C++ functions can be declared to use default values when none are supplied Class Circle { Float xc, yc, radius; Circle(float x, float y, float r=1.0); … } Example usage: Circle c1(1.0, 1.0); // omit def param; use 1.0 Circle c2(1.0, 1.0, 2.0); // supply “custom” value CS-1030 Dr. Mark L. Hornick

Review: C++ parameter passing Passing entire objects by value in C++ is not always desirable Objects can be big, leading to inefficiency Copy constructor must be called to make the copy of the object… Passing by reference or by address eliminates the need to copy entire objects Only the 4-byte address is copied Java only passes object references CS-1030 Dr. Mark L. Hornick

Review: parameter passing by object, reference, and address Review: Here’s a declaration of a method that passes an object by value: void printName(Employee e); Usage: printName( anEmp ); Here’s the modified declaration of the method to tell it to pass the object by reference instead: void printName(Employee& e); Usage: printName( anEmp ); // same as above Here’s the modified declaration of the method to tell it to pass the object by address instead: void printName(Employee* pe); Usage: printName( &anEmp ); // address of object CS-1030 Dr. Mark L. Hornick

Passing by reference or address – always advantageous? Useful if you want a method to be able to modify the variable you are passing to the method But what if you want to prevent a method from modifying the variable? CS-1030 Dr. Mark L. Hornick

The const specifier Prevents objects passed by reference or address from being changed within a method Here’s the modified declaration of the method that passes by reference: void printName(const Employee& e); Usage: printName( anEmp ); Here’s the modified declaration of the method that passes by address: void printName(const Employee* pe); Usage: printName( &anEmp ); CS-1030 Dr. Mark L. Hornick

Notation for const and pointers is tricky int x; const int* ptr1 = &x; // Can’t use ptr1 to change x, but can change ptr1 to point to another object int* const ptr2 = &x; // Can’t change ptr2 to another object, but can change value of x const int* const ptr2 = &x; // Can’t do either CS-1030 Dr. Mark L. Hornick

const data objects within classes class Employee { const int ID; Employee(); // def constructor Employee(int id); // constructor … } Constructor is still called, but const data cannot be initialized in the constructor So how do you set it? CS-1030 Dr. Mark L. Hornick

const data objects within classes - Initializers class Employee { const int ID; Employee():ID=0; Employee(int id):ID(id); … } Initializer Data members are initialized before the constructor is actually invoked CS-1030 Dr. Mark L. Hornick

const Member Functions May not alter data members of the class May not call other member functions that modify data members of the class Example CS-1030 Dr. Mark L. Hornick

static Data Members Same concept as Java’s static Belong to all objects of the same type (class) Shared by all instances Don’t need an object to exist Must be defined outside the class But declared inside Example CS-1030 Dr. Mark L. Hornick

static Member Functions Belong to the class Not the object! Don’t require an object to be used May only access static data members Example CS-1030 Dr. Mark L. Hornick

Who can you trust? Private members have limited scope …only methods in the same class can access them This can be circumvented any function (from any other class) can be given access to a private data member or method The outside function must be declared as a friend must be part of the class definition CS-1030 Dr. Mark L. Hornick

Friends An entire class can be made a friend of another class The class must be declared as a friend The declaration must be part of the class definition Friendship is not mutual If class A declares class B as a friend, the friendship is not automatically reciprocated Class B would have to declare class A as a friend CS-1030 Dr. Mark L. Hornick