指針引用問題

我有一個函數void MOVE_TO(Square **sendingSquare, Square **receivingSquare)，其中Square是一個類：指針引用問題

class Square; 
class Entity 
{  
public: 
    Square *currentSq; 
};// Just a data type--pretend it's your favorite class. 
class Square 
{ 
public: 
    Entity *occupant; 
}; 

void MOVE_TO(Square **sendingSquare, Square **receivingSquare) 
{ 
    Entity *movingOccupant = (*sendingSquare)->occupant; 
    (*receivingSquare)->occupant = movingOccupant; 
    movingOccupant->currentSq = *receivingSquare; 
    (*sendingSquare)->occupant = NULL; 
}

問題是，當MOVE_TO(...)的回報，無論是正方形，然後在接收方指出，這應該是乘客感動已經消失了。理念的/建議嗎？我的代碼幾乎堅持到我可以解決這個問題。如果我在提出任何建議之前找出問題，我會回來回答我自己的問題。

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2012-12-05 Ian

爲什麼你使用'廣場**'指針而不是簡單的'廣場*'指針作爲'MOVE_TO'參數這是完全不清楚，但如果正確完成，那仍然可以工作。它應該以目前的形式運作。我在MOVE_TO裏面看不到任何會產生你描述的奇怪行爲的東西。無論如何，呼叫MOVE_TO的地方在哪裏？你怎麼稱呼它？ – AnT

我會改變'MOVE_TO'上的套管。它看起來像一個宏，因爲宏通常都是大寫的，所以它們以宏的形式出現。 – chris

@AndreyT我會嘗試使用單指針，看看有什麼。 – Ian

我假設你想要將實體的實例從sendingSquare移動到receivingSquare，並調整移動的實體的currentSq，使其返回到receivingSquare。

，如果是這樣的話，下面的代碼將做到這一點：

#include <iostream> 
using namespace std; 

class Square; 
class Entity 
{  
public: 
    Square *currentSq; 
    Entity(): currentSq(NULL){}//set currentSq to NULL using constructor initialization list 
}; 

class Square 
{ 
public: 
    Entity *occupant; 
    Square(): occupant(NULL){}//set occupant to NULL using constructor initialization list 
}; 

//MOVE_TO with single '*' 
void MOVE_TO(Square *sendingSquare, Square *receivingSquare) 
{ 
    Entity *movingOccupant = sendingSquare->occupant; 
    receivingSquare->occupant = movingOccupant; 
    movingOccupant->currentSq = receivingSquare; 
    sendingSquare->occupant = NULL; 
} 

int main(int argc, char** argv) { 
    //create instances 
    Square *sendingSquare = new Square(), *receivingSquare = new Square(); 
    Entity *entity = new Entity(); 

    //set up instances accordingly 
    sendingSquare->occupant = entity; 
    entity->currentSq = sendingSquare; 

    //print instances address before MOVE_TO invoked 
    //we know that receivingSquare.occupant is NULL, printing receivingSquare.occpuant.currentSq is commented 
    cout << "sendingSquare: "<< sendingSquare 
     << ", sendingSquare.occupant: " << sendingSquare->occupant 
     << ", sendingSquare.occupant.currentSq: " << sendingSquare->occupant->currentSq 
     << ", receivingSquare: " <<receivingSquare 
     << ", receivingSquare.occupant: " << receivingSquare->occupant 
     //<< ", sendingSquare.occupant.currentSq: " << receivingSquare.occupant->currentSq 
     << endl; 

    MOVE_TO(sendingSquare,receivingSquare); 

    //print instances address afer MOVE_TO invoked 
    //we know that sendingSquare.occupant is NULL, printing sendingSquare.occpuant.currentSq is commented 
    cout << "sendingSquare: "<< sendingSquare 
     << ", sendingSquare.occupant: " << sendingSquare->occupant 
     //<< ", sendingSquare.occupant.currentSq: " << sendingSquare.occupant->currentSq 
     << ", receivingSquare: " << receivingSquare 
     << ", receivingSquare.occupant: " << receivingSquare->occupant 
     << ", receivingSquare.occupant.currentSq: " << receivingSquare->occupant->currentSq 
     << endl; 

    //commenting instance deletion. The program is ended anyway 
    //delete entity,sendingSquare,receivingSquare; 
    return 0; 
}

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2012-12-05 06:35:34 riza

指針引用問題

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