C++ Constructor Not Called

Calling constructors in c++ without new

Both lines are in fact correct but do subtly different things.

The first line creates a new object on the stack by calling a constructor of the format Thing(const char*).

The second one is a bit more complex. It essentially does the following

1. Create an object of type Thing using the constructor Thing(const char*)
2. Create an object of type Thing using the constructor Thing(const Thing&)
3. Call ~Thing() on the object created in step #1

Constructor is not called in C++

The constructor of your Order class will get callled.

Item items[20];  // <-- here you actually create 20 Items and the constructor for each Item will be called. Then the Order Constructor will get called.

You could use std::list<Item> items; instead of Item items[20]. In that case you don't actually create an Item (and therefore its constructor will not get called) you just create a container where you can store your items.

Anyway, it is bad practice to do what you do in your constructor. A constructor should initialize the object and it should run fast. So create a method instead.

C++ constructor not called

Car o1(Car());

This declares a function called o1 that returns a Car and takes a single argument which is a function returning a Car. This is known as the most-vexing parse.

You can fix it by using an extra pair of parentheses:

Car o1((Car()));

Or by using uniform initialisation in C++11 and beyond:

Car o1{Car{}};

But for this to work, you'll need to make the parameter type of the Car constructor a const Car&, otherwise you won't be able to bind the temporary to it.

Why is the copy constructor not called?

Whenever a temporary object is created for the sole purpose of being copied and subsequently destroyed, the compiler is allowed to remove the temporary object entirely and construct the result directly in the recipient (i.e. directly in the object that is supposed to receive the copy). In your case

MyClass MyObj(MyClass(1, 2));

can be transformed into

MyClass MyObj(1, 2);

even if the copy constructor has side-effects.

This process is called elision of copy operation. It is described in 12.8/15 in the language standard.

c# Constructor not called

Change

public Coordinate invalid = new Coordinate(-1, -1);

To

public static Coordinate invalid = new Coordinate(-1, -1);

public Coordinate invalid = new Coordinate(-1, -1); causes stack overflow. that's because new Coordinate initialized inside Coordinate class so every time new coordinate must be created. Make the field static so that is created once and can be used for all instances.

You can also add readyonly keyword if the reference is not supposed to change.

public readonly static Coordinate invalid = new Coordinate(-1, -1);

C++ default Constructor not being called

 Circle c2();

Does not create an object, it declares a function by name c2 which takes no argument and returns a Circle object. If you want to create a object just use:

Circle c2;

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