爲什麼這個C++（cocos2d，box2d）示例給出一個指針而不是一個值？

Question

我創建這個結構：

struct MyBodyData 
{ 
    int someNumber; 
}; 

，然後創建一個新的機構：

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); 

，然後試圖訪問someNumber這裏：

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); 
    } 
} 

它顯示someNumber作爲一個內存地址長6-7位，而不是值「4」。

我錯過了什麼？

Answer 1

body1->SetUserData(&bodyData); 

你定身的數據是指針bodyData的地址。你不想要那個，你想把它設置爲bodyData。所以：

body1->SetUserData(bodyData);