preface.html.svn-base

纯C数据结构

projects off the ground. This usage helps students realize the enormous savings
that reuse can bring to a project, and it often induces them to try
interface-based design for their own parts of the project. This latter effect is
particularly valuable in team projects, because that's a way of life in the "real
world.&quot;</P>
<P>Interfaces and implementations are the focus of Princeton's sophomore-level
systems programming course. Assignments require students to be interface
clients, implementors, and designers. In one assignment, for example, I
distribute Section 8.1's <CODE>Table</CODE> interface, the object code for its
implementation, and the specifications for Section 8.2's word frequency program,
<CODE>wf</CODE>. The students must implement <CODE>wf</CODE> using only my
object code for <CODE>Table</CODE>. In the next assignment, they get the object
code for <CODE>wf</CODE>, and they must implement <CODE>Table</CODE>.
Sometimes, I reverse these assignments, but both orders are eye-openers for most
students. They are unaccustomed to having only object code for major parts of
their program, and these assignments are usually their first exposure to the
semiformal notation used in interfaces and program specification.</P>
<P>Initial assignments also introduce checked runtime errors and assertions as
integral parts of interface specifications. Again, it takes a few assignments
before students begin to appreciate the value of these concepts. I forbid &quot;unannounced&quot;
crashes; that is, crashes that are not announced by an assertion failure
diagnostic. Programs that crash get a grade of zero. This penalty may seem
unduly harsh, but it gets the students' attention. They also gain an
appreciation of the advantages of safe languages, like ML and Modula-3, in which
unannounced crashes are impossible. <SMALL>(This grading policy is less harsh
than it sounds, because in multipart assignments, only the offending part is
penalized, and different assignments have different weights. I've given many
zeros, but none has ever caused a course grade to shift by a whole point.)</SMALL></P>
<P>Once students have a few interfaces under their belts, later assignments ask
them to design new interfaces and to live with their design choices. For
example, one of <A HREF="http://www.cs.princeton.edu/~appel/">Andrew Appel</A>'s
favorite assignments is a primality testing program. Students work in groups to
design the interfaces for the arbitrary-precision arithmetic that is needed for
this assignment. The results are similar to the interfaces described in Chapters
17 through 19. Different groups design interfaces, and a postassignment
comparison of these interfaces, in which the groups critique on one anothers'
work, is always quite revealing. <A HREF="http://www.cs.princeton.edu/~li/">Kai
Li</A> accomplishes similar goals with a semester-long project that builds an
X-based editor using the <A HREF="http://www.sunlabs.com/research/tcl/">Tcl/Tk
system</A> (J.K. Ousterhout, <CITE>Tcl and the Tk Toolkit</CITE>,
Addison-Wesley, 1994) and editor-specific interfaces designed and implemented by
the students. Tk itself provides another good example of interface-based design.</P>
<P>In advanced courses, I usually package assignments as interfaces and give
the students free rein to revise and improve on them, and even to change the
goals of the assignment. Giving them a starting point reduces the time required
for assignment, and allowing substantial changes encourages creative students to
explore alternatives. The unsuccessful alternatives are often more educational
than the successful ones. Students invariably go down the wrong road, and they
pay for it with greatly increased development time. When, in hindsight, they
understand their mistakes, they come to appreciate that designing good
interfaces is hard, but worth the effort, and they almost always become converts
to interface-based design.</P>
<H2>How to Get the Software</H2>
<P>The software in this book has been tested on the following platforms.</P>
<BLOCKQUOTE>
<TABLE CELLPADDING="12">
<TR ALIGN="LEFT" VALIGN="TOP">
<TH><I>Processor</I></TH>
<TH><I>Operating Systems</I></TH>
