When Are Constructors Called?

When a derived class object is created, whose constructor is executed first? The one in the derived class or the one defined by the base class? For example, given a derived class called B and a base class called A, is A’s constructor called before B’s, or vice versa? The answer is that in a class hierarchy, constructors are called in order of derivation, from base class to derived class. Furthermore, this order is the same whether or not base is
used. If base is not used, then the default (parameterless) constructor of each base class will be executed. The following program illustrates the order of constructor execution:

Example

using System;

namespace ConsoleApplication1
{
    // Create a base class.
    class A
    {
        public A()
        {
            Console.WriteLine("Constructing A.");
        }
    }
    // Create a class derived from A.
    class B : A
    {
        public B()
        {
            Console.WriteLine("Constructing B.");
        }
    }
    // Create a class derived from B.
    class C : B
    {
        public C()
        {
            Console.WriteLine("Constructing C.");
        }
    }
    class OrderOfConstruction
    {
        static void Main()
        {
            C c = new C();
        }
    }
}

Output

Constructing A.
Constructing B.
Constructing C.