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For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
C++ - unknown array size, unknown object type. Help!

There are time when you're writing a program where you say "I don't know".

• I don't know how many records / object I'm going to read from a data file into an array - so I can't set the size of my array

• I don't know what sort of object I'll be creating from a line I've read from a data file until I analyse it, so I can't call the constructor directly.

You could write a program to read take up to a certain maximum number of records / objects, but one day you'll find that someone want to run that program with more records than you've allowed for. The solution (C++ answer / term) is to use a vector - which is line an array or objects in many ways, but can dynamically expand. It saves you writing you own code with realloc calls.

And you could write a program which analyses incoming data lines before calling the appropriate constructor - but by doing so you're moving code which really should be in the class into each application. The solution is to provide a static method in the base class of all possible objects, which analyses the data and decides which constructor to call. Such a method is known as a factory method.

An example showing these techniques - from the C++ course I ran the week before last - is [here]. It also shows some file and string handling - a little bit of everything as I pulled together elements of the C++ language into a very straightforward application, but one covering many aspects.

I might not know how big my array should be, or what type of data each line will contain - but I do know that our next series of C and C++ courses starts at the very end of May - see [here]. If you've missed those, there are further courses in August, and in the autumn - use the same link as we'll update our page.

(written 2011-04-17)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
C239 - C and C based languages - Putting it all together
  [836] Build on what you already have with OO - (2006-08-17)
  [925] C++ - just beyond the basics. More you can do - (2006-11-14)
  [945] Code quality counts - (2006-11-26)
  [1181] Good Programming practise - where to initialise variables - (2007-05-09)
  [2646] Compile but do not run PHP - syntax check only - (2010-02-22)
  [2673] Multiple Inheritance in C++ - a complete example - (2010-03-12)
  [2674] Make and makefiles - a commented example to help you learn - (2010-03-12)
  [2851] Further C++ material - view new or old - (2010-07-04)
  [3067] Using C and C++ functions in the same program - how to do it - (2010-11-24)
  [3069] Strings, Garbage Collection and Variable Scope in C++ - (2010-11-25)
  [3810] Reading files, and using factories to create vectors of objects from the data in C++ - (2012-07-21)
  [4326] Learning to program - comments, documentation and test code - (2014-11-22)
  [4374] Test driven development, and class design, from first principles (using C++) - (2014-12-30)
  [4559] When do I use the this keyword in C++? - (2015-10-29)

C238 - C and C based languages - Templates
  [1478] Some new C programming examples - files, structs, unions etc - (2007-12-19)
  [3245] Collections in C and C++ - arrays, vectors and heap memory blocks - (2011-04-12)
  [3388] Templates in C++ - defining a family pattern of methods / functions - (2011-08-12)
  [3509] Operator Overloading, Exceptions, Pointers, References and Templates in C++ - new examples from our courses - (2011-11-06)
  [3982] Using a vector within an object - C++ - (2013-01-19)

C235 - C and C based languages - I/O in C++
  [1675] Comparing Objects in C++ - (2008-06-13)
  [3124] C++ - putting the language elements together into a program - (2011-01-08)
  [3390] Printing objects in C++ - (2011-08-13)
  [3807] Reading (and writing) files in C++ - (2012-07-18)
  [4562] Left shift operator on an output stream object - C++ - (2015-10-30)
  [4563] Formatting and outputting your own classes in C++ - (2015-10-30)

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Is this number between? Does this list include? - Ruby
C++ - unknown array size, unknown object type. Help!
C++ - objects that are based on other objects, saving coding and adding robustness
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Events - Spring and Early Summer 2011 in Melksham
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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