Re: Struct in C and C++

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Thu, 15 Jun 2006 15:33:14 -0400

Message-ID:

<e6sclt$sjn$1@news.datemas.de>

Greg wrote:

Victor Bazarov wrote:

Greg wrote:

[...]
Actually the first C++ compiler was itself written in C++ - which
might sound like a chicken-and-egg impossibility were it not for one
fact: the first C++ compiler (CFront) did not actually compile C++
source code (including its own) directly - rather it first
translated C++ source code into C and then compiled the translated
sources with a C compiler. Pretty simple, isn't it?

I think you're confused. "Compile C++" and "translate C++" are
pretty much the same thing. So, how could it have been written in
C++? What would be used to translate its own code from C++ "into
C"? And if it wasn't used itself, what was used? And if, in fact,
some other thing was used, what do you call it if not "C++
translator"? And what was that thing written in? Catch my drift?
There is no "chicken and egg" problem. The "chicken and egg"
conundrum exists when there is circular dependency. There is none
here. First C++ compiler/translator was most likely written in C
(or C With Classes or some other predecessor of the "real C++").
After than each next version of a C++ compiler is written in C++
probably (because the C++ compiler programmers know C++ the best),
and any new advanced features the next version implements are simply
not used to write it (because the compiler does not support them).
That's just evolution of tools. For example, what debugger is used
to debug a debugger?

The first C++ compiler was written in C++. It compiled itself. From
Wikipedia:

"As Cfront was written in C++, it was a challenge to bootstrap on a
machine without a C++ compiler/translator. Along with the Cfront C++
sources,

....let's call them 'a'..

a special "half-preprocessed" version of the C code

....let's call it 'b'...

resulting
from compiling Cfront with itself

[huh! very interesting!]

was also provided. This C code was
to be compiled with the native C compiler, and the resulting
executable could then be used to compile the Cfront C++ sources."

I wasn't aware (although I now think it was unfounded) that Wikipedia
contains such convoluted and misleading "explanations".

How could Cfront compile itself?

   struct Cfront {
      CfrontSources a;
      HalfProcessedC b;

      Cfront() : a(typed_up()), b(Cfont().compile(Cfront())) {}
   };

Take a look at the constructor initialiser list. Notice the recursion?
It's infinite!

V
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