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Overloading Unary Operators

A unary operator for a class can be overloaded as a non-static member function with no arguments or as a global function with one argument; that argument must be either an object of the class or a reference to an object of the class. Member functions that implement overloaded operators must be non-static so that they can access the non-static data in each object of the class. Remember that static member functions can access only static data members of the class.

Later in this chapter, we will overload unary operator ! to test whether an object of the String class we create (Section 11.10) is empty and return a bool result. Consider the expression !s, in which s is an object of class String. When a unary operator such as ! is overloaded as a member function with no arguments and the compiler sees the expression !s, the compiler generates the call s.operator!(). The operand s is the class object for which the String class member function operator! is being invoked. The function is declared in the class definition as follows:

 class String
 {
 public:
 bool operator!() const;
 ...
 }; // end class String

A unary operator such as ! may be overloaded as a global function with one argument in two different wayseither with an argument that is an object (this requires a copy of the object, so the side effects of the function are not applied to the original object), or with an argument that is a reference to an object (no copy of the original object is made, so all side effects of this function are applied to the original object). If s is a String class object (or a reference to a String class object), then !s is treated as if the call operator!( s ) had been written, invoking the global operator! function that is declared as follows:

 bool operator!( const String & );


Introduction to Computers, the Internet and World Wide Web

Introduction to C++ Programming

Introduction to Classes and Objects

Control Statements: Part 1

Control Statements: Part 2

Functions and an Introduction to Recursion

Arrays and Vectors

Pointers and Pointer-Based Strings

Classes: A Deeper Look, Part 1

Classes: A Deeper Look, Part 2

Operator Overloading; String and Array Objects

Object-Oriented Programming: Inheritance

Object-Oriented Programming: Polymorphism

Templates

Stream Input/Output

Exception Handling

File Processing

Class string and String Stream Processing

Web Programming

Searching and Sorting

Data Structures

Bits, Characters, C-Strings and structs

Standard Template Library (STL)

Other Topics

Appendix A. Operator Precedence and Associativity Chart

Appendix B. ASCII Character Set

Appendix C. Fundamental Types

Appendix D. Number Systems

Appendix E. C Legacy Code Topics

Appendix F. Preprocessor

Appendix G. ATM Case Study Code

Appendix H. UML 2: Additional Diagram Types

Appendix I. C++ Internet and Web Resources

Appendix J. Introduction to XHTML

Appendix K. XHTML Special Characters

Appendix L. Using the Visual Studio .NET Debugger

Appendix M. Using the GNU C++ Debugger

Bibliography

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C++ How to Program
C++ How to Program (5th Edition)
ISBN: 0131857576
EAN: 2147483647
Year: 2004
Pages: 627
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