F.9. Assertions

The assert macrodefined in the header filetests the value of an expression. If the value of the expression is 0 (false), then assert prints an error message and calls function abort (of the general utilities library) to terminate program execution. This is a useful debugging tool for testing whether a variable has a correct value. For example, suppose variable x should never be larger than 10 in a program. An assertion may be used to test the value of x and print an error message if the value of x is incorrect. The statement would be

assert( x <= 10 );

If x is greater than 10 when the preceding statement is encountered in a program, an error message containing the line number and file name is printed, and the program terminates. The programmer may then concentrate on this area of the code to find the error. If the symbolic constant NDEBUG is defined, subsequent assertions will be ignored. Thus, when assertions are no longer needed (i.e., when debugging is complete), we insert the line

#define NDEBUG

in the program file rather than deleting each assertion manually. As with the DEBUG symbolic constant, NDEBUG is often set by compiler command-line options or through a setting in the IDE.

Most C++ compilers now include exception handling. C++ programmers prefer using exceptions rather than assertions. But assertions are still valuable for C++ programmers who work with C legacy code.

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


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

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