C++：也许你知道这个陷阱？
我正在开发一款游戏。我有一个带有两个变量的标头 GameSystem （只是游戏循环之类的方法，没有类）：int mouseX 和 int mouseY。这些在我的游戏循环中更新。现在我想从 Game.cpp 文件（由头文件和源文件构建的类）访问它们。因此，我在 Game.h 中#include "GameSystem.h"。执行此操作后，我收到很多编译错误。当我删除包含内容时，他当然会说：
Game.cpp:33: 错误：“mouseX”未在此范围内声明Game.cpp:34: 错误：“mouseY”未在此范围内声明
我想要访问 mouseX 和 mouseY 的位置。
我的所有 .h 文件都有由 Eclipse 生成的标头防护。
我正在使用 SDL，如果删除想要访问变量的行，所有内容都会完美编译并运行 (*)。
我希望你能帮助我...
这是我 #include "GameSystem.h" 时的错误日志（他引用的所有代码都有效，如 (*) 所解释的那样）：
In file included from ../trunk/source/domein/Game.h:14,
from ../trunk/source/domein/Game.cpp:8:
../trunk/source/domein/GameSystem.h:30: error: expected constructor, destructor, or type conversion before ‘*’ token
../trunk/source/domein/GameSystem.h:46: error: variable or field ‘InitGame’ declared void
../trunk/source/domein/GameSystem.h:46: error: ‘Game’ was not declared in this scope
../trunk/source/domein/GameSystem.h:46: error: ‘g’ was not declared in this scope
../trunk/source/domein/GameSystem.h:46: error: expected primary-expression before ‘char’
../trunk/source/domein/GameSystem.h:46: error: expected primary-expression before ‘bool’
../trunk/source/domein/FPS.h:46: warning: ‘void FPS_SleepMilliseconds(int)’ defined but not used
这是尝试访问两个变量的代码：
SDL_Rect pointer;
pointer.x = mouseX;
pointer.y = mouseY;
pointer.w = 3;
pointer.h = 3;
SDL_FillRect(buffer, &pointer, 0xFF0000);
I'm developing a game. I have a header GameSystem (just methods like the game loop, no class) with two variables:int mouseX and int mouseY. These are updated in my game loop. Now I want to access them from Game.cpp file (a class built by a header-file and the source-file). So, I #include "GameSystem.h" in Game.h. After doing this I get a lot of compile errors. When I remove the include he says of course:
Game.cpp:33: error: ‘mouseX’ was not declared in this scopeGame.cpp:34: error: ‘mouseY’ was not declared in this scope
Where I want to access mouseX and mouseY.
All my .h files have Header Guards, generated by Eclipse.
I'm using SDL and if I remove the lines that wants to access the variables, everything compiles and run perfectly (*).
I hope you can help me...
This is the error-log when I #include "GameSystem.h" (All the code he is refering to works, like explained by the (*)):
In file included from ../trunk/source/domein/Game.h:14,
from ../trunk/source/domein/Game.cpp:8:
../trunk/source/domein/GameSystem.h:30: error: expected constructor, destructor, or type conversion before ‘*’ token
../trunk/source/domein/GameSystem.h:46: error: variable or field ‘InitGame’ declared void
../trunk/source/domein/GameSystem.h:46: error: ‘Game’ was not declared in this scope
../trunk/source/domein/GameSystem.h:46: error: ‘g’ was not declared in this scope
../trunk/source/domein/GameSystem.h:46: error: expected primary-expression before ‘char’
../trunk/source/domein/GameSystem.h:46: error: expected primary-expression before ‘bool’
../trunk/source/domein/FPS.h:46: warning: ‘void FPS_SleepMilliseconds(int)’ defined but not used
This is the code which try to access the two variables:
SDL_Rect pointer;
pointer.x = mouseX;
pointer.y = mouseY;
pointer.w = 3;
pointer.h = 3;
SDL_FillRect(buffer, &pointer, 0xFF0000);
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在您的
GameSystem标头中，不要将这些变量定义为：相反，您应该声明它们：
然后在您的 .cpp 文件之一中定义它们：
在头文件中定义它们的问题是编译器将尝试在包含标头的每个 .cpp 中实例化它们。
In your
GameSystemheader, don't define those variables as:instead, you should declare them:
Then in one of your .cpp files you define them:
The problem with defining them in a header file is that the compiler will try to instantiate them in every single .cpp where you include the header.