C++ Vector Size is Zero - c++

Question

I am trying to create a function that renders everything in a vector of displayobject objects (on another thread). I am using SDL thread.
Here is the displayobject.h:
class DisplayObject
{
protected:
int width;
int height;
int x;
int y;
SDL_Texture* texture;
SDL_Renderer* renderer;
public:
~DisplayObject();
int getX();
void setX(int x);
int getY();
void setY(int y);
int getWidth();
void setWidth(int width);
int getHeight();
void setHeight(int height);
SDL_Texture* getTexture();
SDL_Renderer* getRenderer();
};
In graphics.h I have these variables:
std::vector<DisplayObject> imgArr;
SDL_Thread* renderThread;
static int renderLoop(void* vectorPointer);
This code is in the graphics constructor:
TextLabel textLabel(graphics->getRenderer(), 300, 80, "Hallo Welt", 50, Color(255, 0, 255), "Xenotron.ttf");
//TextLabel inherits from DisplayObject
imgArr.push_back(textLabel);
renderThread = SDL_CreateThread(Graphics::renderLoop, "renderLoop", &imgArr);
This is the render loop function:
int Graphics::renderLoop(void* param)
{
int counter = 0;
bool rendering = true;
std::vector<DisplayObject>* imgArr = (std::vector<DisplayObject>*)param;
while (rendering)
{
cout << imgArr->size() << endl;
counter++;
if (counter > 600)
{
rendering = false;
}
SDL_Delay(16);
}
return 0;
}
The problem is that it only prints 0's in the console. Why does it do that? It is supposed to write 1 since I pushed on object into it.

Answer 1

When you insert a TextLabel into std::vector<DisplayObject>, what is stored in the vector is not your original TextLabel object, but a DisplayObject copy-constructed from the TextLabel. What you want to do is create your TextLabels with new, store pointers to them, and call delete when you no longer need them.
The best solution would be to use boost::ptr_vector<DisplayObject> instead - it will automatically call delete when you erase objects from it.
http://www.boost.org/doc/libs/1_57_0/libs/ptr_container/doc/ptr_container.html
If you can't use Boost, but can use C++11, you can use std::vector<std::unique_ptr<DisplayObject>>.