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纯C数据结构

some of the grunt programming needed to get such 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
&quot;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 projects 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醤dez, 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>

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<address>
  <a HREF="http://www.research.microsoft.com/~drh/">David Hanson</a> / <a
  HREF="mailto:[e-mail]">[e-mail]</a><br>
  $Revision: 1.13 $ $Date$ 
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