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How could the first C++ compiler be written in C++?

I know my question goes to the underground galaxy cave where languages are born and involves some lambda math and light-years of google-studying. But what kind of knowledge is necessary to create a language?

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    Possible duplicate: "Chickens come from eggs but eggs come from chickens, how is this possible?" :) Mar 26, 2012 at 15:48
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    1st appear: "the CREATOR", 2nd to get in: "the egg." 3rd and last "the chicken" . Learned from this guys, they are very funny!
    – H_7
    Mar 26, 2012 at 16:09
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    Unless you are from the Star Wars universe (where parsecs are apparently units for measuring time and not distance), you could change that to "years of google studying" :-)
    – Francesco
    Mar 26, 2012 at 16:35
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    @Francesco I am from Star Wars universe, nice to meet you.
    – H_7
    Mar 26, 2012 at 22:00
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    Vote to reopen, the best answer in the other question seems fairly C++ specific. C != C++. Also, the question here seems like it might be a tad more general.
    – Doug T.
    Mar 27, 2012 at 21:45

4 Answers 4


Look up "bootstrapping".

Basically you start with a very minimal process/set of functions that can be used to compile the code that defines a slightly more functional compiler. This creates your next compiler which then can then be used to build code that can do even more. You repeat this process until you have a full blown compiler that can compile all the language features.

The other alternative is to write the first version of the compiler in a different language and then write the next version in your target language.

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    I've always been baffled by the idea of a compiler being able to compile itself, but that cleared it up quite a bit. Thanks!
    – Andy Hunt
    Mar 26, 2012 at 15:07
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    The very first compiler may be written in another language too, and then rewritten as soon the new compiler has enough features.
    – marcus
    Mar 26, 2012 at 15:10
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    It would be really interesting to see a list of self-compiling languages, as well as the languages they were originally written in.
    – Plutor
    Mar 26, 2012 at 15:23
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    @mcmcc That would be the scenario described in Reflections on Trusting Trust, written by Ken Thompson. Whether or not anyone's actually snuck code like that into a mainstream compiler is questionable.
    – Tacroy
    Mar 26, 2012 at 15:53
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    When two compilers love each other very much...
    – Joe
    Mar 26, 2012 at 22:41

ChrisF's answer is excellent, but I wanted to add this example that always stuck by me after my computer science course on bootstrapping.

Suppose you have a basic C compiler that does not support escape codes for strings yet, and you wanted to add that. You could add a snippet of code similar to this:

if( str[i] == 0x5c ) {       // ASCII code for backslash
   switch( str[i+1] ) {
      case 'n': return 0x0a; // ASCII code for new line
      case 't': return 0x09; // ASCII code for tab
      // ...                 // more ASCII code for other escapes
      default: return str[i+1];

After you have added this to the compiler, and generated a new compiler binary, you could then rewrite this into:

if( str[i] == '\\' ) { 
   switch( str[i+1] ) {
      case 'n': return '\n';
      case 't': return '\t';
      // ...
      default: return str[i+1];

That would remove any knowledge about ASCII codes from the compiler source code, but the compiler would still magically generate the correct codes.


Bootstrapping is definitely the standard way to build a compiler today. But remember that you don't need a compiler or interpreter to write a program in a language. For instance, Christopher Strachey wrote a famous AI program that was able to play Checkers in CPL before there was a compiler for CPL. He had to translate the program to machine code "manually", which is tedious and error-prone, but not really difficult (that's why computers can do it so well).

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    That would be named the "human compiler", right? Mar 26, 2012 at 15:52
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    its not really accurate to say there was no compiler, manual compilation makes you the compiler.
    – Ryathal
    Mar 26, 2012 at 15:55
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    @Ryathal: According to wikipedia, "A compiler is a computer program (or set of programs) that transforms source code ...". So, since a human being isn't a computer program, a human can't be a compiler ;-)
    – nikie
    Mar 26, 2012 at 16:47
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    Wikipedia can't possibly be wrong
    – Chris
    Nov 23, 2015 at 4:03

I hope this is not out of topic, but I wanted to point out that, once you have one C compiler for one platform X, bootstrapping for other platforms can be done by using cross-compilation:

  • You have a C compiler c1 for architecture X that runs on architecture X.
  • You write a C compiler c2 for architecture Y, written in C.
  • You compile the compiler c2 on X using c1 and obtain the binary for compiler c2 that runs on X.
  • You use the binary for c2 that runs on X to compile itself and obtain a binary of c2 that will run on Y.

In other words, when you have the first egg, it is easy to make more eggs.


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