Constructors, Destructors and Exception Handling

First, let us discuss an issue that we have mentioned but not yet resolved satisfactorily: What happens when an error is detected in a constructor? For example, how should an object's constructor respond when new fails because it was unable to allocate required memory for storing that object's internal representation? Because the constructor cannot return a value to indicate an error, we must choose an alternative means of indicating that the object has not been constructed properly. One scheme is to return the improperly constructed object and hope that anyone using it would make appropriate tests to determine that it is in an inconsistent state. Another scheme is to set some variable outside the constructor. Perhaps the best alternative is to require the constructor to tHRow an exception that contains the error information, thus offering an opportunity for the program to handle the failure.

Exceptions thrown by a constructor cause destructors to be called for any objects built as part of the object being constructed before the exception is thrown. Destructors are called for every automatic object constructed in a try block before an exception is thrown. Stack unwinding is guaranteed to have been completed at the point that an exception handler begins executing. If a destructor invoked as a result of stack unwinding throws an exception, terminate is called.

If an object has member objects, and if an exception is thrown before the outer object is fully constructed, then destructors will be executed for the member objects that have been constructed prior to the occurrence of the exception. If an array of objects has been partially constructed when an exception occurs, only the destructors for the constructed objects in the array will be called.

An exception could preclude the operation of code that would normally release a resource, thus causing a resource leak. One technique to resolve this problem is to initialize a local object to acquire the resource. When an exception occurs, the destructor for that object will be invoked and can free the resource.

Error-Prevention Tip 16.4

When an exception is thrown from the constructor for an object that is created in a new expression, the dynamically allocated memory for that object is released.

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


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


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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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