Is the cartTexture member actually initialized correctly?

Question

Problem Description:

I am working on making a Cart class that has a sf::Sprite(cartSprite) in each instance. However, the static sf::Texture(cartTexture) from which carts are generated is shared between all Cart objects. On construction of a Cart, the sprite is loaded from the texture.

According to the documentation, the sf::Texture has a default constructor that:

Creates an empty texture.

However, when I compile the code below, that declares, but does not define, the sf::Texture, I get linker errors:

/tmp/cclJ5hJp.o: In function `Cart::Cart(sf::Vector2<float> const&, sf::Color, float)':
main.cpp:(.text._ZN4CartC2ERKN2sf7Vector2IfEENS0_5ColorEf[_ZN4CartC5ERKN2sf7Vector2IfEENS0_5ColorEf]+0x46): undefined reference to `Cart::cartTexture'
main.cpp:(.text._ZN4CartC2ERKN2sf7Vector2IfEENS0_5ColorEf[_ZN4CartC5ERKN2sf7Vector2IfEENS0_5ColorEf]+0x87): undefined reference to `Cart::cartTexture'
main.cpp:(.text._ZN4CartC2ERKN2sf7Vector2IfEENS0_5ColorEf[_ZN4CartC5ERKN2sf7Vector2IfEENS0_5ColorEf]+0x9b): undefined reference to `Cart::cartTexture'
main.cpp:(.text._ZN4CartC2ERKN2sf7Vector2IfEENS0_5ColorEf[_ZN4CartC5ERKN2sf7Vector2IfEENS0_5ColorEf]+0xb6): undefined reference to `Cart::cartTexture'
collect2: error: ld returned 1 exit status

Does this mean that I should initialize (define) cartTexture? If so, how do I do that at compile-time when the only constructors for sf::Texture are "copy from another sf::Texture" and the one mentioned above? I can't use a function call to load an image into it, right?

Compile the code with: g++ main.cpp -Wall -Wextra -Werror -std=c++11 -lsfml-graphics -lsfml-window -lsfml-system -o exec

Code:

main.cpp:

#include <SFML/Graphics.hpp>
#include <string>
#include <iostream>
#include <mutex>

class Cart : public sf::Drawable {

    public:
        // Constructor- create with position, orientation, and color.
        Cart(const sf::Vector2f& cartPos_, sf::Color cartColor_, float cartAngle_) {

            if (!cartTexture.loadFromFile(textureLoc)) {
                std::cout << "File is nonexistent." << std::endl;
            } else {
                cartTexture.setSmooth(true);
                cartTexture.setRepeated(false);
            }   

            cartSprite.setTexture(cartTexture);

            cartSprite.setPosition(cartPos_);
            cartSprite.setRotation(cartAngle_);
            cartSprite.setColor(cartColor_);
        }

    private:
        void draw(sf::RenderTarget& target, sf::RenderStates states) const {
            target.draw(cartSprite, states);
            return;
        }

        static sf::Texture cartTexture;
        static const std::string textureLoc;

        sf::Sprite cartSprite;
};

const std::string Cart::textureLoc = "cart-empty.png";

int main() {

    Cart testCart(sf::Vector2f(), sf::Color(200,200,200), 0);

    return 0;
}

[From documentation](http://sfml-dev.org/tutorials/2.0/start-linux.php): *"If you installed SFML to a non-standard path, you'll need to tell the linker where to find the SFML libraries (.so files):"* So maybe add `-L/lib` — clcto, Aug 15 '14 at 22:19
Nope, it's in the right spot- I have compiled other programs with this set of linker options effectively. Also, it would be a bit strange if the `sf::Vector2f`s and the `sf::Color`s somehow worked fine, but the `sf::Texture` did not work, when the library path was messed up. The issue has to do with initialization of variables, I believe. — Blue Ice, Aug 15 '14 at 22:24
Oh it is `static`. You need to initialize it like you did `textureLoc`. Add `sf::Texture Cart::cartTexture;` after the initialization of `Cart::textureLoc` — clcto, Aug 15 '14 at 22:28

score 2 · Accepted Answer · answered Aug 15 '14 at 22:33

2

static class member variables have to be initialized/defined outside of the class definition. You do this for textureLoc but not cartTexture. Before main() add:

sf::Texture Cart::cartTexture;

answered Aug 15 '14 at 22:33

clcto

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Thanks- that did it. Sort of backwards, but it worked, and I'll keep it in mind for next time. – Blue Ice Aug 15 '14 at 22:34
See here for more information: http://stackoverflow.com/questions/11178434/static-variable-in-the-class-declaration-or-definition – clcto Aug 15 '14 at 22:35

Is the cartTexture member actually initialized correctly?

Problem Description:

Code:

1 Answers1