Reference pointers to C++ objects in swift?

Question

I'm working on a swift project which incorporates a C++ library (bullet physics). Currently I achieve this by wrapping the C++ library with Objective-C, and then using the Objectve-C Code in Swift via bridging header.

I would like to eliminate the Objective-C wrapper, and access Bullet through a pure C interface in the interest of making the code more platform agnostic.

Conceptually, I understand how to create a C interface for C++ code by using extern "C", but I don't know how to make the types from the C++ library available in my Swift Code.

For instance, I would like to be able to do something like this:

// MyPhysicsObject.swift

class MyPhysicsObject {

    let rigidBody: btRigidBody

    init() {
        self.rigidBody = createRigidBody()  //called from C interface
    }

}

With a C header file:

// BulletCInterface.h

#ifdef __cplusplus
extern "C" {
#endif

btRigidBody* createRigidBody();

#ifdef __cplusplus
}
#endif

And a C++ implementation file:

//BulletCInterface.cpp

#import <BulletDynamics/btBulletCollisionCommon.h>
#import <BulletDynamics/btBulletDynamicsCommon.h>

#ifdef __cplusplus
extern "C" {
#endif

btRigidBody* createRigidBody() {
   //invoke the C++ bullet API to produce a btRigid body
   //...
}

#ifdef __cplusplus
}
#endif

But when I attempt this, the compiler complains that btRigidBody is an undefined type in BulletCInterface.h. At a minimum I would like to be able to hold references to these objects in swift, and at best I would like to be able to access their data members (like mass etc.)

How can I expose these C++ types to my Swift code? Or do I have to just make everything a void* and keep track of types myself?

Anatoli P · Accepted Answer · 2016-10-25 02:11:14Z

As stated in Swift documentation, "You cannot import C++ code directly into Swift. Instead, create an Objective-C or C wrapper for C++ code." See https://developer.apple.com/library/content/documentation/Swift/Conceptual/BuildingCocoaApps/.

If you want to keep Objective-C out of the picture, then you need a C wrapper, which is what you are trying to do. You need to wrap C++ types in the C interface callable from Swift. The error about btRigidBody is due to the type not being wrapped. I'm assuming it is a C++ type and its definition is unavailable in the C interface header. If you include a header that defines that type in BulletCInterface.h, that won't work because then it won't be usable in Swift via a bridging header.

The wrapper C interface could have functions that map to methods and data members of the C++ classes you use.

BTW, you don't need #ifdef __cplusplus in BulletCInterface.cpp, just do

// This should return a C wrapper for the btRigidBody C++ type
extern "C" btRigidBodyWrapper* createRigidBody() {
    ...
}

It's all C++ code, so you can use extern "C" without the pre-processor conditionals.

Hopefully this is helpful.

Collectives™ on Stack Overflow

Reference pointers to C++ objects in swift?

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related