Visual Studio 2010

Inheritance – Shape hierarchy

Necessary skills: Class inheritance, Member function overriding (virtual functions), Dynamic binding, Multiple classes (separate source and header files), C++ Standard Library string, iostream, iomanip, stringstream classes


In this assignment, you’ll create a hierarchy of C++ classes representing various shapes (eg. circle, rectangle, square). Each class will have its own .cpp source file and .h header file..

For the Shape class hierarchy, create an abstract Shape class that will be the base class of all the other shapes. It should have one private std::string instance variable representing the shape’s color, and should have the following public member functions:

Shape(const string& color) – a constructor that sets the color instance value.
string getColor() – a const member function returning the object’s color value.
double area() – a const pure virtual member function that computes and returns the object’s area. It must be overridden in each derived class.
string toString() – a const pure virtual member function that returns the shape’s description (color, type, measurements, and area) as a std::string. It must be overridden in each derived class. See the example output below for the format.
Create a Circle class that is derived from Shape. It should have one private double instance variable representing the radius, and should have the following public member functions:

Circle(const string& color, double radius) – a constructor that invokes the base Shape constructor (passing the color), then sets it’s own radius instance value.
double area() – this overriding member function computes and returns the Circle object’s area value.
string toString() – this overriding member function returns the Circle object’s description (color, type, measurements, and area).
Create a Square class with one private double instance variable representing the side length, with a constructor and overriding member functions for area() and toString().

Create a Rectangle class with double instance variables representing the width and length, with a constructor and overriding member functions for area() and toString().

Each derived class .h header file should #include the base Shape.h header. Each derived class .cpp source file should #include its header (e.g. Circle.cpp has a #include Circle.h), plus the other header files needed (eg. iomanip, strstream)

Each derived class constructor must use the constructor initializer syntax to call the base Shape constructor with the color parameter.

Derived classes do not provide a member function override for getColor(). The base Shape class implementation is inherited.

All character data is held using std::string from the C++ Standard Library (no char* or char arrays).

All toString() methods use a local std::ostringstream object to format the output (using manipulators) using output stream syntax (<< insertion operators), and return the string contents of the ostringstream. These methods do not write any output, just return the formatted string (as shown below in the example) – the main program does the actual output of the string. The toString() methods will call their area() methods to obtain the area value to be formatted.


For reading shape data, create a getShape.cpp file containing a getShape() function that returns a base Shape * pointer. It should read a shape description from an input stream, create the correct type of derived shape with the new operator and parameters to the constructor, and return a base Shape * pointer to the new object. After reading a shape color and type (e.g. blue circle), it reads the additional information specific to that type of shape (e.g. for a circle, it reads the radius), and then uses the new operator to create the specific derived type of shape (e.g. new Circle(color, radius) )

Input can be from cin, or from a stream input file (use iostreams). When there is no more input data (or when ‘done’ is entered), return a NULL Shape pointer. All character data is kept in C++ strings (no char[] arrays).

This is the only file that #includes the Circle.h, Square.h, and Rectangle.h header files (since it needs them to create the various types of shapes with the new operator).


The main.cpp file contains the main() function. It defines an array of base Shape pointers, and loops calling getShape() and storing the returned Shape pointer into the next available element of the array. The loop completes when a NULL Shape pointer is returned from getShape.

Note that the array contains pointers that point to a variety of derived shape objects (circles, squares, rectangles). This is possible because of the IS-A public inheritance relationship (e.g. a Circle IS-A Shape, and thus has all the properties and behaviors of a Shape).