在单独的头文件中的C++结构

Question

我试图组织我的项目，所以我想我会包括我的全局变量，#includes和结构定义在global.h头文件中。然而，我无法完全理解这个概念，而构建过程中的错误似乎证明了这一点。当我尝试在logic.h中访问我的global.h时，会发生什么情况。

global.h：

#ifndef GLOBAL_H 
#define GLOBAL_H 
#include "logic.h" 
#include <SDL.h> 
#include <iostream> 
#include <string> 
#include "graphics.h" 

//Global variables and structs 
enum directions 
{ 
    D_UP, 
    D_LEFT, 
    D_DOWN, 
    D_RIGHT, 
    D_TOTAL 
}; 

struct Character 
{ 
    float health; 
    float x; 
    float y; 
    float velocity; 
    bool collision[D_TOTAL]; 
    directions direction; 
    SDL_Rect animation; 
    SDL_Rect sprite; 
}; 

const int windowWidth = 800; 
const int windowHeight = 600; 
const int frameWidth = 64; 
const int frameHeight = 64; 
#endif // GLOBAL_H 

logic.h：

#include "global.h" 
//Header for gamelogic functions 

//Initialization of all variables for a new character 
void initCharacter(Character &newCharacter, float x, float y, directions startingDirection); 

当我尝试构建它，这是我得到的错误：

||=== Build: Debug in GameProject0.2 (compiler: GNU GCC Compiler) ===| 
C:\Users\Rafał\Documents\GameProject0.2\GameProject0.2\logic.h|5|error: variable or field 'initCharacter' declared void| 
C:\Users\Rafał\Documents\GameProject0.2\GameProject0.2\logic.h|5|error: 'Character' was not declared in this scope| 
C:\Users\Rafał\Documents\GameProject0.2\GameProject0.2\logic.h|5|error: 'newCharacter' was not declared in this scope| 
C:\Users\Rafał\Documents\GameProject0.2\GameProject0.2\logic.h|5|error: expected primary-expression before 'float'| 
C:\Users\Rafał\Documents\GameProject0.2\GameProject0.2\logic.h|5|error: expected primary-expression before 'float'| 
C:\Users\Rafał\Documents\GameProject0.2\GameProject0.2\logic.h|5|error: 'directions' was not declared in this scope| 
||=== Build failed: 6 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===| 

我不知道我错过了什么。感谢您的任何建议！

Answer 1

当你include "global.h"，的第一东西它说一个是include "logic.h"，因此处理器打开这个文件，找到一个include "global.h"，这确实是因为包括后卫的什么都没有，然后发现void initCharacter(Character &newCharacter,和迷糊，因为它不还不知道Character是什么。然后它从那个包含中返回，然后是enum directions，然后最后是从而struct Character，所以然后它知道什么是Character，太迟了。

一般来说，尽量确保只包含一种方法。确保logic包含global，或者global包含logic，但不是两者都包含。或者，如果你真的懒惰，有时候会回避这个问题：把函数和类定义放在包含之前，尽可能频繁。然后global会告诉编译器，class Character存在，那么当它包含logic.h时，它不会有问题。

#ifndef GLOBAL_H 
#define GLOBAL_H 

enum directions; 
struct Character; //If you're really lazy, this usually works 

#include "logic.h" 
#include <SDL.h> 
#include <iostream> 
#include <string> 
#include "graphics.h" 

//Global variables and structs 
enum directions 
{ 
    D_UP, 
    D_LEFT, 
    D_DOWN, 
    D_RIGHT, 
    D_TOTAL 
}; 

struct Character 
{ 
    ...