本文介绍了C++ 模板友元函数未链接的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

我有以下在 VC6 中编译的代码:

I have the following code which compiles in VC6 :

文本.h:

template <typename T>
class CTextT
{
   public:

    friend  CTextT add(const CTextT& text1, const CTextT& text2) ;

friend CTextT operator+(const CTextT& string1, const CTextT& string2)
    {
       return ::add(string1, string2);}
    }

    ....................
};

在标题的末尾

 #include "Text.inl"

Text.inl:

template <typename T>
CTextT<T> add(const CTextT<T>& text1, const CTextT<T>& text2)
{
    CTextT<T> temp ;

    // do something

    return temp ;
}

但是 VC2010 给了我 LINK 错误:

But VC2010 gives me LINK error:

error LNK2019: unresolved external symbol "class CTextT<char> __cdecl add(class     CTextT<char> const &,class CTextT<char> const &)" (?add@@YA?AV?$CTextT@D@@ABV1@0@Z)
referenced in function "class CTextT<char> __cdecl operator+(class CTextT<char> const &,class CTextT<char> const &)" (??H@YA?AV?$CTextT@D@@ABV0@0@Z)

 1>.DebugUnitTestText.exe : fatal error LNK1120: 1 unresolved externals

如果我将代码放在 Text.h 中,它可以很好地编译.但我不想这样做,因为我想从实现中保持声明干净.当函数在类之外时,我不明白为什么链接器在这种情况下会抱怨?这是唯一的问题,类非常大,还有其他返回 CTextT 的友元函数.

If I place the code in the Text.h it compiles fine. But I do not want to do this because I want to keep declaration clean from implementation. I can't figure why linker is complaining in this case when the function is outside the class? This is the only problem and the class is very big and there are other friend functions returning CTextT.

推荐答案

解决方案如下:

template <typename T>
class CTextT
{
public:

template <typename T>
friend CTextT<T> add(CTextT<T> const&, CTextT<T> const&) ;

friend  CTextT<T> operator+(const CTextT<T>& string1, const CTextT<T>& string2)
{  return ::add(string1, string2); }

};

template <typename T>
CTextT<T> add(CTextT<T> const&, CTextT<T> const&)
{
   CTextT<T> temp ;
   return temp ;
}

我发现以下 MSDN 链接解释了如何在模板中添加友元函数 - http://msdn.microsoft.com/en-us/library/f1b2td24.aspx.

I found the following link to MSDN explaining how to add friend functions in templates - http://msdn.microsoft.com/en-us/library/f1b2td24.aspx.

我测试过,它适用于 VS2010 和 VS2012.VC6 不需要第二个模板声明(它从类中获取)并且在 VC6 中此代码将不再编译 - 将返回内部编译器错误.

I tested and it works for VS2010 and VS2012. VC6 does not need the second template declaration (it takes it from the class) and in VC6 this code will not compile anymore - will return INTERNAL COMPILER ERROR.

这篇关于C++ 模板友元函数未链接的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!

05-27 15:48
查看更多