What is the purpose of base constructors

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What is the purpose of calling a base constructor when creating a constructor for a derived class?

Example:

C#

class Manager : Employee
    {
        public Manager()
            :base()
        {
            
        }

Posted 15-Feb-14 7:46am

ProjectDreamer

Updated 15-Feb-14 7:55am

Nelek

v2

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3 solutions

Solution 1

A base constructor allows common initialization code to be executed when a derived class is constructed. You explicitly call a base constructor when you want to pass arguments to it when the derived class is being constructed. For example:

C#

public class MyException : Exception
{
    public MyException
        (string message,
         object data) : base (message)
    {
        // Common initialization comes here
        ...
    }
}

/ravi

Posted 15-Feb-14 8:37am

Ravi Bhavnani

Comments

Sergey Alexandrovich Kryukov 15-Feb-14 22:48pm

Correct, a 5.
However, you should have mentioned that in OP's code base() is totally redundant and would be automatically called.
—SA

Ravi Bhavnani 15-Feb-14 23:01pm

You're absolutely right, Sergey.

/ravi

Solution 3

base constructor is used for run base class methods

Posted 15-Feb-14 8:57am

Member 9425683

Comments

Sergey Alexandrovich Kryukov 28-Feb-14 14:08pm

Really? How interesting! Then please tell us: is it possible to call base class methods without the base constructor?
—SA

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Maarten Kools · Accepted Answer · 2014-02-15T08:46:00

In your example none. In this case Employee's constructor will automatically be called.

However, if you have a constructor with parameters, there is a purpose. Consider the following example:

C#

abstract class Foo
{
    protected Foo()
    {
    }

    protected Foo(int number)
    {
    }

    protected Foo(string s)
    {
    }
}

class Bar : Foo
{
    public Bar()
    {
        // Foo() is invoked automatically, since the call to the base constructor is omitted.
    }

    public Bar(int number)
        : base(number)
    {
        // Foo(int) is called, since it is explicitly invoked
    }

    public Bar(string s)
    {
        // Foo() is invoked automatically, since the call to the base constructor is omitted.
    }
}

If Foo does not have a default constructor (in my example it does), its constructor needs to be explicitly called. There will actually be a compiler error if you don't implement some constructor on Bar, and if you don't call the base constructor, there will be an error as well.

Bottom line, if you have a parameterless constructor in your base class, it will be automatically called if you don't explicitly specify it. And if you do not have a parameterless constructor, you have to call it from your derived class whether you want it or not.