C# 0 The Complete Reference

Triangle

’s constructor initializes the members of 

TwoDShape

 that it inherits along 

with its own 

Style

 field.

When both the base class and the derived class define constructors, the process is a 

bit more complicated because both the base class and derived class constructors must be 

executed. In this case, you must use another of C#’s keywords, 

base

, which has two uses. 

The first use is to call a base class constructor. The second is to access a member of the base 

class that has been hidden by a member of a derived class. Here, we will look at its first use.

Calling Base Class Constructors

A derived class can call a constructor defined in its base class by using an expanded form 

of the derived class’ constructor declaration and the 

base

 keyword. The general form of this 

expanded declaration is shown here:

derived-constructor

(

parameter-list

) : base(

arg-list

) {

   // body of constructor

}

Here, 

arg-list

 specifies any arguments needed by the constructor in the base class. Notice the 

placement of the colon.

To see how 

base

 is used, consider the version of 

TwoDShape

 in the following program. 

It defines a constructor that initializes the 

Width

 and 

Height

 properties. This constructor is 

then called by the 

Triangle

 constructor.

// Add constructor to TwoDShape.

using System;

// A class for two-dimensional objects.

class TwoDShape {

  double pri_width;

  double pri_height;

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