C ++类前向声明 [英] C++ class forward declaration

问题描述

当我尝试编译这个代码，我得到：

  52 C：\Dev-Cpp \Projektyyy \ strategy \Tiles.h无效使用未定义类型struct tile_tree_apple 
 46 C：\Dev-Cpp \Projektyyy \strategy\ Tiles.h`struct tile_tree_apple'的向前声明
  

我的代码的某些部分：

  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;}; 
}; 
  

我真的不知道该怎么办，我搜索的解决方案，但我couldnt找不到任何类似于我问题...事实上，我有更多的课程与父瓦片，它是确定之前...
Thanx任何帮助。

编辑： / p>

我决定将所有返回的类型改为指针，以避免内存泄漏，但现在我有：

  27 C：\Dev-Cpp \Projektyyy \strategy\Tiles.h ISO C ++禁止声明没有类型
的`tile'声明27 C：\Dev-Cpp\\ \\ Projektyyy \strategy\Tiles.h expected`;'beforetick
  

基本类，一切都是确定...每个函数在瓦片类返回*瓦有这个错误...

一些代码：

  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（）{}; 
}; 
  

解决方案

为了 以编译， T 必须是完整类型。在你的情况下不是。尝试将函数的内联定义移动到单独的源文件，或至少移动它们的类定义。

像：

  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（）{...} 
  

When I try to compile this code i get:

52 C:\Dev-Cpp\Projektyyy\strategy\Tiles.h invalid use of undefined type `struct tile_tree_apple' 
46 C:\Dev-Cpp\Projektyyy\strategy\Tiles.h forward declaration of `struct tile_tree_apple' 

some part of my code:

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;};       
};

I dont really know what to do, I searched for the solution but I couldnt find anything simmilar to my problem... Actually, i have more classes with parent "tile" and It was ok before... Thanx for any help.

EDIT:

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

27 C:\Dev-Cpp\Projektyyy\strategy\Tiles.h ISO C++ forbids declaration of `tile' with no type 
27 C:\Dev-Cpp\Projektyyy\strategy\Tiles.h expected `;' before "tick"

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

Some code:

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() {};
};

解决方案

In order for new T to compile, T must be a complete type. In your case it isn't. Try moving the inline definitions of your functions to a separate source file, or at least move them afte r the class definitions.

Something like:

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() {...}

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