錯誤LNK2005：構造函數已定義

Question

我有一個名爲UIHandling.h的頭文件中稱爲UIHandling的類。 在班上名列前茅我確信使用方法：

#ifndef _UIH_ 
#define _UIH_ 

當然，結束了與#endif

文件這個頭文件由構造函數的所有實現。 我已經包括在我的計劃，但由於某種原因，這個類在許多文件，我得到以下編譯器錯誤：

1>CompaniesMap.obj : error LNK2005: "public: __thiscall UIHandling::UIHandling(enum eType)" (??0UIHandling@@QAE@W4eType@@@Z) already defined in Bond.obj 
1>CompaniesMap.obj : error LNK2005: "public: __thiscall UIHandling::UIHandling(void)" (??0UIHandling@@QAE@XZ) already defined in Bond.obj 
1>Company.obj : error LNK2005: "public: __thiscall UIHandling::UIHandling(enum eType)" (??0UIHandling@@QAE@W4eType@@@Z) already defined in Bond.obj 
1>Company.obj : error LNK2005: "public: __thiscall UIHandling::UIHandling(void)" (??0UIHandling@@QAE@XZ) already defined in Bond.obj 
1>Date.obj : error LNK2005: "public: __thiscall UIHandling::UIHandling(enum eType)" (??0UIHandling@@QAE@W4eType@@@Z) already defined in Bond.obj 
1>Date.obj : error LNK2005: "public: __thiscall UIHandling::UIHandling(void)" (??0UIHandling@@QAE@XZ) already defined in Bond.obj 
1>GovStock.obj : error LNK2005: "public: __thiscall UIHandling::UIHandling(enum eType)" (??0UIHandling@@QAE@W4eType@@@Z) already defined in Bond.obj 
1>GovStock.obj : error LNK2005: "public: __thiscall UIHandling::UIHandling(void)" (??0UIHandling@@QAE@XZ) already defined in Bond.obj 
1>main.obj : error LNK2005: "public: __thiscall UIHandling::UIHandling(enum eType)" (??0UIHandling@@QAE@W4eType@@@Z) already defined in Bond.obj 
1>main.obj : error LNK2005: "public: __thiscall UIHandling::UIHandling(void)" (??0UIHandling@@QAE@XZ) already defined in Bond.obj 
1>Stock.obj : error LNK2005: "public: __thiscall UIHandling::UIHandling(enum eType)" (??0UIHandling@@QAE@W4eType@@@Z) already defined in Bond.obj 
1>Stock.obj : error LNK2005: "public: __thiscall UIHandling::UIHandling(void)" (??0UIHandling@@QAE@XZ) already defined in Bond.obj 
1>D:\Asaf\C\VS\hw5\HW5\Debug\HW5.exe : fatal error LNK1169: one or more multiply defined symbols found 

所以我去Bond.h和Bond.cpp，看看是否有什麼奇怪的東西（像的實現UIHandling::UIHandling()或類似的東西），並沒有。

我在另一個問題中看到，當你違反ODR這個錯誤，但我沒有。 In another similar question答案是，這與一遍又一遍地包含相同的文件導致構造函數的許多不同實現有關，但使用#ifndef _UIH命令可以避免這種情況。

它可能有一些做我如何聲明和定義構造函數我： 在UIHandling.h：

class UIHandling : public exception 
{ 
public: 
    UIHandling();   // Default C'tor - error unknown 
    UIHandling(eType);  // C'tor with error type 
    template <class T> 
    UIHandling(eType, T); // C'tor with error type and relevant number 
... 
} 
... 
UIHandling::UIHandling() 
{ 
... 
} 

UIHandling::UIHandling(eType e) 
{ 
... 
} 

template <class T> 
UIHandling::UIHandling(eType e, T number) 
{ 
... 
} 

任何幫助嗎？

Answer 1

如果您要在類之外和標題中定義成員函數，則需要使用關鍵字inline，並確保每個翻譯單元僅包含一次標題的內容（即每個cpp文件包含一次，這是通過標題完成的包括警衛或#pragma once）。

class UIHandling : public exception 
{ 
public: 
    UIHandling(); 
    // ... 
}; 

inline // << add this... 
UIHandling::UIHandling() 
{ 
} 

該cppreference爲inline;

An inline function is a function with the following properties:

1. There may be more than one definition of an inline function in the program as long as each definition appears in a different translation unit. For example, an inline function may be defined in a header file that is #include'd in multiple source files.
2. The definition of an inline function must be present in the translation unit where it is called (not necessarily before the point of call).