C++ 錯誤：LINK2005

Question

1. 問題描述
   common.h定義所有的類型別名和結構體聲明，被mass_diffusion.h和 heat_conduction.h所引用，mass_diffusion.h和heat_conduction.h被man.cpp所引用，然後編譯成功，連結的時候報錯LINK2005。我已經使用了#ifndef ... #define ... #endif這種防禦性語法；每個檔案暴露在外面的只有一個init函數，檔案內部雖然都有重名函數，但是他們沒有對外暴露為什麼還會報錯？

2. 錯誤訊息
   visual studio 2017 編譯C++ 錯報：LNK2005 mass_diffusion.obj中的"void __cdecl compute(class std::vector<struct user ,structuser # class std::allocator<struct user > > ,class std::vector<struct item ,class std::allocator<struct item > > ) "已經在heat_conduction.obj 中定義。

3. #相關程式碼

   //common.h
   #ifndef _COMMON_H
   #define _COMMON_H
   ...
   struct user;
   struct item;
   struct relation;
   ...
   typedef unsigned int _container_number_;
   typedef unsigned int _value_number_;
   ...
   typedef std::vector<user*> user_container;##typedefd:: vector<item*> item_container;
   #endif // !_COMMON_H
   ...
   
   //mass_diffusion.h##include "common.h"
   extern void init_md(user_container
   , item_container);void compute(user_container
   _ulist, item_container _ilist);...
   
   //mass_diffusion. cpp#include "mass_diffusion.h"
   void init_md(user_container
   _ulist, item_container _ilist){...};void compute(user_container
   _ilist){...};void compute(user_container _ulist,
   _ulist,
   item_container _ilist) {...};...
   
   //heat_conduction.h#include "common.h"
   extern void init_hc(user_container _ulist, item_container _ilist);
   void compute(user_container
   _ulist, item_container _ilist);...
   
   //heat_conduction.cppinclude "heat_conduction.h"
   void init_hc(user_container _ulist, item_container _ilist){...};
   void compute(user_container
   _ulist){...};void compute(user_container _ulist, it#container,# # _ilist) {...};
   ...
   

   //main.cpp

##include "mass_diffusion.h"####include "heat_conduction.h"# ## ### ###

Answer 1

本來就會報錯，你各個模組都連結到同一個檔案裡，連結器一看那麼多符號都一個名字自然就gg了，.h裡面暴露什麼連結器不會管的，解決方法是各個模組獨立編譯成so或dll，然後再調用，或用命名空間