错误LNK2019:无法解析的外部符号，C ++ [英] ERROR LNK2019:unresolved external symbol, c++

问题描述

我已经为地图/字典数据结构编写了一个模板类，并不断收到这个奇怪的错误(ERROR LNK2019:未解析的外部符号)

I have written a template class, for a map/dictionary data structure, and keep getting this strange error (ERROR LNK2019:unresolved external symbol)

代码:

AssArray.h:

AssArray.h:

#pragma once   
template <class K,class D>   
class AssArray   
{   
    int _size;   
    int _position;   
    D* _data;   
    K* _key;  

public:    
     AssArray(int);
    ~AssArray(void);

    const D& operator [](K k) const;
    D& operator [](K k);
};

AssArray.cpp:

AssArray.cpp:

#include "StdAfx.h"
#include "AssArray.h"

template <class K,class D>
AssArray<K,D>::AssArray(int size)
{
    _size=size;
    _data = new D[size];
    _key = new K[size];
    _position=0;
}

template <class K,class D>
AssArray<K,D>::~AssArray(void)
{
        delete[] _data;
    delete[] _key;
}

template <class K,class D>
const D& AssArray<K,D>::operator [](K k) const
{
    //Get
    for(int i=0;i<_position;i++)
        if(_key[i]==d)
            return _data[i];
    return NULL;
}

template <class K,class D>
D& AssArray<K,D>::operator [](K k)
{
    //Set
    for(int i=0;i<_position;i++)
        if(_key[i]==d)
            return _data[i];

    if(_position<_size-1)
    {
        _key[position]=d;
        _position++;
        return _data[_position];
    }
    else
    {
        //Implement error handling
    }

}

错误为:
1

The errors are:
1

"Error  4   error LNK1120: 3 unresolved externals   
C:\Users\*****\Documents\Visual Studio 2010\Projects\OOPLAB4NYARE\Debug
\OOPLAB4NYARE.exe   1   1   OOPLAB4NYARE"

2

Error   1   error LNK2019: unresolved external symbol "public: __thiscall 
AssArray<char *,float>::~AssArray<char *,float>(void)" (??1?$AssArray@PADM@@QAE@XZ)
referenced in function _wmain   C:\Users\*****\Documents\Visual Studio
2010\Projects\OOPLAB4NYARE\OOPLAB4NYARE\OOPLAB4NYARE.obj    OOPLAB4NYARE

3

Error   3   error LNK2019: unresolved external symbol "public: __thiscall
AssArray<char *,float>::AssArray<char *,float>(int)" (??0?$AssArray@PADM@@QAE@H@Z) 
referenced in function _wmain   C:\Users\*****\Documents\Visual Studio 
2010\Projects\OOPLAB4NYARE\OOPLAB4NYARE\OOPLAB4NYARE.obj    OOPLAB4NYARE

4

Error   2   error LNK2019: unresolved external symbol "public: float & 
__thiscall AssArray<char *,float>::operator[](char *)" 
(??A?$AssArray@PADM@@QAEAAMPAD@Z) referenced in function _wmain C:\Users\Jonathan
\Documents\Visual Studio 2010\Projects\OOPLAB4NYARE\OOPLAB4NYARE\OOPLAB4NYARE.obj   
OOPLAB4NYARE

我正在使用Microsoft Visual Studio 2010 Ultimate.这很可能是我一直忽略的事情.

I am using Microsoft visual studio 2010 Ultimate. It's most likely something easy I've just been overlooking.

我试图清理->重建，创建一个新项目并复制粘贴相关代码，并试图找到一种解决方案，但是我所看到的却千差万别，而且模棱两可.

I have tried to clean->rebuild, created a new project and copy pasted the relevant code, as well as trying to find a solution, but the ones I've seen are pretty varied and vague.

推荐答案

您不能将类模板的成员函数定义放在.cpp文件中.

You cannot put member function definitions for a class template in .cpp files.

在处理包含该调用的翻译单元(即.cpp文件)时，编译器必须在调用 时看到类模板的成员函数的定义.这允许编译器实际生成代码.除非调用这些函数，否则不会实例化.

The definitions of member functions of a class template must be seen by the compiler at the point those functions are invoked, while processing the translation unit (i.e. .cpp file) that contains that invocation. This allows the compiler to actually generate the code. No instantiation occurs unless those functions are invoked.

现在，通过将函数定义放入不包含这些函数调用的.cpp文件中，基本上就是:

Now by putting your function definitions in a .cpp file which contains no invocation of those functions, you are basically:

1. 将它们密封到没有其他.cpp文件没有机会看到它们的地方；
2. 避免在唯一可以看到其定义的.cpp文件中对这些函数进行任何实例化.

1. sealing them into a place where no other .cpp file has a chance to see them;
2. avoiding any instantiation of those functions in the only .cpp file that can see their definitions.

因此，编译器不会为它们生成任何目标代码，链接器最终会抱怨找不到相应的符号(这是您得到的错误).

Therefore, the compiler will not generate any object code for them, and the linker will eventually complain that the corresponding symbols are not found (that's the error you get).

要解决此问题，请将类模板的成员函数定义移到类模板定义所在的同一标头中(在您的情况下为AssArray.h)，或者将其移到转换单元#include d的标头中(s)调用这些功能的位置(以及在调用点之前 处).

To solve the problem, move the member function definitions of your class template into the same header where the class template definition is (AssArray.h in your case), or in a header which is #included by the translation unit(s) where those functions are invoked (and before the points of invocation).

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