cnews018.doc

经过改进的C语言位操作功能

      Issue                        C News                             2


      ================================================================= 
      THE HEAP by Barry Lynch    
      ================================================================= 



           The postcards keep coming and we truly appreciate the
      support that has been shown over the last two years.  This issue
      of C News marks the end of Volume 1 of C News.  And beginning
      with Issue 19, we will start Volume 2 with a few new twists.
      (Can't say what they are yet, still working out the details...) 

           This issue contains another installment of Wayne
      Dernoncourt's Beginner's Column.  This month Wayne starts
      exploring the wondrous world(???) of sort algorithms.  Wayne's
      article started as a result of a C News staff meeting we had at
      a local pizzeria a few months ago.  Matter of fact, quite a few
      things had their start that night at the pizzeria.  

           Roy Browning took the time to sit down and write a few
      words on his explorations into C++.  While I can't claim Roy as
      the official C News "C++" guru, we can look forward to his
      thoughts as he discovers more about C++.  Welcome aboard Roy! 

           Paul Castle sent us an article on command line parsing
      which does a nice job of explaining the concepts of command line
      parsing to beginner C programmers.  

           Jim Singleton - who is beginning to take over C News (grin)
      - starts a series on software development in this issue.  If you
      recall, from a previous issue of C News, Jim and I started
      developing an Opus utility to measure my BBS system usage.
      Alas, Dan Kozak decided to show off and wrote an AWK script to
      accomplish the same thing.  Before Jim and I could get started,
      Dan was already over the finish line.  Well after that
      embarrassing episode, Jim threatened Dan with bodily harm if he
      showed off again.  So I think we can safely assume that Jim's
      article will continue in the next issue.  

           Announcing the Official C News t-shirt and coffee mug.  All
      contributors to C News get an official C News "Author" t-shirt,
      and a coffee mug.  Anyone else that wants one will have to
      purchase them at cost.  Remember that night at the pizzeria?
      Well this is one of the ideas that came out of the discussion.
      It seems that while Jim Singleton was riding on the steam train
      ride at SOGEAST 89, he started talking to Dave Thompson
      (Micro-Cornucopia Editor) about C News.  It turns out that in
      the early days of MicroC, they used to give T-shirts to
      contributors instead of money.  So after Jim came back from the
      SOG, he dropped the idea of a C News T-shirt.  Well, I thought
      it wasn't a bad idea and now they are available in blue only.
      Next year we will pick another colour.  


      


      Issue                        C News                             3



           Remember the old saying "if you need something done give it
      to the busiest person?"  Well if you don't, I do and that is the
      story of my life these days.  Some of you may have noticed that
      I do not have as big a part in C News as I used to.  It isn't
      that I do not want to, but simply that work commitments are
      taking all of my free time.  However, Jim, Dan and Wayne have
      done a great job of getting this issue of C News together.  With
      their continued support I have no doubt that 1990 will be a
      bigger and better year for C News.  

      Barry 










































      


      Issue                        C News                             4


      ================================================================= 
      MAGAZINE REVIEW - INSIDE TURBO C by Jim Singleton
      ================================================================= 


      (NOTE: I initially reviewed "Inside Turbo C" after the first
      issue, prior to publishing the review, I received issue number
      two.  Therefore, reviews of both issues appear here.) 

      Issue:  Volume 1, Number 1   September 1989
      Publisher:  The Cobb group
                  P.O. Box 24412
                  Louisville, KY  40224-9960

           "Inside Turbo C" is a new newsletter/magazine, published by
      The Cobb Group, Inc.  As the title suggests, the subject matter
      is Turbo C.  At sixteen pages in length, "Inside Turbo C" does
      not take too long to read, especially since approximately half
      of each issue is source code (seven pages in this issue).  While
      the articles are clear and concise, they do not attempt to go
      into any topic in depth.  It will be interesting to see if in
      future issues there are articles which span several issues.  The
      first issue contains articles on interrupts, binary trees, and
      fast screen input/output.  

           As mentioned, each issue contains source code.  My biggest
      complaint, as far as the appearance of the source code, is that
      it is printed with line numbers, which actually makes it look
      somewhat confusing.  In addition, because of the length of each
      issue, none of the articles really explore any topic in any
      great depth.  The biggest problem is that there are errors in
      the source code.  I know this often happens in books and
      magazines, but here we are talking about a newsletter and I
      don't think it should be too hard to check the source code prior
      to publication.  In fact, one listing is incomplete, it's
      missing a number of lines of code.  

