Box2d функция SetUserData()

#include <SFML/Graphics.hpp>
#include <Box2D/Box2D.h>
 
using namespace sf;
 
const float SCALE = 30.f;
const float DEG = 57.29577f;
 
b2Vec2 Gravity(0.f, 9.8f);
b2World World(Gravity);
 
int main()
{
    RenderWindow window(sf::VideoMode(800, 600), "BlobVol!");
    window.setFramerateLimit(60);
 
    Texture t1, t2;
 
    t1.loadFromFile("C:\\Users\\sssam\\source\\repos\\Project3\\images\\background.png");
    t2.loadFromFile("C:\\Users\\sssam\\source\\repos\\Project3\\images\\ball.png");
 
    Sprite sBackground(t1), sBall(t2);
    sBall.setOrigin(32, 32);
 
    b2PolygonShape shape;
    shape.SetAsBox(30 / SCALE, 30 / SCALE);
    b2BodyDef bdef;
    bdef.type = b2_dynamicBody;
    bdef.position.Set(5, 1);
    b2CircleShape circle;
    circle.m_radius = 32 / SCALE;
    b2Body *b = World.CreateBody(&bdef);
    b2FixtureDef fdef;
    fdef.shape = &circle;
    fdef.restitution = 0.95;
    fdef.density = 0.2;
    b->CreateFixture(&fdef);
 
    b->SetUserData("ball");
 
    while (window.isOpen())
    {
        sf::Event event;
        while (window.pollEvent(event))
        {
            if (event.type == sf::Event::Closed)
                window.close();
        }
 
        World.Step(1 / 60.f, 8, 3);
 
        window.draw(sBackground);
        for (b2Body* it = World.GetBodyList(); it != 0; it = it->GetNext())
        {
            b2Vec2 pos = it->GetPosition();
            float angle = it->GetAngle();
 
            if (it->GetUserData() == "ball")
            {
                sBall.setPosition(pos.x*SCALE, pos.y*SCALE);
                sBall.setRotation(angle*DEG);
                window.draw(sBall);
            }
 
        }
        window.display();
    }
 
    return 0;
}

char ball_str[] = "ball";
//...
b->SetUserData(ball_str);