Lost link with Sprite texture - c++

Question

I have this class to add Sprites to my game:
class Pickup {
public:
Pickup::Pickup()
{
Texture healthTexture;
healthTexture.loadFromFile("health.png");
m_Sprite.setTexture(healthTexture);
}
Sprite Pickup::getSprite()
{
return m_Sprite;
}
private:
Sprite m_Sprite;
};
I use Pickup nameSprite() to add another sprite to my game. But every time I do this (I tried with different images, I used if(!healthTexture.loadFromFile(..))to see if the problem is with the image) I only see a white rectangle instead of what I wanted, and nothing seems to be wrong. My question is: what is the cause for the link problem?

Answer 1

The SFML documentation states:
The texture argument refers to a texture that must exist as long as
the sprite uses it. Indeed, the sprite doesn't store its own copy of
the texture, but rather keeps a pointer to the one that you passed to
this function. If the source texture is destroyed and the sprite tries
to use it, the behaviour is undefined.
The Texture Object you create and load is local to your constructor and destroyed at its end, so once it is actually used later in your programs execution, the pointer/reference kept by the Sprite-Object is dangling.
To avoid the issue you could, for instance, save the Texture as an additional member in your Pickup class.
As pointed out by Lorence Hernandez in an insightful comment below, this would not, however, be an exceedingly good idea. Each instance of Pickup would hold its own texture instance, despite the textures being the same, wasting memory. Furthermore, Pickup could no longer use the default copy operations, as a copied Pickup's Sprite instance would subsequently refer to the texture instance in the original object.
A better approach would be to move the handling of this issue, i.e. management of texture instances and their lifetime, outside the Pickup class itself.
There is a multitude of possible solutions ranging from simple functions doing internal caching to more complicated resource manager classes.
The former could be as simple as the following snippet:
const Texture& load(const std::string &filename)
{
static std::map<std::string,std::unique_ptr<Texture>> textures;
auto &tex_ptr=textures[filename];
if(!tex_ptr)
tex_ptr=std::make_unique<Texture>(filename);
return *tex_ptr;
}
This simplistic version does, of course, have a minor "leak" as unused textures will never be freed during the programs execution.
Googling "texture manager sfml" will yield many examples and tutorials regarding the latter, for instance this rather old unofficial one in SFML's github. It manages sf::Image, not sf::Texture, but the same general ideas apply.