           In addition to the newsletter, subscribers also have access
      to Cobb Group Information Services (CGIS) an on-line information
      exchange from The Cobb Group.  The Basic Service, which is free
      to all subscribers, allows the user 15 minutes per day, a back
      issues directory, product news, and an information center.  A
      Premium Service is also available, which allows users to
      download source code, no time limit, on-line conferencing, and
      the features included with the Basic Service.  The Premium
      Service is currently available at an "introductory rate" of $30 
      a year.  

           Speaking of costs, how much is "Inside Turbo C"?  A year's
      subscription costs $59.  Actually, considering that the cover
      price is $7, this represents a savings of $25.  The price is the
      biggest strike against "Inside Turbo C".  It's too expensive for


      


      Issue                        C News                             5


      its size, especially since there are a number of other
      newsletters and magazines devoted to C.  (As a matter of fact,
      you're reading one now.) 

      ------------------------------------------------------------ 

      Issue:  Volume 1, Number 2   October 1989 

           I wasn't too impressed with the first issue, of "Inside
      Turbo C", so how was issue 2?  Don't ask.  Once again, the
      articles are clearly written.  So much for the good news.  

           Actually, the article on spawning a child process isn't too
      bad, nor is the article on conditional compiling.  The article
      on choosing memory models seems out of place.  If the audience
      for "Inside Turbo C" is beginners, which is how the article on
      spawning a child process is written (along with the introduction
      to pointers article and the article on sound generation), this
      article is almost useless.  All this article really is, is a
      definition of each memory model and it takes less than a page to
      explain all of them.  (A much better article on memory models
      appears in issue 11 of the "C News".)  If the information in the
      Turbo C manuals isn't clear, this isn't going to help much
      more.  

           Well, is the source code any better?  The source code for
      the article on pointers is long and hard to follow.  An article
      which is intended as an introduction to pointers should have
      clear and concise examples as source code.  Also, the one
      include file, mcalc.h, makes me think the code is from the
      examples provided by Borland when you purchase Turbo C.  On the
      bright side, it appears that each listing is complete, although
      I didn't try all of the listings.  

      ------------------------------------------------------------ 

      NOTE: Since writing the above, I have received a letter from Tim
      Landgrave, the Product Manager for Technical Journals for the
      Cobb Group, which was sent to all subscribers to "Inside Turbo
      C".  Although it is a bit of an understatement, he admits that
      there are problems with the first two issues of "Inside Turbo
      C".  Although I didn't catch it (probably because I don't have
      the book), one of the examples in the first issue is straight
      out of the book "Turbo Algorithms".  Also, surprise, surprise,
      the program listing for the pointer article is part of the
      Borland Microcalc source code.  Well, because of these and other
      mistakes, all subscriptions to "Inside Turbo C" will begin anew
      with the November issue.  The first volume is considered trash
      ("When your new issue arrives, please throw your old ones
      away."), and the November issue will be volume II, number 1.
      According to Tim, the upcoming issues "will be outstanding in
      every way."  While that remains to be seen, a review of these


      


      Issue                        C News                             6


      upcoming issues of "Inside Turbo C" will appear in an upcoming
      issue of the "C News".  




















































      


      Issue                        C News                             7


      ================================================================= 
      BEGINNERS CORNER by Wayne Dernoncourt    
      ================================================================= 



           In the last column I discussed how to use pointers with the
      "standard" functions found in almost all implementations
      currently in use.  This column is going to extend the discussion
      of pointers with a discussion of just what pointers are and how
      they operate.  

           Most computers operate with certain absolutes, that is,
      there are things that will never change on a specific model or
      brand of computer.  In the case of an IBM PC compatible
      computers, the system clock is at a specific location in memory,
      as are the keyboard buffer and disk drive status locations
      (there are others, but this is not intended to be a
      comprehensive list, just a few examples).  As a programmer you
      will rarely, if ever, have to deal with these specific locations
      -- there are operating system functions which you will use to
      interact with these memory locations -- but they do exist.  

           You can imagine that even if you know the absolute address
      of the memory location that you want to access, it would be
      difficult to tell a compiler that whenever you access the
      variable 'a', you want the computer to access a specific
      location.  In C this is handled through the mechanisms of
      pointers, that is a way for a variable to 'point' to something
      else.  Since the addresses of the examples (the system clock,
      keyboard buffer and disk drive status) are ones that never
      change - you can use the C keyword "const" that says that these
      addresses will never change and that an error is to be signaled
      if your program ever tries to change the address. You can now
      set a variable equal to the value pointed at by the pointer.  

           Let's go back to the example that we started using when
      this series of articles first started off, that of finding the
      average of 4 numbers.  Again we're only going to modify one
      module, the one called GETDATA.  Everything else is going to
      remain the same temporarily.