<TH><I>Compilers</I></TH></TR>
<TR ALIGN="LEFT" VALIGN="TOP">
<TD ALIGN="LEFT">SPARC</TD>
<TD>SunOS 4.1</TD>
<TD>lcc 3.5<BR>gcc 2.7.2</TD></TR>
<TR ALIGN="LEFT" VALIGN="TOP">
<TD>Alpha</TD>
<TD>OSF/1 3.2A</TD>
<TD>lcc 4.0<BR>gcc 2.6.3<BR>cc</TD></TR>
<TR ALIGN="LEFT" VALIGN="TOP">
<TD>MIPS R3000</TD>
<TD>IRIX 5.3</TD>
<TD>lcc 3.5<BR>gcc 2.6.3<BR>cc</TD></TR>
<TR ALIGN="LEFT" VALIGN="TOP">
<TD>MIPS R3000</TD>
<TD>Ultrix 4.3</TD>
<TD>lcc 3.5<BR>gcc 2.5.7</TD></TR>
<TR ALIGN="LEFT" VALIGN="TOP">
<TD>Pentium</TD>
<TD>Windows 95<BR>Windows NT 3.51<BR><SMALL>(except for Threads)</SMALL></TD>
<TD>Microsoft Visual C/C++ 4.0</TD></TR></TABLE></BLOCKQUOTE>
<P>A few of the implementations are machine-specific; they assume that the
machine has two's-complement integer and IEEE floating-point arithmetic, and
that unsigned longs can hold object pointers.</P>
<P>The source code for everything in this book is available for
<A HREF="ftp://ftp.cs.princeton.edu/pub/packages/cii">anonymous ftp</A> at
<TT>ftp.cs.princeton.edu</TT> in <TT>pub/packages/cii</TT>. Use an <TT>ftp</TT>
client to connect to <TT>ftp.cs.princeton.edu</TT>, change to the directory
<TT>pub/packages/cii</TT>, and download the file
<A HREF="ftp://ftp.cs.princeton.edu/pub/packages/cii/README">README</A>, which
describes the contents of the directory and how to download the distribution.</P>
<P>The most recent distributions are usually in files named <TT>cii</TT><I>xy</I><TT>.tar.gz</TT>
or <TT>cii</TT><I>xy</I><TT>.zip</TT>. <I>xy</I> is the version number,
e.g., 10 is version 1.0. <TT>cii</TT><I>xy</I><TT>.tar.gz</TT> is a U<SMALL>NIX</SMALL>
tar file compressed with <TT>gzip</TT>, and <TT>cii</TT><I>xy</I><TT>.zip</TT>
is a ZIP file compatible with PKZIP version 2.04g. The files in
<TT>cii</TT><I>xy</I><TT>.zip</TT> are DOS/Windows text files; that is, their
lines end with carriage returns and linefeeds.
<TT>cii</TT><I>xy</I><TT>.zip</TT> may also be available on America Online,
Compuserve, and other online services.</P>
<P>Information is also available on the World-Wide Web at URL
<A HREF="http://www.cs.princeton.edu/software/cii/">http://www.cs.princeton.edu/software/cii/</A>.
This page includes instructions on reporting bugs.</P>
<H2>Acknowledgments</H2>
<P>I have been using some of the interfaces in this book for my own research
project and in courses at the University of Arizona and Princeton University
since the late 1970s. Students in these courses have been guinea pigs for my
drafts of these interfaces. Their feedback over the years has been an important
contribution to both the code in this book and its explanation. The Princeton
students in several offerings of COS 217 and COS 596 deserve special thanks,
because they suffered unknowingly through the drafts of most of what's in this
book.</P>
<P>Interfaces are a way of life at Digital's System Research Center (SRC), and
my 1992 and 1993 summers at SRC working on the Modula-3 project erased any
doubts I may have harbored about the efficacy of this approach. My thanks to SRC
for supporting my visits, and to Bill Kalsow, Eric Muller, and Greg Nelson for
many illuminating discussions.</P>
<P>My thanks to IDA's Centers for Communications Research in Princeton and La
Jolla for their support during the summer of 1994 and during my 1995&#150;96
sabbatical. The CCRs provided ideal hideouts at which to plan and complete this
book.</P>
<P>Technical interactions with colleagues and students have contributed to this
book in many ways. Even seemingly unrelated discussions have provoked
improvements in my code and in its explanation.  Thanks to Andrew Appel, Greg
Astfalk, Jack Davidson, John Ellis, Mary Fern&aacute;ndez, Chris Fraser, Alex
Gounares, Kai Li, Jacob Navia, Maylee Noah, Rob Pike, Bill Plauger, John Reppy,
Anne Rogers, and Richard Stevens. Careful readings of my code and prose by Rex
Jaeschke, Brian Kernighan, Taj Khattra, Richard O'Keefe, Norman Ramsey, and
David Spuler made a significant contribution to the quality of both.</P>
<P><A HREF="./">Back to the CII home page</A>.</P>
<HR>
<ADDRESS><A HREF="http://www.cs.princeton.edu/~drh/">David Hanson</A> /
<A HREF="mailto:[e-mail]">[e-mail]</A><BR>$Revision: 1.8 $ $Date$
</ADDRESS></BODY></HTML>