C++ call of overloaded constructor is ambiguous

Question

Let's say I have this dummy class definition: ``` class Node { public: Node (); Node (const int = 0); int getVal(); private: int val; }; ``` And dummy constructor implementations for educational purposes only as well: ``` Node::Node () : val(-1) { cout << "Node:: DEFAULT CONSTRUCTOR" << endl; } Node::Node(const int v) : val(v) { cout << "Node:: CONV CONSTRUCTOR val=" << v << endl; } ``` Now, if I compile (with options: `-Wall -Weffc++ -std=c++11`) the code below: ``` #include <iostream> #include "node.h" using namespace std; int main() { Node n; return 0; } ``` I get this error, and does not compile at all: ``` node_client.CPP: In function ‘int main()’: node_client.CPP:10:16: error: call of overloaded ‘Node()’ is ambiguous Node n; ^ node_client.CPP:10:16: note: candidates are: In file included from node_client.CPP:4:0: node.h:14:5: note: Node::Node(int) Node (const int = 0); ^ node.h:13:2: note: Node::Node() Node (); ^ ``` I cannot understand why. As far as I know (I am learning C++),…

Accepted Answer

a call to Node::Node() should not be ambiguous with respect to Node::Node(const int) because the have a different parameter signature.

Sure that is ambiguous. Think twice!

You have

```
    Node ();
    Node (const int = 0);
```

which one should be selected when you call `Node()`?? The one with the defaulted value parameter?

It should work without providing the default:

```
    Node ();
    Node (const int); // <<<<<<<<<<<<< No default
```

C++ call of overloaded constructor is ambiguous

Solution

Problem