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The base keyword

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The base keyword is used to access members of the base class from within a derived class. Use it if you want to:

  • Call a method on the base class overridden by another method.
  • Specify which base-class constructor should be called when creating instances of the derived class.

The base class access is permitted only in a constructor, in an instance method, and in an instance property accessor. Using the base keyword from within a static method produces an error.

The base class that is accessed is the base class specified in the class declaration. For example, if you specify class ClassB : ClassA, the members of ClassA are accessed from ClassB, regardless of the base class of ClassA.

In this example, both the base class Person and the derived class Employee have a method named GetInfo. By using the base keyword, it's possible to call the GetInfo method of the base class from within the derived class.

public class Person
{
    protected string ssn = "444-55-6666";
    protected string name = "John L. Malgraine";

    public virtual void GetInfo()
    {
        Console.WriteLine($"Name: {name}");
        Console.WriteLine($"SSN: {ssn}");
    }
}
class Employee : Person
{
    public readonly string id = "ABC567EFG";
    public override void GetInfo()
    {
        // Calling the base class GetInfo method:
        base.GetInfo();
        Console.WriteLine($"Employee ID: {id}");
    }
}

class TestClass
{
    static void Main()
    {
        Employee E = new Employee();
        E.GetInfo();
    }
}
/*
Output
Name: John L. Malgraine
SSN: 444-55-6666
Employee ID: ABC567EFG
*/

This example shows how to specify the base-class constructor called when creating instances of a derived class.

public class BaseClass
{
    private int num;

    public BaseClass() => 
        Console.WriteLine("in BaseClass()");

    public BaseClass(int i)
    {
        num = i;
        Console.WriteLine("in BaseClass(int i)");
    }

    public int GetNum() => num;
}

public class DerivedClass : BaseClass
{
    // This constructor will call BaseClass.BaseClass()
    public DerivedClass() : base() { }

    // This constructor will call BaseClass.BaseClass(int i)
    public DerivedClass(int i) : base(i) { }

    static void Main()
    {
        DerivedClass md = new DerivedClass();
        DerivedClass md1 = new DerivedClass(1);
    }
}
/*
Output:
in BaseClass()
in BaseClass(int i)
*/

For more examples, see new, virtual, and override.

C# language specification

For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.

See also