Question

I’m trying to get this C++ method to return an array of b2Fixture instances. It iterates of a series of JRContact instances, which are defined like:

struct JRContact {
    b2Fixture *fixtureA;
    b2Fixture *fixtureB;
    bool operator==(const JRContact& other) const
    {
        return (fixtureA == other.fixtureA) && (fixtureB == other.fixtureB);
    }
};

n.b. I’m a total stranger to C++, don’t hesitate to mention weird things I might have done in that code 😉

The following fails to compile (XCode compiler on MacOS), see errors in comments:

id AbstractContactListener::getFixturesOfTypeCollidingWithFixture(b2Fixture *fix, int type){

    std::vector<b2Fixture> fixtures;

    std::vector<JRContact>::iterator ct;
    JRContact contact;

    for (ct = _contacts.begin(); ct != _contacts.end(); ct++){

        contact = *ct;

        if ( 
                ( (fix == contact.fixtureA) || (fix == contact.fixtureB) ) &&
                ( contactContainsType(contact, type) )
            ){

            if (fix == contact.fixtureA) {

                // error: Semantic Issue: Reference to type 'const value_type' (aka 'const b2Fixture') could not bind to an lvalue of type 'b2Fixture *'

                fixtures.push_back(contact.fixtureB);
            }

            else {

                // error: Semantic Issue: Reference to type 'const value_type' (aka 'const b2Fixture') could not bind to an lvalue of type 'b2Fixture *'
                fixtures.push_back(contact.fixtureA);
            }
        }
    }

    // error: Semantic Issue: No viable conversion from 'std::vector<b2Fixture>' to 'id'
    return fixtures;
}

Thanks for your time!

Answer 1

Change :

std::vector<b2Fixture> fixtures;

to :

std::vector<b2Fixture *> fixtures;

About the return type you can change it either to void* or std::vector<b2Fixture *> * and use : return &fixtures;

But pay attention the your vector is local so allocate it for not returning a pointer to an invalid location. (And ofcourse remember to free it when you done using it).