Java 仮想マシンと Windows は両方とも C++ で書かれています。なぜ Linux カーネルは C++ ではなく C を使用するのですか? php インタープリターと python インタープリターが c++ ではなく c を使用するのはなぜですか? PHP や Python は Java 仮想マシンよりも簡単で、Linux は Windows よりも簡単ということですか?
<code class="language-text">On Wed, 5 Sep 2007, Dmitry Kakurin wrote: > > When I first looked at Git source code two things struck me as odd: > 1. Pure C as opposed to C++. No idea why. Please don't talk about portability, > it's BS. *YOU* are full of bullshit. C++ is a horrible language. It's made more horrible by the fact that a lot of substandard programmers use it, to the point where it's much much easier to generate total and utter crap with it. Quite frankly, even if the choice of C were to do *nothing* but keep the C++ programmers out, that in itself would be a huge reason to use C. In other words: the choice of C is the only sane choice. I know Miles Bader jokingly said "to piss you off", but it's actually true. I've come to the conclusion that any programmer that would prefer the project to be in C++ over C is likely a programmer that I really *would* prefer to piss off, so that he doesn't come and screw up any project I'm involved with. C++ leads to really really bad design choices. You invariably start using the "nice" library features of the language like STL and Boost and other total and utter crap, that may "help" you program, but causes: - infinite amounts of pain when they don't work (and anybody who tells me that STL and especially Boost are stable and portable is just so full of BS that it's not even funny) - inefficient abstracted programming models where two years down the road you notice that some abstraction wasn't very efficient, but now all your code depends on all the nice object models around it, and you cannot fix it without rewriting your app. In other words, the only way to do good, efficient, and system-level and portable C++ ends up to limit yourself to all the things that are basically available in C. And limiting your project to C means that people don't screw that up, and also means that you get a lot of programmers that do actually understand low-level issues and don't screw things up with any idiotic "object model" crap. So I'm sorry, but for something like git, where efficiency was a primary objective, the "advantages" of C++ is just a huge mistake. The fact that we also piss off people who cannot see that is just a big additional advantage. If you want a VCS that is written in C++, go play with Monotone. Really. They use a "real database". They use "nice object-oriented libraries". They use "nice C++ abstractions". And quite frankly, as a result of all these design decisions that sound so appealing to some CS people, the end result is a horrible and unmaintainable mess. But I'm sure you'd like it more than git. Linus </code>
<code class="language-c"><span class="cp">#include <stdio.h></span>
<span class="cm">/*</span>
<span class="cm"> * min()/max() macros that also do</span>
<span class="cm"> * strict type-checking.. See the</span>
<span class="cm"> * "unnecessary" pointer comparison.</span>
<span class="cm"> */</span>
<span class="cp">#define min(x,y) ({ \</span>
<span class="cp"> typeof(x) _x = (x); \</span>
<span class="cp"> typeof(y) _y = (y); \</span>
<span class="cp"> (void) (&_x == &_y); \</span>
<span class="cp"> _x < _y ? _x : _y; })</span>
<span class="kt">int</span> <span class="nf">main</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span>
<span class="p">{</span>
<span class="kt">int</span> <span class="n">a</span> <span class="o">=</span> <span class="mi">3</span><span class="p">,</span> <span class="n">b</span> <span class="o">=</span> <span class="mi">5</span><span class="p">;</span>
<span class="kt">double</span> <span class="n">d1</span> <span class="o">=</span> <span class="mf">3.14</span><span class="p">,</span> <span class="n">d2</span> <span class="o">=</span> <span class="mf">2.718</span><span class="p">;</span>
<span class="n">printf</span><span class="p">(</span><span class="s">"min of a & b: %d</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">min</span><span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="n">b</span><span class="p">));</span>
<span class="n">printf</span><span class="p">(</span><span class="s">"min of d1 & d2: %lf</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">min</span><span class="p">(</span><span class="n">d1</span><span class="p">,</span> <span class="n">d2</span><span class="p">));</span>
<span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</code><code class="language-text">The reasons specifically for Linux are explained in great detail as part of the Linux Kernel Mailing List (LKML) Frequently Asked Questions (FAQ) at: http://www.tux.org/lkml/ Scroll down to section 15 (titled Programming Religion) and read the explanation. A summary is: - Linus started with an 386 computer, Minix, and gcc (no g++ available) - C is used instead of Assembly for a LOT of reasons (maintenance, readability, efficiency, ...) - it is not clear how an object oriented language helps in OS design - MANY years ago, they tried using g++ to compile the Linux kernel and found it ran slower than when compiled with gcc (many thought it should have been the same); they are not willing to do this again - Linus makes the final decision and he's decided to stick with C There is also another good explanation of some of the issues at http://kerneltrap.org/node/2067 which describes one person's attempt to build adapt some C++ code to incorporate into a kernel module. For a historical perspective, Thompson and Ritchie developed Unix using some of the concepts from Multics and CTSS http://www.multicians.org/unix.html including implementation of most operations in a higher order language (Unix - C, Multics - PL/I), common naming of commands, etc. I also refer you to http://cm.bell-labs.com/cm/cs/who/dmr/hist.html which describes the EARLY development of Unix including the conversion from Assembly on the PDP-7 to C on the PDP-11 (near the end of the paper). Building from that basis, the Unix from AT&T that was widely distributed and worked on by thousands of people was a C based operating system. In the 1970's and 1980's, an alternative to AT&T's distribution was developed at UC Berkeley, see http://en.wikipedia.org/wiki/Berkeley_Software_Distribution for a relatively short explanation of the development of BSD. The BSD version eventually did not use ANY of the AT&T code base, but was also implemented in C. At the end of the article is a list of several BSD descendants including SunOS (now Solaris). That is not to say that some applications are better implemented in an OO language such as C++. There are several Graphical User Interface (GUI) toolkits such as KDE which are implemented in C++. However, there are applications that are better suited for a more procedural language, and at this point operating systems are in that category. If this answer is unclear or somehow incomplete, please make a clarification request. Good luck with your work. --Maniac </code>
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