Create automatic C wrapper for C++ library?

Question

Let say I have a C++ DLL. AFAIK, there is no widely-adopted ABI standard for C++, therefore to make sure it works and does not depend on the compiler of the target application I would need to wrap my library in a C interface.

Are there any tools that can automatically generate such interface? Would also be nice if they could generate wrappers around C interface to look as if they are original C++ objects, e.g.

Foo* f = new Foo();  // FooWrapper* fw = Foo_create();
f->bar("test");      // Foo_bar(fw, "test")

translates into C functions that are invoked in my library using generated C ABI. I understand that C++ is fairly complicated language and not everything can be easily wrapped in a C interface, but I was wondering if there are any such solutions that even support a subset of the C++ language (maybe with the help of some manually written IDL/XML files)?

Answer 1

If you want a way to make C++ code callable from other compilers/standard libraries, you can use cppcomponents from https://github.com/jbandela/cppcomponents. Full disclosure - I am the author of the library.

Here is a simple hello world example

First make a file called library.h In this file you will define the Component

#include <cppcomponents/cppcomponents.hpp>

struct IPerson
:public cppcomponents::define_interface<cppcomponents::uuid<0xc618fd04,0xaa62,0x46e0,0xaeb8,0x6605eb4a1e64>>
{

    std::string SayHello();

    CPPCOMPONENTS_CONSTRUCT(IPerson,SayHello);



};

inline std::string PersonId(){return "library!Person";}

typedef cppcomponents::runtime_class<PersonId,cppcomponents::object_interfaces<IPerson>> Person_t;
typedef cppcomponents::use_runtime_class<Person_t> Person;

Next create library.cpp In this file you will implement the interface and component

#include "library.h"

struct PersonImplementation:cppcomponents::implement_runtime_class<PersonImplementation,Person_t>
{

    std::string SayHello(){return "Hello World\n";}

};

CPPCOMPONENTS_DEFINE_FACTORY(PersonImplementation);

Finally here is you main program (call it example1.cpp) that uses your implementation

#include "library.h"
#include <iostream>

int main(){
    Person p;
    std::cout << p.SayHello();

}

To build the program you will need to download cppcomponents (just clone from the git link above). It is a header only library and needs only a c++11 compiler.

Here is how you would build it on Windows

cl /EHsc example1.cpp /I pathtocppcomponents

g++ -std=c++11 library.cpp -o library.dll -shared -I pathtocppcomponents

where pathocppcomponents is the directory of cppcomponents. I am assuming you have cl and g++ in your path.

To run the program, make sure library.dll is in the same directory as example1.exe and run example1.exe

This library requires fairly compliant c++11 support, so it needs MSVC 2013 Preview, and at least g++ 4.7. This library works on both Windows and Linux.