在單獨的頭文件中的C++結構

Question

我試圖組織我的項目，所以我想我會包括我的全局變量，#includes和結構定義在global.h頭文件中。然而，我無法完全理解這個概念，而構建過程中的錯誤似乎證明了這一點。當我嘗試在logic.h中訪問我的global.h時，會發生什麼情況。

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); 

當我嘗試構建它，這是我得到的錯誤：

||=== 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)) ===| 

我不知道我錯過了什麼。感謝您的任何建議！

Answer 1

當你include "global.h"，的第一東西它說一個是include "logic.h"，因此處理器打開這個文件，找到一個include "global.h"，這確實是因爲包括後衛的什麼都沒有，然後發現void initCharacter(Character &newCharacter,和迷糊，因爲它不還不知道Character是什麼。然後它從那個包含中返回，然後是enum directions，然後最後是從而struct Character，所以然後它知道什麼是Character，太遲了。

一般來說，儘量確保只包含一種方法。確保logic包含global，或者global包含logic，但不是兩者都包含。或者，如果你真的懶惰，有時候會迴避這個問題：把函數和類定義放在包含之前，儘可能頻繁。然後global會告訴編譯器，class Character存在，那麼當它包含logic.h時，它不會有問題。

#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 
{ 
    ...