If you declare a variable to be of an object type in C++ (and potentially do so with parameters), you're going to be assigning memory for the variables that it includes on the stack - i.e. within memory that will be lost when you exit the closure (block of code - function - method) in which you are defining it.

BUT if you declare a pointer to a variable of a certain type, and then fill the variable with data using the new keyword, then only the pointer to that object is in local space on the stack, and the data itself will be on the heap. This means that if you return the pointer, or copy it into a more permanent piece of storage, you will retain the data that it contains even when the original closure has been completed.

In other words, you really want to construct your objects via new most of the time, the exception being where you have an object that's only going to have a very local and limited lifetime.

The notation for accessing a method within an object uses a dot - for example:
  savoy.setoccu(0.43);
and if you extend that to reference a method within an object for whcih you hold a pointer, you get the somewhat ugly form:
  (*ritz).setoccu(0.76);
You're provided with "syntactic icing" in C++ to make this prettier using the -> operator instead, thus:
  ritz->setoccu(0.76);

There's in example that sets up a hotel called "savoy" to hold data about a hotel, and a pointer to a hotel called "ritz" pointing to data on the heap [here]; you can find the source code of the class it uses [here] and the header file included in both [here].
(written 2010-01-16)

 C232 - C and C based languages - Defining and using classes in C++
  [1925] Introduction to Object Oriented Programming - (2008-12-06)
  [2577] Complete teaching example - C++, inheritance, polymorphism - (2010-01-15)
  [2579] Creating, setting up and using objects in C++ - (2010-01-16)
  [3250] C++ - how we teach the language and the concepts behind the language - (2011-04-17)
  [3716] Learning C++ - a design pattern for your first class - (2012-05-02)
  [3721] Naming blocks of code, structures and Object Orientation - efficient coding in manageable chunks - (2012-05-06)
  [3810] Reading files, and using factories to create vectors of objects from the data in C++ - (2012-07-21)
  [3978] Teaching OO - how to avoid lots of window switching early on - (2013-01-17)
  [4129] Simple OO demonstration in C++, comparison to Python - (2013-07-01)
  [4372] Template / design pattern for C++ constructor and accessors - (2014-12-29)
  [4565] Allocation of memory for objects in C++ - Stack v Heap - (2015-10-31)

Back to Complete teaching example - C++, inheritance, polymorphism

Previous and next or Horse's mouth home

Forward to Creating, setting up and using objects in C++

Starting to arrange the picture library
Snow scenes - and how snow effected our business
C course inspires new teaching examples
Where are your objects stored in C++?
What does const mean? C and C++
Sharing variables between files of code in C - extern
Summary of Wiltshire Core Strategy responses
C Structs - what, how and why