为什么这个 C++ (cocos2d, box2d) 示例给出一个指针而不是一个值？

Question

我创建了这个结构：

struct MyBodyData
{
    int someNumber;
};

然后创建了一个新的主体：

b2BodyDef bodyDef;
bodyDef.type = b2_dynamicBody;
bodyDef.position.Set(0.0f, -10.0f);
b2Body* body1 = world->CreateBody(&bodyDef);
MyBodyData *bodyData = new MyBodyData();
bodyData->someNumber = 4;
body1->SetUserData(&bodyData);

b2PolygonShape dynamicBox;
dynamicBox.SetAsBox(.5f, .5f);//These are mid points for our 1m box
b2FixtureDef fixtureDef;
fixtureDef.shape = &dynamicBox; 
fixtureDef.density = 1.0f;
fixtureDef.friction = 0.3f;
body1->CreateFixture(&fixtureDef);

然后尝试在此处访问 someNumber：

for (b2Body* b = world->GetBodyList(); b; b = b->GetNext())
{
    CCLOG(@"Hello One");
    MyBodyData* data = (MyBodyData*)b->GetUserData();
    if (data!=0 && data->someNumber != 0)
    {
        int temp;
        temp = data->someNumber;
        CCLOG(@"Hello Again! %d",temp);
    }
}

它将 someNumber 显示为 6-7 位长的内存地址，而不是值“4”。

我缺少什么？

Answer 1

body1->SetUserData(&bodyData);

您将正文数据设置为指针的地址 bodyData。您不希望这样，您希望将其设置为 bodyData。所以：

body1->SetUserData(bodyData);