C语言 如何用 C 编写 C 编译器？

How can a C compiler be written in C?

提问by jub0bs

This question may stem from a misunderstanding of compilers on my part, but here goes...

这个问题可能源于我对编译器的误解，但这里是......

One can find the following statement in the preface to the first edition of K&R (page xi):

可以在 K&R 第一版（第 xi 页）的序言中找到以下声明：

The operating system, the C compiler, and essentially all UNIX applications programs (including all of the software used to prepare this book) are written in C.

操作系统、C 编译器以及基本上所有 UNIX 应用程序（包括用于编写本书的所有软件）都是用 C 编写的。

(my emphasis)

（我的重点）

Here's what I don't understand: doesn't that C compiler have to be compiled itself before it can compile any C code? And if that C compiler is written in C, wouldn't compiling it require an already existing C compiler?!

这是我不明白的：在编译任何 C 代码之前，C 编译器不是必须自己编译吗？如果那个 C 编译器是用 C 编写的，那么编译它是否需要一个已经存在的 C 编译器？！

The only way out of this infinite-regression conundrum (or chicken-and-egg problem) is that the C compiler written in C that K&R are referring to was actually compiled with an already existing C compiler that was written in a language other than C. The C compiler written in C then superseded the latter.

解决这个无限回归难题（或先有鸡还是先有蛋的问题）的唯一方法是，K&R 所指的用 C 语言编写的 C 编译器实际上是用现有的 C 编译器编译的，而该编译器是用 C 以外的语言编写的. 用C 编写的C 编译器随后取代了后者。

Or am I completely off?

还是我完全没了？

采纳答案by Yu Hao

It's called Bootstrapping, quoting from Wikipedia:

它被称为Bootstrapping，引用自维基百科：

If one needs a compiler for language X to obtain a compiler for language X (which is written in language X), how did the first compiler get written? Possible methods to solving this chicken or the egg problem include:

如果需要语言 X 的编译器来获得语言 X 的编译器（用语言 X 编写），那么第一个编译器是如何编写的？解决这个鸡或蛋问题的可能方法包括：

1. Implementing an interpreter or compiler for language X in language Y. Niklaus Wirth reported that he wrote the first Pascal compiler in Fortran.
2. Another interpreter or compiler for X has already been written in another language Y; this is how Scheme is often bootstrapped.
3. Earlier versions of the compiler were written in a subset of X for which there existed some other compiler; this is how some supersets of Java, Haskell, and the initial Free Pascal compiler are bootstrapped.
4. The compiler for X is cross compiled from another architecture where there exists a compiler for X; this is how compilers for C are usually ported to other platforms. Also this is the method used for Free Pascal after the initial bootstrap.
5. Writing the compiler in X; then hand-compiling it from source (most likely in a non-optimized way) and running that on the code to get an optimized compiler. Donald Knuth used this for his WEB literate programming system.

1. 用 Y 语言实现 X 语言的解释器或编译器。 Niklaus Wirth 报告说他用 Fortran 编写了第一个 Pascal 编译器。
2. X 的另一个解释器或编译器已经用另一种语言 Y 编写；这就是 Scheme 经常被引导的方式。
3. 早期版本的编译器是用 X 的一个子集编写的，其中存在一些其他编译器；这就是 Java、Haskell 和最初的 Free Pascal 编译器的一些超集是如何引导的。
4. X 的编译器是从另一个存在 X 编译器的体系结构交叉编译的；这就是 C 编译器通常被移植到其他平台的方式。这也是在初始引导后用于 Free Pascal 的方法。
5. 用 X 编写编译器；然后从源代码手动编译它（很可能以非优化的方式）并在代码上运行它以获得优化的编译器。Donald Knuth 将其用于他的 WEB 文学编程系统。

And if you are interested, hereis Dennis Richie's first C compiler source.

如果您有兴趣，这里是 Dennis Richie 的第一个 C 编译器源代码。

回答by Pascal Cuoq

See the Chicken and Egg section of the Wikipedia page:

请参阅维基百科页面的鸡肉和鸡蛋部分：

If one needs a compiler for language X to obtain a compiler for language X (which is written in language X), how did the first compiler get written? Possible methods to solving this chicken or the egg problem include:

如果需要语言 X 的编译器来获得语言 X 的编译器（用语言 X 编写），那么第一个编译器是如何编写的？解决这个鸡或蛋问题的可能方法包括：

• Implementing an interpreter or compiler for language X in language Y. Niklaus Wirth reported that he wrote the first Pascal compiler in Fortran.
• Another interpreter or compiler for X has already been written in another language Y; this is how Scheme is often bootstrapped.
• Earlier versions of the compiler were written in a subset of X for which there existed some other compiler; this is how some supersets of Java, Haskell, and the initial Free Pascal compiler are bootstrapped.
• The compiler for X is cross compiled from another architecture where there exists a compiler for X; this is how compilers for C are usually ported to other platforms. Also this is the method used for Free Pascal after the initial bootstrap.
• Writing the compiler in X; then hand-compiling it from source (most likely in a non-optimized way) and running that on the code to get an optimized compiler. Donald Knuth used this for his WEB literate programming system.

• 用 Y 语言实现 X 语言的解释器或编译器。 Niklaus Wirth 报告说他用 Fortran 编写了第一个 Pascal 编译器。
• X 的另一个解释器或编译器已经用另一种语言 Y 编写；这就是 Scheme 经常被引导的方式。
• 早期版本的编译器是用 X 的一个子集编写的，其中存在一些其他编译器；这就是 Java、Haskell 和最初的 Free Pascal 编译器的一些超集是如何引导的。
• X 的编译器是从另一个存在 X 编译器的体系结构交叉编译的；这就是 C 编译器通常被移植到其他平台的方式。这也是在初始引导后用于 Free Pascal 的方法。
• 用 X 编写编译器；然后从源代码手动编译它（很可能以非优化的方式）并在代码上运行它以获得优化的编译器。Donald Knuth 将其用于他的 WEB 文学编程系统。

回答by perror

Usually, a first compiler is written in another language (directly in PDP11 assembler in this case, or in C for most of the "modern" languages). Then, this first compiler is used to program a compiler written in the language itself.

通常，第一个编译器是用另一种语言编写的（在这种情况下直接用 PDP11 汇编程序编写，或者对于大多数“现代”语言用 C 编写）。然后，第一个编译器用于编写用语言本身编写的编译器。

You can read this pageabout the history of the C language. You will see that it is also strongly linked to the UNIX system.

您可以阅读有关 C 语言历史的页面。您将看到它也与 UNIX 系统紧密相连。

回答by Jon Kiparsky

It's perfectly ordinary for a compiler to be written in the language it compiles. One way to achieve this would be to write a complete compiler for language L in some other language, and then to write a new compiler for L in L. A more interesting approach would be to write a minimal compiler for a subset of L in some other language, and then use this minimal subset to improve the compiler, making it less minimal increasing the available subset of L. In this way, a complete compiler can be built.

用它编译的语言编写编译器是很正常的。实现这一点的一种方法是用其他语言为语言 L 编写一个完整的编译器，然后在 L 中为 L 编写一个新的编译器。 一个更有趣的方法是为某些语言中的 L 的子集编写一个最小编译器其他语言，然后使用这个最小子集来改进编译器，使其最小化增加 L 的可用子集。这样，就可以构建一个完整的编译器。