Linux カーネルが C++ ではなく C を使用するのはなぜですか?

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?

返信内容:

技術的な観点から推測してみましょう:

コンパイルされたマシン コードの制御の程度の観点からは、C は C++ よりもはるかに優れています。システム プログラマは、C を見たときに、コンパイラから出力されるアセンブリ コードがどのようなものであるかをほとんど知りません。 C++ コンパイラから出力されるものはさらに複雑で、オブジェクト このポインターに加えて、さまざまな仮想テーブル、そしてもちろんさまざまなコピー構造などが含まれます。完全にコントロールするのは実は簡単ではありません。 (私はオペレーティングシステムのカーネルを書いたことはありませんが、オペレーティングシステムのカーネルはアセンブリによって制御されるべきであり、c を使用するのは開発効率を向上させるためだけであると常々感じています。)

高レベルの観点からC++の言語機能、テンプレート、ポリモーフィズムなどの機能をシステム開発で使うべきか、使わないべきか？これは非常に現実的な問題です。これらの高度な機能を適切に制御できないと、コンパイルされたコードが肥大化したり、最悪の場合、奇妙な問題が発生したりすることがあります。そして、カーネルのデバッグとアプリケーションのデバッグはまったく別のものです... したがって、bochs は C++ に変換されましたが、開発手順ではテンプレートの使用を許可しないことが明確に要求されています。

最後の点は無視できません。Linux カーネルはクロスプラットフォームであり、適切に最適化する必要があります。すべてのプラットフォームに C++ コンパイラーがあるわけではありません。また、たとえあったとしても、最適化効率はそれほど高くない可能性があります。

もちろん、ライナスの個人的な好き嫌いなど、他の要因もあります... 1. Windows カーネルも C です。ここ数年、少しだけ C++ を使い始めましたが、基本的にはクラス付きの C しか使いません。
2. Linus は個人的に C++ を嫌います。
3. Linux カーネルは 1991 年に発表され、C++ は 1998 年まで完成しませんでした。
4. 言語は、書かれている内容が簡単かどうかとは関係ありません。 オペレーティング システムのカーネルは、コンピュータが何をしているのかを明示的に知る必要がある必要がある数少ない状況の 1 つであり、C の使用はその数少ないオプションの 1 つです。 Linux からの公式の回答 (元の質問では、なぜ git が C++ ではなく C で書かれているのかが尋ねられましたが、そこに記載されている理由も質問に当てはまります):

<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>

まず、2 つの「非常に長いコード」から始めたいと思います。
次のコードは min.c と呼ばれます:

<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>

この質問も当時私を悩ませました。なぜ Linux カーネルは C++ を導入しなかったのですか? これはお気に入りの答えです。

<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>

ライナスは C++ が好きではありません レベルが低く、信頼性が高く、安定しています。 ライナスに聞いて、顔にスプレーしてくれるか聞いてみてください (▭-▭)✧ C++は自由すぎる。オペレーティング システムのカーネルを書くことに慣れていますか?