tYSR20

222Part III: Introduction to ClassesJustifying constructorsSomething as straightforward as adding arguments to the constructorshouldn’t require much justification, but let me take a shot at it anyway. First,allowing arguments to constructors is convenient. It’s a bit silly to make programmersconstruct a default object and then immediately call an initializationfunction to store data in it. A constructor with arguments is like one-stopshopping — sort of a full-service constructor.Another more important reason to provide arguments to constructors is thatit may not be possible to construct a reasonable default object. Rememberthat a constructor’s job is to construct a legal object (legal as defined by theclass). If some default object is not legal, the constructor isn’t doing its job.For example, a bank account without an account number is probably not legal.(C++ doesn’t care one way or the other, but the bank might get snippy.) Youcould construct a numberless BankAccount object and then require that theapplication use some other member function to initialize the account numberbefore it’s used. This “create now/initialize later” approach breaks the rules,however, because it forces the class to rely on the application for initialization.Using a constructorConceptually, the idea of adding an argument is simple. A constructor is amember function, and member functions can have arguments. Therefore,constructors can have arguments.Remember, though, that you don’t call the constructor like a normal function.Therefore, the only time to pass arguments to the constructor is when theobject is created. For example, the following program creates an object s ofthe class Student by calling the Student(char*) constructor. The object sis destructed when the function main() returns.//// ConstructorWArg - provide a constructor with arguments//#include #include #include using namespace std;const int MAXNAMESIZE = 40;class Student{public:Student(char* pName){strncpy(name, pName, MAXNAMESIZE);name[MAXNAMESIZE - 1] = ‘\0’;