1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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