SFML纹理持有人已删除，但仍在范围内

Question

So I'm new to SFML. I read a lot of post, but I really don't get it. I wrote an texture holder:

class tile_texture_holder {
private:
    sf::Texture tx;
public:
    tile_texture_holder(type a) {
        switch (a) {
        case type::desert:
            tx.loadFromFile("C:/Users/Andreas/source/repos/conquer/Media/desert.png");
            break;
        case type::grass:
            tx.loadFromFile("C:/Users/Andreas/source/repos/conquer/Media/grass.png");
            break;
        case type::mountain:
            tx.loadFromFile("C:/Users/Andreas/source/repos/conquer/Media/mountain.png");
            break;
        case type::water:
            tx.loadFromFile("C:/Users/Andreas/source/repos/conquer/Media/water.png");
            break;
        }
    }
    sf::Texture ret_texture() {
        return tx;
    }

    ~tile_texture_holder() {
        std::cout << "///////////////////////HOLDER DELETED!!!/////////////////////" << std::endl;
    }
};

And I tried to load a sprite with it in different ways....

For example:

tile_texture_holder t(type::desert);
        sf::Sprite s; 
        s.setTexture(t.ret_texture());

(in the same function, where I draw the sprite)

I always get the white box being drawn. And I really dont get why the texture_holder is getting deleted.

BTW type is an enum.

I hope somebody can help me solve my issue!

Answer 1

s.setTexture(t.ret_texture());

in the line above you have undefined behaviour.

ret_texture returns temporary texture (it is returned by value, so a copy is made), setTexture takes reference to it, then at the end of expression temporary texture is destroyed and you have dangling reference in s .

Why this happens? Because setTexture of Sprite only holds reference to texture, it doesn't copy it.

According to SFML Sprite reference :

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.

Solution: ret_texture should return texture by reference.

sf::Texture& ret_texture() {
    return tx;
}