The protected keyword is a member access modifier. A protected member is accessible from within the class in which it is declared, and from within any class derived from the class that declared this member.

A protected member of a base class is accessible in a derived class only if the access takes place through the derived class type. For example, consider the following code segment:

class A 
{
   protected int x = 123;
}

class B : A 
{
   void F() 
   {
      A a = new A();  
      B b = new B();  
      a.x = 10;   // Error
      b.x = 10;   // OK
   }
}

The statement a.x =10 generates an error because A is not derived from B.

Struct members cannot be protected because the struct cannot be inherited.

It is an error to reference a protected member from a class, which is not derived from the protected member's class.

For more information on protected members, see 3.5.3 Protected access for instance members.

For a comparison of protected with the other access modifiers, see Accessibility Levels.

Example

In this example, the class MyDerivedC is derived from MyClass; therefore, you can access the protected members of the base class directly from the derived class.

// protected_keyword.cs
using System;
class MyClass 
{
   protected int x; 
   protected int y;
}

class MyDerivedC: MyClass 
{
   public static void Main() 
   {
      MyDerivedC mC = new MyDerivedC();

      // Direct access to protected members:
      mC.x = 10;
      mC.y = 15;
      Console.WriteLine("x = {0}, y = {1}", mC.x, mC.y); 
   }
}

Output

x = 10, y = 15

If you change the access levels of x and y to private, the compiler will issue the error messages:

'MyClass.y' is inaccessible due to its protection level.
'MyClass.x' is inaccessible due to its protection level.

See Also

C# Keywords | Access Modifiers | Accessibility Levels | Modifiers | 3.5.1 Declared accessibility