段錯誤複製構造函數爲字符串

Question

我得到一個段錯誤，我創建一個C++字符串與複製構造函數。我查看了一些類似的問題，但都是因爲傳入了一個錯誤的C++字符串對象。我只是傳入一個原始字符串，所以我不確定我的問題是什麼。我將粘貼相關的代碼片段（它來自多個不同的文件，因此可能看起來有點混亂）。段錯誤發生在Species類的默認構造函數的第4行。

Species::Species(string _type) { 
    program_length = 0; 
    cout << _type << " 1\n"; 
    cout << type << " 2\n"; 
    type = string(_type); 
} 

Grid::Grid(int _width, int _height) { 
    *wall = Species("wall"); 
    *empty = Species("empty"); 
    turn_number = 0; 
    width = _width; 
    height = _height; 
    for(int a= 0; a < 100; a++) 
     for(int b = 0; b< 100; b++) { 
      Creature empty_creature = Creature(*empty,a,b,NORTH,this); 
      (Grid::map)[a][b] = empty_creature; 
     } 
} 

int main() { 
    Grid world = Grid(8,8); 
} 

class Grid { 
protected: 
    Creature map[100][100]; 
    int width,height; 
    int turn_number; 
    Species *empty; 
    Species *wall; 
public: 
    Grid(); 
    Grid(int _width, int _height); 
    void addCreature(Species &_species, int x, int y, Direction orientation); 
    void addWall(int x, int y); 
    void takeTurn(); 
    void infect(int x, int y, Direction orientation, Species &_species); 
    void hop(int x, int y, Direction orientation); 
    bool ifWall(int x, int y, Direction orientation); 
    bool ifEnemy(int x, int y, Direction orientation, Species &_species); 
    bool ifEmpty(int x, int y, Direction orientation); 
    void print(); 
}; 

class Species { 
    protected: 
    int program_length; 
    string program[100]; 
    string type; 
    public: 
    species(string _type); 
    void addInstruction(string instruction); 
    bool isWall(); 
    bool isEmpty(); 
    bool isEnemy(Species _enemy); 
    string instructionAt(int index); 
    string getType(); 
}; 

這是我更新後的代碼，我從牆上刪除指針和空指針。現在我得到一個奇怪的錯誤（「錯誤：場牆面不網格成員」）：

Grid::Grid(int _width, int _height) { 
    (Grid::wall) = Species("wall"); 
     (Grid::empty) = Species("empty"); 
     cout << (*wall).getType() << "\n"; 
     turn_number = 0; 
     width = _width; 
     height = _height; 
     for(int a= 0; a < 100; a++) 
      for(int b = 0; b< 100; b++) { 
       Creature empty_creature = Creature(Grid::empty,a,b,NORTH,this); 
       (Grid::map)[a][b] = empty_creature; 
      } 
} 

class Grid { 
protected: 
    Creature map[100][100]; 
    int width,height; 
    int turn_number; 
    Species empty; 
    Species wall; 
public: 
    Grid(); 
    Grid(int _width, int _height); 
    void addCreature(Species &_species, int x, int y, Direction orientation); 
    void addWall(int x, int y); 
    void takeTurn(); 
    void infect(int x, int y, Direction orientation, Species &_species); 
    void hop(int x, int y, Direction orientation); 
    bool ifWall(int x, int y, Direction orientation); 
    bool ifEnemy(int x, int y, Direction orientation, Species &_species); 
    bool ifEmpty(int x, int y, Direction orientation); 
    void print(); 
}; 

Answer 1

問題的最可能的原因是，你去引用Species指針數據成員，而不初始化：

Grid::Grid(int _width, int _height) { 
    *wall = Species("wall"); // wall not initialized. What does it point to? 
    *empty = Species("empty"); // likewise for empty 

哪一個問題：你需要他們成爲指針嗎？ （提示：最有可能沒有）

當不使用指針，你可以很容易地初始化在構造函數的初始化列表中的數據成員：

Grid::Grid(int _width, int _height) 
: width(_width), height(_height), turn_number(0), wall("wall"), empty("empty") 
{ 
    .... 
}