grd grd - 1 month ago 18
C++ Question

C++ call of overloaded constructor is ambiguous

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

There is something I am missing: What it is?

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
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