How to write a C++ code generator that takes C++ code as input?

Question

We have a CORBA implementation that autogenerates Java and C++ stubs for us. Because the CORBA-generated code is difficult to work with, we need to write wrappers/helpers around the CORBA code. So we have a 2-step code generation process (yes, I know this is bad):

CORBA IDL -> annoying CORBA-generated code -> useful wrappers/helper functions

Using Java's reflection, I can inspect the CORBA-generated code and use that to generate additional code. However, because C++ doesn't have reflection, I am not sure how to do this on the C++ side. Should I use a C++ parser? C++ templates?

TLDR: How to generate C++ code using generated C++ code as input?

Generated from an IDL by a 3rd party CORBA vendor. So the code is in a standard style. — Garrett Hall
– Garrett Hall, Commented Feb 10, 2012 at 16:29

Johnny Willemsen · Accepted Answer · 2019-11-13 14:19:04Z

2

Have you considered to take a step back and use the IDL as source for a custom code generator? Probably you have some wrapper code that hides things like duplicate, var, ptr, etc. We have a Ruby based CORBA IDL compiler that currently generates Ruby and C++ code. That could be extended with a customer generator, see https://www.remedy.nl for RIDL and R2CORBA.

Another option would be to check out the IDL to C++11 language mapping, more details on https://www.taox11.org. This new language mapping is much easier to use and uses standard types and STL containers to work with.

edited Nov 13, 2019 at 14:19

answered Feb 12, 2012 at 13:03

Johnny Willemsen

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3 Comments

Garrett Hall Over a year ago

Thought about it, but never looked for an IDL parser. Thanks!

Johnny Willemsen Over a year ago

What you need is an IDL compiler where you can easily add another backend. Our RIDL compiler is written in Ruby and uses small file that you can edit with any editor and that are then used to generate the code. See R2CORBA and the IDL to C++11 project on OSPortal for example code we generate.

Andrés Senac Over a year ago

Another solution in the same line is to use code.google.com/p/idl4emf. It is an implementation of the IDL grammar and metamodel in the Eclipse Modeling Framework. It contains an example generator project. In code.google.com/p/corbasim you can see an usage example with a partial implementation of the IDL to C++ mapping. We use it for generating additional C++ code from our IDL files.

CapelliC · Accepted Answer · 2012-02-10 16:56:19Z

2

GCC XML could help in recovering the interface.

I'm using it to write a Prolog foreign interface for OpenGL and Horde3D rendering engine.

The interfaces I'm interested to are limited to C, but GCC XML handles C++ as well.

GCC XML parse source code interface and emits and XML AST. Then with an XML library it's fairly easy extract requested info. A nuance it's the lose of macro' symbols: AFAIK just the values survive to the parse. As an example, here (part of ) the Prolog code used to generate the FLI:

make_funcs(NameChange, Xml, FileName, Id) :-
    index_id(Xml, Indexed),

    findall(Name:Returns:ArgTypes,
        (xpath(Xml, //'Function'(@file = Id, @name = Name, @returns = ReturnsId), Function),
         typeid_indexed(Indexed, ReturnsId, Returns),
         findall(Arg:Type, (xpath(Function, //'Argument'(@name = Arg, @type = TypeId), _),
                    typeid_indexed(Indexed, TypeId, Type)), ArgTypes)
        ),
        AllFuncs),

    length(AllFuncs, LAllFuncs),
    writeln(FileName:LAllFuncs),

    fat('prolog/h3dplfi/~s.cpp', [FileName], Cpp),
    open(Cpp, write, Stream),
    maplist(\X^((X = K-A -> true ; K = X, A = []), format(Stream, K, A), nl(Stream)),
        ['#include "swi-uty.h"',
         '#include <~@>'-[call(NameChange, FileName)]
        ]),

    forall(member(F, AllFuncs), make_func(Stream, F)),
    close(Stream).

xpath (you guess it) it's the SWI-Prolog library that make analysis simpler...

edited Feb 10, 2012 at 16:56

answered Feb 10, 2012 at 16:46

CapelliC

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2 Comments

Garrett Hall Over a year ago

Interesting, I don't have to write it in C++ if I use this tool.

Georg Fritzsche Over a year ago

@Garret: There should be similar paths using libclang, e.g. with Python.

Ira Baxter · Accepted Answer · 2012-02-10 17:33:52Z

0

If you want to reliably process C++ source code, you need a program transformation tool that understands C++ syntax and semantics, can parse C++ code, transform the parsed representation, and regenerate valid C++ code (including the original comments). Such a tool provides in effect arbitrary metaprogramming by operating outside the language, so it is not limited by the "reflection" or "metaprogramming" facilities built into the language.

Our DMS Software Reengineering Toolkit with its C++ Front End can do this.

It has been used on a number of C++ automated transformation tasks, both (accidentally) related to CORBA-based activities. The first included reshaping interfaces for a proprietary distributed system into CORBA-compatible facets. The second reshaped a large CORBA-based application in the face of IDL changes; such changes in effect cause the code to be moved around and causes signature changes. You can find technical papers at the web site that describe the first activity; the second was done for a major defense contractor.

answered Feb 10, 2012 at 17:33

Ira Baxter

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2 Comments

user405725 Over a year ago

gccxml got commercialized? :)

Ira Baxter Over a year ago

Much more than GCCXML. GCCXML takes a C++ compiliation unit and produces an XML document containing declarations but not function bodies. OK if you want to know what was defined, and sort of how it was define. Not ok if you want to a) inspect function/method bodies, b) transform definitions or code, c) analyze code flow, d) regenerate source code, e) process anything big (its XML!). I think of GCCXML as only a small part of what DMS does. Last issue: DMS handles lot more langauges than just C++ ... uh, yes, that part about "commercial" is correct.

Davorin Ruševljan · Accepted Answer · 2012-02-11 23:40:18Z

0

Take a look at Clang compiler, aside from being a standalone compiler it is also intended to be used as an library in situations like the one you describe. It will provide you with parse tree on which you could do your analysis and transformations

answered Feb 11, 2012 at 23:40

Davorin Ruševljan

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