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<META NAME="Author" CONTENT="James M. Rogers">
<META NAME="Description" CONTENT="This article is the sixth in a series designed to explore the Standard C library implementation available for Linux">
<META NAME="Keywords" CONTENT="linux, standard c library, character functions">
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<TITLE>The Standard C Library for Linux Issue 41</TITLE>
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<H4>
"Linux Gazette...<I>making Linux just a little more fun!</I>"
</H4>
<P> <HR> <P>
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<CENTER>
<H1>
<FONT COLOR="#800000">The Standard C Library for Linux</FONT></H1></CENTER>
<CENTER>
<H3>
<FONT COLOR="#000080">Part Six: <assert.h> Diagnostics for Programmers</FONT></H3></CENTER>
<CENTER>
<H4>
By <A HREF="mailto:jrogers@u.washington.edu">James M. Rogers</A></H4></CENTER>
<HR>
<P>The last article was on <stdlib.h> Standard Library. This article
is on <assert.h> Diagnostics for Programmers.
<P>I am assuming a knowledge of c programming on the part of the reader.
There is no guarantee of accuracy in any of this information nor suitability
for any purpose.
<P>If used properly assertions will allow programmers to much more easily
document and debug your code with no impact on runtime performance.
Assertions are not meant to be used for production code as they cause the
program to terminate with an error condition. Since assertions are
never to be used in production code they are not useful in finding runtime
errors such as a failure to allocate memory. You must still handle
failed return conditions of all function calls the same as always.
<P>Instead, what assertions allow you to do is document the assumptions
that you make as you program and allow you to debug the obvious logic errors
that you have made. As you program around these logic errors you
can modify your assertions to not die on errors that you are now handling.
<P>The example is <A HREF="rogers_example06.c">rogers_example06.c</A>
. In this program I will demonstrate the use of assertions by using
a simple program that asks for two numbers and then divides the first number
by the second. Compile the program with the following:
<P>gcc -DNDEBUG rogers_example06.c -o assert
<P>and then run ./assert and try to divide by zero. The flag -NDEBUG will
cause your assertion to generate no runtime code. This flag should
be used in all production environements
<P>Your program will core dump with almost no indication of the problem.
Now recompile the program with the following:
<P>gcc rogers_example06.c -o assert
<P>Now run the program again and again try to divide by zero. This
time it should be much more apparrent what the problem is and very easy
to locate the exact line that had the problem.
<P>As always, if you see an error in my documentation please tell me and
I will correct myself in a later document. See corrections at end
of the document to review corrections to the previous articles.
<P><B><FONT SIZE=+1>Assertions</FONT></B>
<UL><TT>#include <assert.h></TT>
<P><TT>void assert(int expression);</TT></UL>
<P>
<HR>
<P>A correction to Part *:
<BR>
<P>
<HR>
<H4>
Bibilography:</H4>
<I>The ANSI C Programming Language, Second Edition</I>, Brian W. Kernighan,
Dennis M. Ritchie, Printice Hall Software Series, 1988
<P><I>The Standard C Library</I>, P. J. Plauger, Printice Hall P T R, 1992
<P><I>The Standard C Library, Parts 1, 2, and 3</I>, Chuck Allison, <I>C/C++
Users Journal</I>, January, February, March 1995
<P>STDIO(3), BSD MANPAGE, <I>Linux Programmer's Manual</I>, 29 November
1993
<P> <HR><P>
<BR>
<CENTER>
<H4>
Previous "The Standard C Library for Linux" Articles</H4></CENTER>
<A HREF="http://www.linuxgazette.com/issue24/rogers.html"><I>The Standard
C Library for Linux, stdio.h</I>, James M. Rogers, January 1998</A>
<BR><A HREF="http://www.linuxgazette.com/issue31/rogers1.html"><I>The Standard
C Library for Linux, stdio.h</I>, James M. Rogers, July 1998</A>
<BR><A HREF="http://www.linuxgazette.com/issue32/rogers.html"><I>The Standard
C Library for Linux, stdio.h</I>, James M. Rogers, August 1998</A>
<BR><A HREF="http://www.linuxgazette.com/issue38/rogers.html"><I>The Standard
C Library for Linux, ctype.h</I>, James M. Rogers, March 1999</A>
<BR><A HREF="http://www.linuxgazette.com/issue39/rogers.html"><I>The Standard
C Library for Linux, stdlib.h</I>, James M. Rogers, April 1999</A>
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<center><H5>Copyright © 1999, James M. Rogers <BR>
Published in Issue 41 of <i>Linux Gazette</i>, May 1999</H5></center>
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