C++ Programming for Graphics Lecture 5 References, New, Arrays and Destructors

Introduction References New Arrays –by type –by pointers Destructors

Constructors - Extra If the class does not contain a constructor –The system provides a default If the class contains one or more –You lose the default constructor. –You have to provide all required.

References Referring back to the “swap” function Instead of passing values. Passed addresses of the variables when calling function. Manipulated values by dereferencing. Had to remember to use “&” and “*”

References C++ has “reference type” Do not need to use “&” and “*” when using. Declared by –basic type, followed by –“&” –e.g int&“reference to an integer” double&“reference to a double”

Reference Usage Must declare and initialise at same time E.g. –intnCount; –int&refInt = nCount; Can then access the value by –using “nCount” –or its alias –refInt

References and classes Can use references for classes E.g.Account Freddy; Account& refAcc = Freddy; so, can access the object using either E.gFreddy.setBalance(13.26); refAcc.setBalance(13.26); Both – produce the same result.

New So far – instantiated by “name” –e.g. Account Freddy; Account Tripta(12.36, 2.5, 2); Can also use “new” –similar to malloc() –much easier to use. –allocates memory for the object. –returns a pointer to the memory address.

Using “new” First need a pointer –e.g. Account *pAcc; Now instantiate –e.g. pAcc = new Account; or with arguments –pAcc = new Account(12.36, 2.4, 6);

Error trapping If “new” is unable to acquire memory –it will return “NULL” Should always test for this –e.g. Account *pAcc = new Account(12.36, 2.4, 1); if(!pAcc)// test for NULL { // Error handler cout << “Error allocating memory”; exit(1);// terminate application }

Accessing the object When using a pointer. Methods etc. are accessed differently Using “.” notation –e.g.(*pAcc).setBalance(15.26); Using an alternative notation “ -> ” –e.g.pAcc->setBalance(15.26);

Arrays So far, have used names for our accounts. Have just seen how to use individual pointers. Not very efficient! We can do better than that …. –Array of class objects. –Array of pointers. –Linked lists- later lecture

Array Indexing Don’t forget……. –If you declare an array e.g.arAccs[10] –The indexing values are 0 to 9 –NOT1 to 10 Also – don’t forget that in C/C++ there is no bounds checking.

Array example Declaration –Account arAccs[3]; This will work only under certain conditions –The class does not have a constructor or –The class has a constructor that does not require arguments.

Arrays and Constructor Args Account arAcc[3]; If Account has constructors that require zero arguments – equivalent to… Account arAcc[3] = {account(), account(), account()};

Arrays and Constructor Args If wanted to include arguments. Account arAccs[3] = {account(12.36, 1.2, 1), account(100.52, 2.5, 2), account(125.0, 2.5, 3)}; There are many other possibilities, all dependant upon the number of arguments required. You should consult your text books etc. for more information regarding this matter.

Arrays and Pointers Also possible to have an array of pointers. –e.g. Account *parAccs[10]; An array of pointers to objects of type account Instantiation –e.g. parAccs[0] = new Account(12.36, 2.5, 1);

Multiple Instantiations Account *parAccs[10]; // Instantiate a number of Accounts for(int nCount = 0; nCount < 10; nCount++) { parAccs[nCount] = new Account(0.0, 0.0, nCount +1); } // Access a single account cout getBalance() << endl << endl;

Destructors Just as a class can have constructors –That are “special” methods which….. –are called when instantiating an object It can also have a “special” methods that are called when deleting an object –These are called “destructors” –Take the same name as the class –But preceded by the “tilde” character – “~”

Destructors So, for the class – Account. The destructor would be…. – ~Account Destructors –Do not return a value. –Do not accept any arguments. –Called automatically when using “delete”. –Maximum of one per class.

“delete” Just as “new” will acquire memory “delete” will release it back to the system Can only be used when memory via “new” –See malloc() & free (‘C’ programming) Use of delete –“Tidy up” objects – esp. if holding pointers. –Save object data. –etc.

Summary In this lecture have considered –References –Use of “new” –Arrays - by type - by pointers –“new” –Destructors –“delete”

Next Lecture Copy Constructors Overloading operators –This is challenging so make sure you are up to date with the work.