問題描述

當(dāng)我嘗試編譯這段代碼時，我得到:

When I try to compile this code, I get:

52 C:Dev-CppProjektyyystrategyTiles.h invalid use of undefined type `struct tile_tree_apple' 
46 C:Dev-CppProjektyyystrategyTiles.h forward declaration of `struct tile_tree_apple' 

我的部分代碼:

class tile_tree_apple;

class tile_tree : public tile
{
      public:
          tile onDestroy() {return *new tile_grass;};
          tile tick() {if (rand()%20==0) return *new tile_tree_apple;};
          void onCreate() {health=rand()%5+4; type=TILET_TREE;};        
};

class tile_tree_apple : public tile
{
      public:
          tile onDestroy() {return *new tile_grass;};
          tile tick() {if (rand()%20==0) return *new tile_tree;};
          void onCreate() {health=rand()%5+4; type=TILET_TREE_APPLE;}; 
          tile onUse() {return *new tile_tree;};       
};

我真的不知道該怎么辦，我搜索了解決方案，但找不到任何與我的問題類似的東西...實際上，我有更多與父級tile"相關(guān)的課程.之前還可以...

I dont really know what to do, I searched for the solution but I couldn't find anything simmilar to my problem... Actually, I have more classes with parent "tile" and It was ok before...

我決定將所有返回的類型更改為指針以避免內(nèi)存泄漏，但現(xiàn)在我得到了:

I decided to change all returned types to pointers to avoid memory leaks, but now I got:

27 C:Dev-CppProjektyyystrategyTiles.h ISO C++ forbids declaration of `tile' with no type 
27 C:Dev-CppProjektyyystrategyTiles.h expected `;' before "tick"

僅在基類中，其他一切正常... tile 類中返回 *tile 的每個函數(shù)都有此錯誤...

Its only in base class, everything else is ok... Every function in tile class which return *tile has this error...

一些代碼:

class tile
{
      public:
          double health;
          tile_type type;
          *tile takeDamage(int ammount) {return this;};
          *tile onDestroy() {return this;};
          *tile onUse() {return this;};
          *tile tick() {return this};
          virtual void onCreate() {};
};

推薦答案

new T 要編譯，T 必須是完整類型.在您的情況下，當(dāng)您在 tile_tree::tick 的定義中說 new tile_tree_apple 時，tile_tree_apple 是不完整的(它已被前向聲明，但是它的定義稍后在您的文件中).嘗試將函數(shù)的內(nèi)聯(lián)定義移動到單獨的源文件中，或者至少將它們移動到類定義之后.

In order for new T to compile, T must be a complete type. In your case, when you say new tile_tree_apple inside the definition of tile_tree::tick, tile_tree_apple is incomplete (it has been forward declared, but its definition is later in your file). Try moving the inline definitions of your functions to a separate source file, or at least move them after the class definitions.

類似于:

class A
{
    void f1();
    void f2();
};
class B
{
   void f3();
   void f4();
};

inline void A::f1() {...}
inline void A::f2() {...}
inline void B::f3() {...}
inline void B::f4() {...}

當(dāng)您以這種方式編寫代碼時，這些方法中對 A 和 B 的所有引用都保證引用完整類型，因為不再有前向引用！

When you write your code this way, all references to A and B in these methods are guaranteed to refer to complete types, since there are no more forward references!

這篇關(guān)于C++ 類前向聲明的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網(wǎng)！