Constructor Overloading in C++

Question

My C++ overloading does not act as I assume it should:

#include "Node.h" #include <iostream>  Node::Node() {     cout << "1" << endl;     Node(Game(), 0.0); }  Node::Node(double v) {     cout << "2" << endl;     Node(Game(),v); }  Node::Node(Game g, double v) {     cout << "3" << endl;     numVisits = 0;     value = v;     game = g; } 

And the output from:

Node n(16); cout << n.value << endl; 

is 0, when it should be 16.

What am I doing incorrectly?

Answer 1

Node(Game(),v); in your constructor doesn't do what you expected. It just creates a temporary without using it and makes no effect. Then it immediately destructs that temporary when control flows over the ;.

The correct way is initializing the members in each constructor. You could extract their common code in a private init() member function and call it in each constructor like the following:

class Foo {     public:         Foo(char x);         Foo(char x, int y);         ...     private:         void init(char x, int y); };  Foo::Foo(char x) {     init(x, int(x) + 3);     ... }  Foo::Foo(char x, int y) {     init(x, y);     ... }  void Foo::init(char x, int y) {     ... }  

C++11 will allow constructors to call other peer constructors (known as delegation), however, most compilers haven't supported that yet.

Answer 2

The feature you're trying to use is called delegating constructors, which is part of C++0x. Using that syntax your second constructor becomes

Node::Node(double v) : Node(Game(),v) {     cout << "2" << endl; }