Page 146 - DCAP404 _Object Oriented Programming

Unit 7: Operator Overloading

will not evaluate all three operations and will stop after a false one is found. This behavior does Notes
not apply to operators that are overloaded by the programmer.
Even the simplest C++ application, like a “hello world” program, is using overloaded operators.
This is due to the use of this technique almost everywhere in the standard library (STL). Actually
the most basic operations in C++ are done with overloaded operators, the IO(input/output)
operators are overloaded versions of shift operators(<<, >>). Their use comes naturally to many
beginning programmers, but their implementation is not straightforward. However a general
format for overloading the input/output operators must be known by any C++ developer. We
will apply this general form to manage the input/output for our Complex class:

friend ostream &operator<<(ostream &out, Complex c) //output
{
out<<“real part: “<<real<<“\n”;
out<<“imag part: “<<imag<<“\n”;
return out;

}
friend istream &operator>>(istream &in, Complex &c) //input
{
cout<<“enter real part:\n”;
in>>c.real;
cout<<“enter imag part: \n”;
in>>c.imag;
return in;

}

Notes Note that the use of the friend keyword in order to access the private members in
the above implementations. The main distinction between them is that the operator>>
may encounter unexpected errors for incorrect input, which will make it fail sometimes
because we haven’t handled the errors correctly.
A important trick that can be seen in this general way of overloading IO is the returning
reference for istream/ostream which is needed in order to use them in a recursive manner:
Complex a(2,3);
Complex b(5.3,6);
cout<<a<<b;

Self Assessment

Fill in the blanks:

1. The ……………………….. operator works by giving the value of one variable to another
variable of the same type or closely similar.
2. Operators are overloaded in C++ by creating operator functions either as a member or as
a ……………………….. of a class.

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