Calling Base Class Members in Object oriented concept in C Language

Derived classes can access the members of their base class if those members have protected or greater access. Simply use the member name in the appropriate context, just as if that member were a part of the derived class itself. Here's an example:

abstract public class Contact
{
private string address;
private string city;
private string state;
private string zip;
public string FullAddress()
{
string fullAddress = address + '\n' + city + ',' + state + ' ' + zip;
return fullAddress;
}
}
public class Customer : Contact
{
public string GenerateReport()
{
string fullAddress = FullAddress();
// do some other stuff...
return fullAddress;
}
}

In above example, the GenerateReport() method of the Customer class calls the FullAddress() method in its base class, Contact. All classes have full access to their own members without qualification. Qualification refers to using a class name with the dot operator to access a class member-MyObject.SomeMethod(), for instance. This shows that a derived class can access its base class members in the same manner as its own.

More Tips regarding Inheritance:

A static member cannot be marked as override, virtual, or abstract. So following is an error:
public static virtual void GetSSN()
You can't call static methods of base class from derived class using base keyword.
In above example if you declare a static method as follows:
public class Person
{
protected string ssn = "444-55-6666";
protected string name = "John L. Malgraine";
public static void GetInfo()
{
// Implementation
}
}

now you can't call this method using base.GetInfo() from derived class instead you have to call Person.GetInfo() from derived class.

Inside Static members we can access only static fields, methods etc.
Following example will give error, because we can't access name in GetInfo() because name is not static.

public class Person
{
protected string ssn = "444-55-6666";
protected string name = "John L. Malgraine";
public static void GetInfo()
{
Console.WriteLine("Name: {0}", name);
Console.WriteLine("SSN: {0}", ssn);
}
}

Virtual or abstract members cannot be private.

 If you are not overriding a virtual method of base class in derived class, you can't use base class method by using base keyword in derived class. Also when you will create an instance of derived class, it will call derived class method and you will only be able to access base class method when you will create instance of base class.
You can't decrease access level of a method in derived class when you are overriding a base class method in derived class, vice versa is possible.
Means you can make protected method of base class to public in derived class.
The "this" keyword refers to:

the current instance for which a method is called. Static member functions do not have a this pointer. The this keyword can be used to access members from within constructors, instance methods, and instance accessors.
The following are common uses of this:
To qualify members hidden by similar names, for example:

public Employee(string name, string alias)
{
this.name = name;
this.alias = alias;
}

In above example, this.name refers to private variable name in the class. If we write name = name, then this will refer to argument name of the constructor Employee and not to private variable name in the class. In this case private variable name will never be initialized.

To pass an object as a parameter to other methods, for example:
CalcTax(this);
To declare indexers, for example:


public int this [int param]
{
get
{
return array[param];
}
set
{
array[param] = value;
}
}

It is an error to refer to this in a static method, static property accessor, or variable initializer of a field declaration.

In this example, this is used to qualify the Employee class members, name and alias, which are hidden by similar names. It is also used to pass an object to the method CalcTax, which belongs to another class.

// keywords_this.cs
// this example
using System;
public class Employee
{
public string name;
public string alias;
public decimal salary = 3000.00m;
// Constructor:
public Employee(string name, string alias)
{
// Use this to qualify the fields, name and alias:
this.name = name;
this.alias = alias;
}
// Printing method:
public void printEmployee()
{
Console.WriteLine("Name: {0}\nAlias: {1}", name, alias);
// Passing the object to the CalcTax method by using this:
Console.WriteLine("Taxes: {0:C}", Tax.CalcTax(this));
}
}
public class Tax
{
public static decimal CalcTax(Employee E)
{
return (0.08m*(E.salary));
}
}
public class MainClass
{
public static void Main()
{
// Create objects:
Employee E1 = new Employee ("John M. Trainer", "jtrainer");
// Display results:
E1.printEmployee();
}
}

Output
Name: John M. Trainer
Alias: jtrainer
Taxes: $240.00