Operator overloading

• C++ lets you create new types but not new operators. However, you can overload existing operators, i.e. define their behavior of used with the newly defined types. You must overload operators to use them on class objects. Only the assignment (=) and address (&) operators can be used with every class without explicit overloading.

• Some operators are already overloaded in C++. For example: +, - which work with int, floats etc...

• Use operator overloading when it makes a program clearer, don't overload operators in a way that makes the program difficult to understand. For example, it is possible to overload + to substract and overload / to multiply, but it is extremely bad style. (Note: you can't change the way C++ operators work with built-in types, for example the addition of two integers)

• What operators can you overload? Look at figure 8.1 in D&D for a list. If you try to overload an operator that can't be overloaded or to create a new operator via overloading, you will get a syntax error.

• Should the overloaded operator be a member function? a friend?
  • member function: if it needs to access the private data members of the class and the leftmost operand is a class object
    Ex: newtype operator+ (newtype, newtype)
  • friend function: can't satisfy the condition for a member function, but still needs to access the private data members Ex: ostream& operator<< (ostream&, classname&)
    istream& operator>> (istream&, classname&)
  • none of the above if it does not need to access the private data members directly (it still can through accessor functions)

Building a class for a student

Suppose that you were to build a class for a school to store information regarding students. You want to keep track of certain information regarding each student who is enrolled at the school, and you want to provide functions that will enable the school to store/retrieve information regarding a given student.

Data to keep track of:

• name (string)
• date of birth (as a string day/month/year)
• id number (an int)
• gpa (float)
• major (enum)

Functions to build:
Of course, there should be constructors (at least one), amd accessor methods (functions to get the value of the private data members or to set those values). There is a function that computes and returns the age of the person, and one that overloads the << operator to print all the information regarding the student.

Of course, there are many many many other things you could do... Feel free to add them!

The following files contain the code:
student.h : contains the class
student.cc : contains the definitions for the public member functions and friend functions of the class
studentmain.cc : a sample main

To compile this program, just type: g++ student.cc studentmain.cc -o student

Building a vector class

Build a class to hold 2-dimensional vectors.

What do you need?

• private data members to hold the x and y coordinates of the vector
• constructors, a destructor
• accessor functions (getcoordinates, setcoordinates)
• overload operators (+, -, <<...)

vector.h
vector.cc
vectormain.cc

To compile this, type
g++ vector.cc vectormain.cc -o vector