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Templates question

Started by Rattrap Apr 11, 2005 at 12:27 PM 2 replies 650+ views

Original Post

Rattrap

125

Rattrap

Apr 11, 2005 at 12:27 PM

There is probably just something really stupid wrong with this code.


//  Header File
template <typename T>
class CDoubleLinkList
{
public:
	CDoubleLinkList(void);
	~CDoubleLinkList(void);

protected:

private:

};


//  Cpp File
#include "CDoubleLinkList.h"

template <typename T>
CDoubleLinkList<T>::CDoubleLinkList(void)
{
}

template <typename T>
CDoubleLinkList<T>::~CDoubleLinkList(void)
{
}

Nothing real fancy yet. They don't even do anything yet. But I tried compiling this


#include "CDoubleLinkList.h"

int main(void)
{
	CDoubleLinkList<int> dllTest;
	return 0;
}

and get this back main.obj : error LNK2019: unresolved external symbol "public: __thiscall CDoubleLinkList::~CDoubleLinkList(void)" (??1?$CDoubleLinkList@H@@QAE@XZ) referenced in function _main main.obj : error LNK2019: unresolved external symbol "public: __thiscall CDoubleLinkList::CDoubleLinkList(void)" (??0?$CDoubleLinkList@H@@QAE@XZ) referenced in function _main I have tried looking at various how to template stuff, and I think what I wrote looks correct. I will note I'm using Visual Studio C++ 2005 Express Beta, so it is possibly something wrote with the compiler.

rick_appleton

213

rick_appleton

Apr 11, 2005 at 12:30 PM

When using templates, all the code has to be in the .h file. Move the code there, and all should be well.

Rattrap

Author

125

Rattrap

Apr 11, 2005 at 12:30 PM

Thanks. I figured it was something stupid.

snk_kid

131

snk_kid

Apr 11, 2005 at 12:59 PM

As partially noted already, it's not exactly true that template code needs to be all in header but they definitely need to be the same translation unit unless your compiler supports the export keyword which nearly none do. If you really wanna sperate your code you can always put definitions into another file (it can have any file extension) and include at the end of the header.

Also note the C++ standard library provides containers and algorithms including a list type known as std::list in header *list*, there-for you should use that if you just want to use a list.

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