code:

new intHuffTree[number];

What this is saying is "create N intHuffTrees using its default constructor", where N is number. You don't have a default constructor, which is what the error message is trying to tell you.

Looking at your code, perhaps you intended to pass number to the constructor instead? In which case, the code would be:

new intHuffTree(number);

Note that change in brackets.

回答3:

This

intHuffTree* tree = new intHuffTree[number];

attemps to allocate an array with number elements. To do so, a default constructor would be called (one that can be called without parameters), but your class has none.

When you don't need to deal with manual dynamic memory, then don't. To create an instance you could write