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Designing a base class and subclasses, and their extension, in C++

My first technical post for 2015 - looking back at some of last year's new C++ examples.

Oh - OK - I'm writing this on 1st January and these examples were written and uploaded yesterday, so they're nothing like as old as it sounds.

On Monday and Tuesday, I wrote classes from scratch and looked at basic design - see [here]. I then added dynamic memory management via the new keyword for heap allocation, and using a vector to store references or pointers to my objects - see [here].

Yesterday, I wrote an example in which in had a base class that contained the common specifications and code for a number of similar types of objects, andthen looked at how that can be extended to provide similar types of objects without code duplication. For the whole course, I was very much stressing Test Driven Development and Behaviour Driven Development, and so my very first piece of code - [here] - provides a test and a specification of the API (application programmer interface) to ensure it compiles. It won't load into a complete program yet.

In the second example - [here] - I have implemented the base class (called "shape") and the subclasses ("ball" and "box") together with "cube" which further derives from "shape". You'll notice how hardly any code is repeated from one section to another, as the common code is shared as far up the tree as possible. Colour and density don't change with the change of shape, so they're in the common code, whereas the volume does change for a ball and a box. The volume for a cube is simply the volume for a box, as a cube (by our definition) is simply the special case of a box.

When working out whether incoming data (from a file, for example) relates to boxes, cubes or balls, some logic is required. Naturally, that logic falls within the class code which is looked after by our data type programmer, rather than by our application programmer who just wants to say "here is some data - please work out what object type it is and make the object for me". I have provided a solution to this requirement in the next program - [here] via a static (class) method called "factory"). Nothing special in that name - it's just a convention as raw material is passed in (an incoming string, for example) and manufactured produce (or, rather, and object) is returned.

Further testing was added in the next stage, using the text harness from previous days ([here] for the code [here] for the test harness headers and [here] for the test harness code. And the final example [here] shows operator overloading in C++ ... that may not have been a logical extenion to my demonstration, but it's a subject needed to be covered on our C++ courses and it fitted in here during the presentation.
(written 2015-01-01)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Q909 - Object Orientation and General technical topics - Object Orientation: Composite Objects
  [4450] Deciding whether to use parameters, conditional statements or subclasses - (2015-03-05)
  [4394] Philosophy behind object design - and how I applied in to a Java example - (2015-01-14)
  [3979] Extended and Associated objects - what is the difference - C++ example - (2013-01-18)
  [3609] How do classes relate to each other? Associated Classes - (2012-02-12)
  [3251] C++ - objects that are based on other objects, saving coding and adding robustness - (2011-04-17)
  [3152] Jargon busting - (2011-01-30)
  [3142] Private and Public - and things between - (2011-01-22)
  [2922] Getting the OO design write - with PHP a example - (2010-08-14)
  [2865] Relationships between Java classes - inheritance, packaging and others - (2010-07-10)
  [2641] Object Oriented Programming in PHP - (2010-02-19)
  [2170] Designing a heirarcy of classes - getting inheritance right - (2009-05-11)
  [1348] Screw it or Glue it? Access to Object variables - a warning - (2007-09-12)
  [1345] Perl and Shell coding standards / costs of an IT project - (2007-09-11)
  [592] NOT Gone phishing - (2006-02-05)
  [477] Class, static and unbound variables - (2005-10-25)

