Function and Operator Overloading

Overloading Review of function overloading –It is giving several definitions to a single function name –The compiler can figure out which definition to use by the number and type of arguments Operator overloading is giving additional definitions to operators Some operators that can be overloaded +, -, >, <, [ ], *, etc

The difference between a function and an operator An operator (such as +) is really just a function with different syntax In a function, the argument are placed in parentheses after the function name, as in: –add(cost, tax) –This is postfix notation For an operator, the argument are placed on either side of the operator, as in: –cost + tax –This is infix notation

Advantages of operator overloading The point of operator overloading is to provide the same concise expression for user-defined types as built in types It is just clearer and simpler to say –Cost + tax, than to say –Add(cost, tax)

The role of types in overloading C++ programming is a type sensitive and type- focused process Programmers can use built-in types or define their own types Operators can be used with user-defined types as well as built-in types –The operators new meaning must be defined The compiler uses the type of the arguments to decide which definition to use for overloaded functions or operators

How operators are overloading You write a function (with a header and body) as you normally would The function name is now the keyword operator followed by the symbol to be overloaded –Example: return_type operator++( ) To use an operator on a class object, that operator must be overloaded (with a couple of exceptions) –The assignment operator (=) –The address operator (&)

Restrictions on operator overloading The precedence of an operator cannot be changed by overloading. –An aside on precedence—table on precedence You cannot change the number of operands(arguments) an operators takes –Unary operators remain unary; binary remain binary; the only ternary operator (:?) cannot be overloaded It is not possible to create new operators –So ** for exponentiation cannot be created

Operator functions as class members vs. as friend functions They can be either class members or friends As member functions: –The leftmost (or only) argument must be a class object or reference to a class object If the left operand must be a built-in type or object of a different class, it must be a non- member function –If it must access private members of the class directly, then it must be a friend function

Data Conversions Type conversions between built-in data types may be implicit or explicit –Use static_cast (old_type_variable) for explicit type conversions All conversions between objects and built-in types must be explicit Example: convert 5 feet 3 inches to 5.25 feet this is a conversion from Distance to a float