Box2D Forums

 #import "Box2D.h"
#import <vector>
#import <algorithm>

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

class MyContactListener : public b2ContactListener {

public:
  std::vector<MyContact>_contacts;

MyContactListener();
~MyContactListener();

virtual void BeginContact(b2Contact* contact);
virtual void EndContact(b2Contact* contact);
virtual void PreSolve(b2Contact* contact, const b2Manifold* oldManifold);
virtual void PostSolve(b2Contact* contact, const b2ContactImpulse* impulse);

 };

#import "MyContactListener.h"

MyContactListener::MyContactListener() : _contacts() {
}

MyContactListener::~MyContactListener() {
}

void MyContactListener::BeginContact(b2Contact* contact) {
// We need to copy out the data because the b2Contact passed in
// is reused.
MyContact myContact = { contact->GetFixtureA(), contact->GetFixtureB() };
_contacts.push_back(myContact);
}

void MyContactListener::EndContact(b2Contact* contact) {
    MyContact myContact = { contact->GetFixtureA(), contact->GetFixtureB() };
    std::vector<MyContact>::iterator pos;
    pos = std::find(_contacts.begin(), _contacts.end(), myContact);
    if (pos != _contacts.end()) {
        _contacts.erase(pos);
    }
}

void MyContactListener::PreSolve(b2Contact* contact, const b2Manifold* oldManifold) {
}

void MyContactListener::PostSolve(b2Contact* contact, const b2ContactImpulse* impulse) {
}
 

 // Loop through all of the box2d bodies that are currently colliding, that we have
// gathered with our custom contact listener...
std::vector<b2Body *>toDestroy;
std::vector<MyContact>::iterator pos;
for(pos = _contactListener->_contacts.begin(); pos != _contactListener->_contacts.end(); ++pos) {
    MyContact contact = *pos;

    // Get the box2d bodies for each object
    b2Body *bodyA = contact.fixtureA->GetBody();
    b2Body *bodyB = contact.fixtureB->GetBody();
    if (bodyA->GetUserData() != NULL && bodyB->GetUserData() != NULL) {
        PhysicsSprite *spriteA = (PhysicsSprite *) bodyA->GetUserData();
        PhysicsSprite *spriteB = (PhysicsSprite *) bodyB->GetUserData();

        if (spriteA == sprite  && spriteB == [rope objectAtIndex:0]) {
            b2WeldJointDef weldJointDef;
            weldJointDef.Initialize(bodyA, bodyB, bodyA->GetPosition());
            weldJointDef.collideConnected = false;

            weldJoint = (b2WeldJoint*)world->CreateJoint(&weldJointDef);               

        }
   }
}

Thread 1:EXC_BAD_ACCESS(code=2, address=0x4)

for(pos = _contactListener->_contacts.begin(); pos != _contactListener->_contacts.end(); ++pos)

Apple Mach-O Linker (Id) Error
"MyContactListener::MyContactListener", referenced from:
-[HelloWorldLayer initPhysics] in HelloWorldLayer.o