Q908 - Object Orientation and General technical topics - Object Orientation: Design Patterns
  [4673] Separating detailed data code from the main application - Ruby example - (2016-05-16)
  [4663] Easy data to object mapping (csv and Python) - (2016-03-24)
  [4626] Singleton design pattern - examples and uses - (2016-01-20)
  [4581] Thin application, thick objects - keep you main code simple. Example in Ruby - (2015-11-21)
  [4421] How healthy are the stars of stage and screen? - (2015-02-09)
  [4396] Java Utility class - flexible replacement for array. Also cacheing in objects and multiple catch clauses example. - (2015-01-16)
  [4359] How to avoid too many recalculations within an object - (2014-12-21)
  [4356] Object factories in C++, Python, PHP and Perl - (2014-12-19)
  [4330] Java - factory method, encapsulation, hashmap example - (2014-11-27)
  [4325] Learning to program - what are algorithms and design patterns? - (2014-11-22)
  [4098] Using object orientation for non-physical objects - (2013-05-22)
  [4096] Perl design patterns example - (2013-05-20)
  [4021] Spike solution, refactored and reusable, Python - Example - (2013-02-28)
  [3843] Caching Design Patterns - (2012-08-20)
  [3810] Reading files, and using factories to create vectors of objects from the data in C++ - (2012-07-21)
  [3716] Learning C++ - a design pattern for your first class - (2012-05-02)
  [3608] Design Patterns - what are they? Why use them? - (2012-02-12)
  [2977] What is a factory method and why use one? - Example in Ruby - (2010-09-30)
  [2741] What is a factory? - (2010-04-26)
  [2322] Looking for a practical standards course - (2009-08-05)
  [1224] Object Relation Mapping (ORM) - (2007-06-09)
  [485] North, Norther and Northest - PHP 5 Objects - (2005-11-04)

C233 - C and C based languages - OO in C++ - beyond the basics
  [4560] Variables, Pointers and References - C and C++ - (2015-10-29)
  [4559] When do I use the this keyword in C++? - (2015-10-29)
  [4375] Final examples for 2014 - and a look at our 2015 training course options - (2014-12-31)
  [3811] Associated Classes - using objects of one class within another - (2012-07-21)
  [3508] Destructor methods in C++ - a primer - (2011-11-05)
  [3244] C and C++ - preprocess, compile, load, run - what each step is for - (2011-04-12)
  [3124] C++ - putting the language elements together into a program - (2011-01-08)
  [3123] C++ objects - some short, single file demonstrations - (2011-01-07)
  [3056] C++ - a complete example with polymorphism, and how to split it into project files - (2010-11-16)
  [2845] Objects and Inheritance in C++ - an easy start - (2010-07-01)
  [2577] Complete teaching example - C++, inheritance, polymorphism - (2010-01-15)
  [1819] Calling base class constructors - (2008-10-03)
  [1674] What a lot of files! (C++ / Polymorphism demo) - (2008-06-12)
  [1572] C - structs and unions, C++ classes and polymorphism - (2008-03-13)
  [1217] What are factory and singleton classes? - (2007-06-04)
  [925] C++ - just beyond the basics. More you can do - (2006-11-14)
  [831] Comparison of Object Oriented Philosophy - Python, Java, C++, Perl - (2006-08-13)
  [801] Simple polymorphism example - C++ - (2006-07-14)
  [798] References and Pointers in C++ - (2006-07-10)

C234 - C and C based languages - Further C++ Object Oriented features
  [4366] Changing what operators do on objects - a comparison across different programming languages - (2014-12-26)
  [3982] Using a vector within an object - C++ - (2013-01-19)
  [3509] Operator Overloading, Exceptions, Pointers, References and Templates in C++ - new examples from our courses - (2011-11-06)
  [3430] Sigils - the characters on the start of variable names in Perl, Ruby and Fortran - (2011-09-10)
  [3238] Bradshaw, Ben and Bill. And some C and C++ pointers and references too. - (2011-04-09)
  [3069] Strings, Garbage Collection and Variable Scope in C++ - (2010-11-25)
  [3057] Lots of things to do with and within a C++ class - (2010-11-16)
  [2849] What are C++ references? Why use them? - (2010-07-02)
  [2717] The Multiple Inheritance Conundrum, interfaces and mixins - (2010-04-11)
  [2673] Multiple Inheritance in C++ - a complete example - (2010-03-12)
  [2576] What does const mean? C and C++ - (2010-01-15)
  [2005] Variables and pointers and references - C and C++ - (2009-01-23)
  [2004] Variable Scope in C++ - (2009-01-22)
  [1159] It can take more that one plus one to get two. - (2007-04-22)
  [802] undefined reference to typeinfo - C++ error message - (2006-07-15)


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What FGW passengers want to talk about / and PHP programming to find out
Designing a base class and subclasses, and their extension, in C++
Well House Consultants, Well House Manor, First Great Western Coffee shop, TransWilts / 2014 web site reports
Test driven development, and class design, from first principles (using C++)
A long and disappointing evening
Template / design pattern for C++ constructor and accessors
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