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copied!<p>A constructor is a function with the same name as the class. The main purpose of a constructor is to initialize member variables of a newly-created object to some default values. It might also call other initialization functions.<br> Just like other functions in C++, constructors can be overloaded. (An overloaded function is a new version of an existing function with different arguments). For example, consider the following <code>Point</code> class with three constructors:</p> <pre><code>class Point { public: Point() : x_(0), y_(0) { } Point(int x, int y) : x_(x), y_(y) { } Point(const Point& p) : x_(p.x), y_(p.y) { } private: int x_; int y_; }; </code></pre> <p>The first constructor initializes the co-ordinates to zero, while the second allows the user to specify their default values:</p> <pre><code>void create_and_destroy_points () { Point p1; // => x_ = 0, y_ = 0 Point p2(100, 200); // x_ = 100, y_ = 200 } </code></pre> <p>When declared that way, those <code>Point</code> objects are allocated on the <em>stack</em>. That means the memory allocated to them will be automatically released when the <code>create_and_destroy_points</code> function returns. In other words, <code>p1</code> and <code>p2</code> are of no use outside the function.<br> Objects can also be allocated on the <em>heap</em>. This allocates the objects at run time, and they can then survive across various function calls. They are allocated with the <code>new</code> keyword and continue to live until they are deallocated with <code>delete</code>. Failing to delete a heap allocated object after its use will lead to a <em>memory leak</em>.</p> <pre><code>Point* create_point () { Point* p = new Point(100, 200); return p; } Point* p = create_point(); // use p delete p; </code></pre> <p>The third constructor is a <em>copy constructor</em>. It is invoked when a new object is constructed by copying another object:</p> <pre><code>Point p1; Point p2 = p1; // calls the copy constructor for p2 with p1 as argument. Point p3(p1); // alternate syntax </code></pre>

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