Question

I have a memory issue with a class of mine. The issue occurs when I create an object in a member function of a class. It is about the class below. I removed the member functions because they aren’t necessary:

class User
{
private:
    bool locked;
    bool active;

    std::vector<City> * userCitys;
    UserData userData;
    Credentials credentials;

The problem occurs when I call this function:

int User::addCity(CityData cityData) 
{
    lockUserObject(); //Everything is fine here

    City cityToAdd; //When this object is created, the memory of userCitys will get overridden
    cityToAdd.activate();
    userCitys->push_back(cityToAdd);
    int cityID = userCitys->size() - 1;

    userCitys->at(cityID).editCityData(cityData);

    unlockUserObject();
    return cityID;
}

In the first place I created userCitys on the stack. For test purpose I placed it on the Heap. The address of userCitys get overridden by some data. I can’t find the problem. the City is just a basic class:

Part of the header:

class City
{
private:
    bool active;
    Supplies supplies;
    std::vector<Building> buildings;
    std::vector<Company> companies;
    std::vector<Share> shares;
    std::vector<Troop> troops;
    CityData cityData;

Constructor:

City::City()
{
    active = false; 
}

How is it possible that userCitys get overridden? This all happens on a single Thread so that can’t be a problem. I tried a lot of thing, but I can’t get it to work. What is the best approach to find the problem?

Edit:
Lock function:

void User::lockUserObject()
{
    for( int i = 0; locked ; i++)
    {
        crossSleep(Settings::userLockSleepInterval);

        if( i >= Settings::userLockMaxTimes )
            Error::addError("User lock is over userLockMaxTimes",2);
    }

    locked = true;
}

I call the code here (Test function):

City * addCity(User * user)
{
    Location location;
    location.x = 0;
    location.y = 1;

    CityData citydata;
    citydata.location = location;
    citydata.villagers = 0;
    citydata.cityName = "test city";

    int cityID = user->addCity(citydata); //addCity is called here
    City * city = user->cityAction(cityID);;

    if( city == NULL)
        Error::addError("Could not create a city",2);

    return city;
}

The add user (Test code):

User * addUser()
{
    UserData test;
    test.name = "testtest";
    Credentials testc("testtest",3);

    //Create object user
    int userID = UserControle::addUser(test,testc);
    User * user = UserControle::UserAction(userID);

    if( user == NULL)
        Error::addError("Could not create a user",2);

    return user;
}

My test function:

void testCode()
{
    User * user = addUser();
    City * city = addCity(user);
}

This function in called in main:

int main()
{
    testCode();
    return 0;
}

Here are UserAction and addUser in UserControle:

int UserControle::addUser(UserData userdata, Credentials credentials)
{
    int insertID = -1;
    for( int i = 0; i < (int)UserControle::users.size(); i++)
    {
        if( !UserControle::users.at(i).isActive() )
        {
            insertID = i;
            break;
        }   
    }

    User userToInsert(userdata,credentials);

    if( insertID != -1 )
    {
        UserControle::users.insert( UserControle::users.begin() + insertID,userToInsert);
        return insertID;
    }
    else
    {
        UserControle::users.push_back(userToInsert);
        return UserControle::users.size() - 1;
    }
}

User* UserControle::UserAction(int userID) //check all indexes if greater then 0!
{
    if( (int)UserControle::users.size() <= userID )
    {
        Error::addError("UserAction is out of range",3);
        return NULL;
    }

    if( !UserControle::users.at(userID).isActive())
    {
        Error::addError("UserAction, the user is not active.",3);
        return NULL;
    }

    return &UserControle::users[userID];
}

Answer 1

There’s a few things you could try:

• Remove code until the fault goes away. In other words, distill a minimal example from your code. I guess you’ll then see the error yourself, otherwise post that small example program here and others will.
• Don’t use raw pointers. The question with those is always who owns what they point to. Use smart pointers instead, e.g. unique_ptr (C++11) or auto_ptr (C++98) for exclusive ownership.
• If you have pointer members like “userCities”, you need to think about what happens when copying instances of that class (you already wrote a proper destructor, or?). So, either prevent copying (make copy-constructor and assignment operator private and without implementing it) or implement them in a way that the vectors are properly cloned and not shared between different instances.
• Don’t use C-style casts. If those are necessary to get anything through the compiler, the code is probably broken.