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Input/Output of Objects

Input Output of Objects

This chapter and Chapter 15 introduced C++'s object-oriented style of input/output. However, our examples concentrated on I/O of traditional data types rather than objects of user-defined types. In Chapter 11, we showed how to input and output objects using operator overloading. We accomplished object input by overloading the stream extraction operator >> for the appropriate istream. We accomplished object output by overloading the stream insertion operator << for the appropriate ostream. In both cases, only an object's data members were input or output, and, in each case, they were in a format meaningful only for objects of that particular abstract data type. An object's member functions are not input and output with the object's data; rather, one copy of the class's member functions remains available internally and is shared by all objects of the class.

When object data members are output to a disk file, we lose the object's type information. We store only data bytes, not type information, on the disk. If the program that reads this data knows the object type to which the data corresponds, the program will read the data into objects of that type.

An interesting problem occurs when we store objects of different types in the same file. How can we distinguish them (or their collections of data members) as we read them into a program? The problem is that objects typically do not have type fields (we studied this issue carefully in Chapter 13).

One approach would be to have each overloaded output operator output a type code preceding each collection of data members that represents one object. Then object input would always begin by reading the type-code field and using a switch statement to invoke the proper overloaded function. Although this solution lacks the elegance of polymorphic programming, it provides a workable mechanism for retaining objects in files and retrieving them as needed.

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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