std::string constructor corrupts pointer - c++

Question

I have an Entity class, which contains 3 pointers: m_rigidBody, m_entity, and m_parent. Somewhere in Entity::setModel(std::string model), it's crashing. Apparently, this is caused by bad data in m_entity. The weird thing is that I nulled it in the constructor and haven't touched it since then. I debugged it and put a watchpoint on it, and it comes up that the m_entity member is being changed in the constructor for std::string that's being called while converting a const char* into an std::string for the setModel call. I'm running on a Mac, if that helps (I think I remember some problem with std::string on the Mac). Any ideas about what's going on?
EDIT: Here's the code for GEntity:
GEntity::GEntity(GWorld* world, unsigned long int idNum) {
GEntity(world, idNum, btTransform::getIdentity());
}
GEntity::GEntity(GWorld* world, unsigned long int idNum, btTransform trans) : m_id(idNum), m_trans(trans), m_world(world) {
// Init unused properties
m_rigidBody = NULL;
m_entity = NULL; // I'm setting it here
m_parent = NULL;
// Find internal object name
std::ostringstream ss;
ss << "Entity" << idNum << "InWorld" << world;
m_name = ss.str();
// Create a scene node
m_sceneNode = m_world->m_sceneMgr->getRootSceneNode()->createChildSceneNode(m_name+"Node");
// Initialize the SceneNode's transformation
m_sceneNode->setPosition(bv3toOv3(m_trans.getOrigin()));
m_sceneNode->setOrientation(bqToOq(m_trans.getRotation()));
}
void GEntity::setModel(std::string model) {
m_model = model;
// Delete entity on model change
if(m_entity != NULL) { // And by the time this line comes around, it's corrupt
m_world->m_sceneMgr->destroyEntity(m_entity);
m_entity = NULL;
}
// Create new entity with given model
m_entity = m_world->m_sceneMgr->createEntity(m_name+"Ent", model);
// Apply a new rigid body if needed
if(m_rigidBody != NULL) {
initPhysics();
}
}
void GEntity::initPhysics() {
deinitPhysics();
}
void GEntity::deinitPhysics() {
if(m_rigidBody != NULL) {
m_world->m_dynWorld->removeRigidBody(m_rigidBody);
delete m_rigidBody;
m_rigidBody = NULL;
}
}
And here's the definition of GEntity:
class GEntity : public btMotionState {
public:
GEntity(GWorld* world, unsigned long int idNum);
GEntity(GWorld* world, unsigned long int idNum, btTransform trans);
void setModel(std::string modelName);
void initPhysics();
void deinitPhysics();
void getWorldTransform(btTransform& worldTrans) const;
void setWorldTransform(const btTransform &trans);
void parent(GEntity* parent);
protected:
unsigned long int m_id;
// Physics representation
btTransform m_trans;
btRigidBody* m_rigidBody;
// Graphics representation
Ogre::SceneNode* m_sceneNode;
Ogre::Entity* m_entity;
// Engine representation
GWorld* m_world;
GEntity* m_parent;
std::string m_name;
std::string m_model; // Used to find physics collision mesh
};
And here's the code calling setModel:
// Setup game world
GWorld* world = new GWorld(win);
GEntity* ent = world->createEntity();
ent->setModel(std::string("Cube.mesh"));

Answer 1

Your problem is that this line is constructing a nameless temporary GEntity inside the constructor body for a different GEntity. The temporary is then thrown away once the statement completes and no further initialization of the non-temporary GEntity is performed.
GEntity(world, idNum, btTransform::getIdentity());
If you want to share some initialization code between your two constructors you should create a member function that performs the required actions and call this function from both constructors. C++ doesn't (currently) allow you to delegate initialization from one constructor to a different constructor or call two constructors on the same object.

Answer 2

My best guess is that the problem is in GWorld::createEntity. If you're creating a local GEntity on the stack and returning a pointer to it, you'll see something like what you describe, as the GEntity is destroyed when GWorld::createEntity returns and the memory is reused for the temp string constructed to pass to setModel
Edit
I see you've added more code, including the definition of createEntity. That looks fine, but I would still suggest looking for some way in which the GEntity you're seeing the problem with gets deleted (and the memory reused for a string) before you call setModel.

Answer 3

One solution I have found is to use string.resize(n), which will resize the function. However, I do not know why this works, and I feel my problem is with my code since std::string is part of the standard C++ library.

Answer 4

I can't find the answer but I can make a suggestion that will help catch the problem:
Add assertions. A lot of assertions. Each one of those functions really need some assertions at least at their beginning. That will certainly help you catch wrong states early.
And by the way, you should use a constant reference as parameter of your setModel() function.

Answer 5

In C++ you can not call a constructor from within a constructor.

Answer 6

Try
GEntity::GEntity(GWorld* world, unsigned long int idNum) : GEntity(world, idNum, btTransform::getIdentity() {}