static void
postStepRemove(cpSpace *space, cpShape *shape, void *unused)
{
  cpSpaceRemoveShape(space, shape);
  cpSpaceRemoveBody(space, shape->body);
  
  cpShapeFree(shape);
  cpBodyFree(shape->body);
}

static int
begin(cpArbiter *arb, cpSpace *space, void *data)
{
  // Get the cpShapes involved in the collision
  // The order will be the same as you defined in the handler definition
  // a->collision_type will be BULLET_TYPE and b->collision_type will be MONSTER_TYPE
  CP_ARBITER_GET_SHAPES(arb, a, b);
  
  // The macro expands exactly as if you had typed this:
  // cpShape *a, *b; cpArbiterGetShapes(arb, &a, &b);
  
  // Add a post step callback to safely remove the body and shape from the space.
  // Calling cpSpaceRemove*() directly from a collision handler callback can cause crashes.
  cpSpaceAddPostStepCallback(space, (cpPostStepFunc)postStepRemove, b, NULL);
  
  // The object is dead, don’t process the collision further
  return 0;
}

#define BULLET_TYPE 1
#define MONSTER_TYPE 2

// Define a collision handler for bullets and monsters
// Kill the monster by removing it’s shape and body from the space as soon as it’s hit by a bullet
cpCollisionHandler *handler = cpSpaceAddCollisionHandler(space, BULLET_TYPE, MONSTER_TYPE);
handler->beginFunc = begin;