How to convert C Code to C

Question

I have some C   code   In the code there are many classes defined  their member functions  constructors  destructors for those classes  few template classes and lots of C   stuff  Now I need to convert the source to plain C code    I the have following questions    Is there any tool to convert C   code and header files to C code  Will I have to do total rewrite of the code  I will have to remove the constructors destructors and move that code into some init    deinit   functions  change classes to structures  make existing member functions as function pointers in those newly defined structures and then invoke those functions using function pointers etc      If I have to convert it manually myself  what C   specific code-data constructs semantics do I need to pay attention to while doing the conversion from C   to C

User · Answer

This is an old thread but apparently the C++ Faq has a section (Archived 2013 version) on this. This apparently will be updated if the author is contacted so this will probably be more up to date in the long run, but here is the current version:

Depends on what you mean. If you mean, Is it possible to convert C++ to readable and maintainable C-code? then sorry, the answer is No — C++ features don't directly map to C, plus the generated C code is not intended for humans to follow. If instead you mean, Are there compilers which convert C++ to C for the purpose of compiling onto a platform that yet doesn't have a C++ compiler? then you're in luck — keep reading.

A compiler which compiles C++ to C does full syntax and semantic checking on the program, and just happens to use C code as a way of generating object code. Such a compiler is not merely some kind of fancy macro processor. (And please don't email me claiming these are preprocessors — they are not — they are full compilers.) It is possible to implement all of the features of ISO Standard C++ by translation to C, and except for exception handling, it typically results in object code with efficiency comparable to that of the code generated by a conventional C++ compiler.

Here are some products that perform compilation to C:

Comeau Computing offers a compiler based on Edison Design Group's front end that outputs C code.

LLVM is a downloadable compiler that emits C code. See also here and here. Here is an example of C++ to C conversion via LLVM.

Cfront, the original implementation of C++, done by Bjarne Stroustrup and others at AT&T, generates C code. However it has two problems: it's been difficult to obtain a license since the mid 90s when it started going through a maze of ownership changes, and development ceased at that same time and so it doesn't get bug fixes and doesn't support any of the newer language features (e.g., exceptions, namespaces, RTTI, member templates).

Contrary to popular myth, as of this writing there is no version of g++ that translates C++ to C. Such a thing seems to be doable, but I am not aware that anyone has actually done it (yet).

Note that you typically need to specify the target platform's CPU, OS and C compiler so that the generated C code will be specifically targeted for this platform. This means: (a) you probably can't take the C code generated for platform X and compile it on platform Y; and (b) it'll be difficult to do the translation yourself — it'll probably be a lot cheaper/safer with one of these tools.

One more time: do not email me saying these are just preprocessors — they are not — they are compilers.

User · Answer

There is indeed such a tool  Comeau s C   compiler    It will generate C code which you can t manually maintain  but that s no problem  You ll maintain the C   code  and just convert to C on the fly

User · Answer

While you can do OO in C  e g  by adding a theType  this first parameter to methods  and manually handling something like vtables for polymorphism  this is never particularly satisfactory as a design  and will look ugly  even with some pre-processor hacks    I would suggest at least looking at a re-design to compare how this would work out   Overall a lot depends on the answer to the key question  if you have working C   code  why do you want C instead

User · Answer

http   llvm org docs FAQ html translatecxx It handles some code  but will fail for more complex implementations as it hasn t been fully updated for some of the modern C   conventions   So try compiling your code frequently until you get a feel for what s allowed  Usage sytax from the command line is as follows for version 9 0 1  clang -c CPPtoC cpp -o CPPtoC bc -emit-llvm clang -march c  CPPtoC bc -o CPPtoC c  For older versions  unsure of transition version   use the following syntax  llvm-g   -c CPPtoC cpp -o CPPtoC bc -emit-llvm llc -march c  CPPtoC bc -o CPPtoC c  Note that it creates a GNU flavor of C and not true ANSI C   You will want to test that this is useful for you before you invest too heavily in your code   For example  some embedded systems only accept ANSI C  Also note that it generates functional but fairly unreadable code   I recommend commenting and maintain your C   code and not worrying about the final C code  EDIT   although official support of this functionality was removed  but users can still use this unofficial support from Julia language devs  to achieve mentioned above functionality

User · Answer

Maybe good ol  cfront will do

User · Answer

A compiler consists of two major blocks  the  front end  and the  back end   The front end of a compiler analyzes the source code and builds some form of a  intermediary representation  of said source code which is much easier to analyze by a machine algorithm than is the source code  i e  whereas the source code e g  C   is designed to help the human programmer to write code  the intermediary form is designed to help simplify the algorithm that analyzes said intermediary form easier   The back end of a compiler takes the intermediary form and then converts it to a  target language    Now  the target language for general-use compilers are assembler languages for various processors  but there s nothing to prohibit a compiler back end to produce code in some other language  for as long as said target language is  at least  as flexible as a general CPU assembler   Now  as you can probably imagine  C is definitely as flexible as a CPU s assembler  such that a C   to C compiler is really no problem to implement from a technical pov   So you have  C   ---frontEnd---  someIntermediaryForm ---backEnd---  C  You may want to check these guys out  http   www edg com index php location c frontend  the above link is just informative for what can be done  they license their front ends for tens of thousands of dollars   PS As far as i know  there is no such a C   to C compiler by GNU  and this totally beats me  if i m right about this   Because the C language is fairly small and it s internal mechanisms are fairly rudimentary  a C compiler requires something like one man-year work  i can tell you this first hand cause i wrote such a compiler myself may years ago  and it produces a  virtual  stack machine intermediary code   and being able to have a maintained   up-to-date C   compiler while only having to write a C compiler once would be a great thing to have

[c++] How to convert C++ Code to C

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